# 1975 MG Midget 1500 engine CAD study

Selecting a filter part in the browser now opens a six-step PF53 study. It
separates the canister and gasket from the modeled head and adapter so their
connection order can be inspected. The fitted PF53 number comes from owner
photo IMG_6966; the canister envelope and gasket diameters come from a PF53
catalog listing. The modeled adapter thread, seal seat, installed clearances
and illustrated movement are unverified. The animation is a visual study,
not a filter-removal path or proof that a replacement will fit. The inspector
now records direct canister diameter and height, an obstacle distance from the
filter mounting plane, the inspected adapter-thread choice, and removed-gasket
inside and outside diameters. Direct canister and gasket dimensions can reshape
only those solids in a separate owner STEP; access distance and thread choice
stay in its provenance and do not alter the provisional head or adapter. A
recorded obstacle gap is only the straight space below the installed canister,
not verified rotation or an exit path. A browser preview stretches the catalog
canister mesh and maps the gasket's two radii to recorded values, then can be
switched back to the catalog study. The downloadable public STEP is unchanged;
the separate owner build reconstructs the measured canister and gasket solids.

The upper adjusting-link worksheet now records the tab-hole center's sideways
and vertical offsets from the alternator upper-ear bolt. In a front view,
positive sideways points toward the alternator and positive vertical points
upward. Capture both centers with a ruler in the same plane, or measure the
components directly on the installed assembly. These values stay in the
exported measurement log and accompany any owner build that also has a
supported direct dimension; they cannot safely reshape the present
hand-sketched link until its fitted anchor, profile and bend are documented.

The crank pulley now has two distinct grooved cores. Previously, its large
rear core filled the smaller forward groove in the actual solid. The crank,
pump and alternator pulley grooves now use 36° walls and an 11 mm depth
from the [SAE J636 10A comparison table](https://www.normsplash.com/Samples/SAE/152125733/SAE-J-636-2019-en.pdf#page=4).
Its 9.7 mm effective width is used as a provisional visual mouth opening;
those are different measurement datums.
The Midget parts listing establishes a nominal 3/8-inch belt class; it does
not prove that this 2019 standard profile or any modeled groove is fitted to
the car. `verify_drive_lane.py` checks that both crank grooves are actually
open in the solids and that the shared virtual belt lane remains aligned.

The belt's three contact circles now sit seven millimeters inside each
modeled pulley rim. Its formerly rectangular solid floated outside the pump
and alternator grooves and intersected the crank pulley. A tapered V section
now clears all three virtual pulleys by about 0.1 mm; the verifier measures
those gaps and checks for solid intersections. This is an internal fit check,
not a belt-size recommendation. The resulting approximate outer loop is
about 990 mm, whereas a CHA328/GFB11113 comparison belt is listed near
1113 mm. The unknown pulley centers, fitted belt variant and length datum
must be established on the car before selecting a replacement.
The browser's local pulley-diameter preview uses the same three contact
setbacks and a tapered belt mesh; it changes no downloadable STEP until a
separate owner build is made.
The worksheet's three-center outline calculation now also uses that same
setback on the crank, pump and alternator. With every other provisional
dimension frozen, reaching an 1113 mm model outside loop solely by rotating
the 91 mm virtual alternator pivot-to-shaft radius requires an approximately
58.6° outward swing from its upright model position. This is a sensitivity
calculation, not an available adjustment range or a fitted belt-length datum.
The belt inspector now draws the provisional pulley centers and belt outline
over a separate triangle reconstructed from three directly recorded shaft-center
distances. Both share the same provisional groove profile. The recorded
triangle is rotated to place the crank-to-pump line upright; these distances
alone cannot locate the pump horizontally on the engine or set an installed
alternator angle. Outside rings and center distances remain visible so the
viewer can see which part of the discrepancy comes from layout.

A separate owner front-drive STEP can now be generated from that same exported
three-center log. Run `/tmp/midget-cad-venv/bin/python build_front_drive.py
--measurements /path/to/midget-1500-cad-measurements.json --output-dir
/tmp/midget-owner-drive` from this directory. The output contains only the
three pulleys and a comparison belt; it does not move the public engine,
water-pump housing, alternator bracket or fan. The generator rejects impossible
triangles and overlapping pulley envelopes. It uses direct pulley outside
diameters from the log when present, otherwise the public comparison values.
The three lengths leave rotation and reflection ambiguous, so this separate
study explicitly puts the pump on the crank's vertical model axis and the
alternator on the positive-X side. Its JSON records every center, applied
diameter, source note and remaining assumption. A square-on car view or direct
X/Y center offsets are still needed before the pulley stations can become
fitment geometry in the full engine assembly.

The [front-drive photo survey](../front-drive-survey/) can mark one known ruler
length and all three shaft centers on the same square-on image. It downloads a
JSON log with `method: photo`, the image filename, scale, marks and three
estimated distances. The image remains in the browser. The isolated STEP
builder rejects this log by default; add `--allow-photo-estimate` to the command
above to generate a clearly labeled **photo estimate** for visual planning.
Perspective, a ruler at another depth and center-identification errors remain
unquantified, so such a build cannot establish belt size or clearance.
The survey's **Compare in engine CAD** button keeps the result in local browser
storage and opens the belt inspector, where a blue photo triangle appears
beside the dashed public model and any orange direct-measurement triangle.
The CAD inspector can also import the downloaded survey JSON and remove the
photo estimate. This separate overlay never overwrites direct measurements or
changes the public 3D engine.

The [factory workshop manual, part 3, PDF p. 9](https://www.spridgets.de/downloads/Midget%201500%20WH%20Teil%203.pdf#page=9) gives distinct front-mount removal operations 12.45.01 (left) and 12.45.03 (right). The scanned page is headed **U.K. specification**. Its order of access, fastener separation and engine support is documented in the [mount guide](../engine-mounts/#factory-removal) as a comparison; North American applicability, support points, tightening values and actual clearances still need verification. These instructions do not establish bracket or rubber geometry in the STEP.

The browser's View controls now include a Cutaway view. Choose a side and move the slider to hide near-side mesh surfaces, making internal parts easier to inspect and select in place. The cut has no solid caps; it is a viewing aid, not evidence of wall thickness, machining, or service clearance. Reset view restores the full assembly.

The inspector offers both an assembly view and a part-only view. The latter hides attached context and permits closer zoom for a small casting, bolt or seal, without the pulley, fan or neighboring pieces in front of it; it does not prove the hidden pieces can be removed in that order. When focused, the Front, Rear, Top, Bottom and side camera buttons rotate around the selected view and retain its zoom. The exploded-view slider and a phone-width or orientation change recalculate the focused framing so separated parts stay visible. Reset view returns to the whole engine.

IMG_6971–6972 show one exposed metal member crossing the dark band between the alternator's silver case halves. The STEP now includes its visible span as a separate selectable comparison piece. Its complete fastener form, diameter, radial clocking and hidden counterparts are not established by those photographs.

IMG_6976 also shows fine circumferential lines on that band. Fifteen shallow grooves in the CAD convey the visible surface pattern. Their count, pitch, depth and physical interpretation are unmeasured; the grooves are not clearance or machining data.

## End target

The starter is now a nineteen-part selectable M35J study: hollow yoke, four pole shoes, four pole-shoe screw cues, armature, face commutator, insulated brushbox, four wedge brushes, two-hole drive end, two mounting bolts, photo-led smooth commutator-end bracket, terminal, separate shaft, screwed sleeve, thrust collar, main spring, shroud washer, circlip and pinion. The [factory Midget 1500 parts list](https://www.spridgets.de/downloads/Parts-1977.pdf#page=185) specifies Lucas M35J assembly 13H5798, pinion/barrel 67H5010 and two BH606071 mounting bolts. A [Lucas starter drawing](https://forum.lrsoc.com/forum_files/Lucas%20Starters.pdf#page=12) supports the 88.9 mm yoke outside diameter. The [Lucas M35J workshop sheet](https://www.motorarkiv.dk/books/dvk007558.pdf#page=87) establishes the windowless hollow yoke, four pole shoes, armature, face commutator and drive items 17–21 (screwed sleeve, thrust collar, main spring, shroud washer and circlip); their CAD sections, stations, clearances and travel remain estimates. The [July 1975 M35J bench page, PDF p. 89](https://www.motorarkiv.dk/books/dvk007558.pdf#page=89) identifies the four wedge-shaped brushes and brushbox, the spring-compression tool needed to expose an SB-drive circlip, an approximately 8 mm brush renewal point and approximately 7.80 N brush spring pressure. The CAD brushbox outline, brush shape, contact gap and wiring remain estimates or omissions. Lucas Fig. 1 lists four pole-shoe retaining screws; the separate shallow screw-head cues use that count, while their size and stations remain unmeasured. The [current Midget starter listing](https://rimmerbros.com/ItemList--MG-Midget-1500-Starter-Motors--m-24546) labels 67H5010 as nine-tooth. The inertia-drive spring is now a swept helix rather than a stack of flat rings; its pitch, wire gauge, diameter, handedness and end geometry are still study estimates. The flange’s 125.45 mm hole spacing follows an [HC-Cargo 111103 compatible replacement listing](https://wagendass.com/en/starter-for-ford-mercury-triumph/8913-starter-replacing-LUCAS-25239-25201-25149-25138-25097-5902129028611.html), not a measurement of this car. The yoke is now about 150 mm long and the longer drive follows the replacement’s published front/rear envelope only as a proportional guide. Remaining dimensions and the installed station are provisional; the pinion is parked clear of the modeled flywheel. IMG_6966 and IMG_6969–6970 show its casing and dark, mostly smooth terminal end on the distributor/oil-filter side, but no readable marking identifies the fitted model or establishes exact mount coordinates. The [starter field guide](../starter/) records what to measure before using the CAD for a replacement plan.

Selecting any starter part now opens a seven-step Lucas M35J bench study in the CAD. It identifies the fitted-unit gate, connection and mount observations, SB-drive circlip and shroud relationship, the separate drive stack, end-bracket boundary and four-brush inspection. Only the bench anatomy is animated; the spring-compression tool, vehicle removal path, installed clearances and real reassembly are not simulated. The source is the July 1975 M35J workshop instruction sheet, especially PDF pages 87 and 89.

The starter inspector can record the fitted type, direct yoke outside diameter, direct axial body length and direct mounting-hole center spacing. A separate owner build applies those three dimensions only when the entry confirms an M35J: the hollow shell and rear cap change, internal study sections move axially, and both flange ears and bolt cues move symmetrically along a provisional axis. The flange clocking, installed center coordinates, profile and pinion position remain unmeasured. The project planner has a starter inspection template. The accessible parts plate does not provide a verified removal sequence or tightening values, so neither the guide nor CAD presents those as established.

Build a 1:1 virtual version of **this car** that the owner can use to rehearse a replacement before touching the real assembly. That requires measured mounting coordinates, access clearances, fitted part numbers and variants, and a repair sequence checked against the factory procedure and the photographed car. A component is ready for a virtual replacement guide only when its geometry and removal path have been checked against direct car measurements and its fasteners, tools, safety conditions and reassembly checks are documented. The current model is progress toward that target, not yet a validated virtual twin.

The block now has three separately selectable 144688 side core plugs. The [Midget 1500 parts listing](https://rimmerbros.com/images/PDFs/SMCAT.pdf) calls for three, and [Rimmer specifies a nominal 1½-inch diameter](https://rimmerbros.com/Item--i-144688). A [related Spitfire MkIV block photograph](https://spitfiremk4.wordpress.com/2016/02/05/le-bloc-moteur/) places a three-plug row and raised seats on the ignition side. The model includes raised cast seats with estimated 47 mm outside diameter and 4 mm projection; only the plug diameter is catalog-sized. The inspector accepts a direct outside diameter and projection for each seat; those measurements change only that seat in a separate owner STEP. Their actual centers, cup depth, fit and nearby access on this car remain unmeasured. The separate [core-plug field guide](../core-plugs/) records what must be checked before planning a replacement. The Moss external-engine plate shows a large and a small front-face plug in addition to the three side plugs. Both are now separately selectable behind the provisional front engine plate. The factory listing gives 144688 quantity four at nominal 38.1 mm and 144687 quantity one at nominal 25.4 mm; the mapping to Moss numbers 328-205 and 319-015 is inferred from the plate. Front centers, cup depth, wall and access remain unmeasured. Other block plugs remain outside this seven-part study.

The head now has two separate rear-face core-plug cups and open sockets. The [Midget 1500 head plate](https://mossmotors.com/media/wysiwyg/catalogpdf/spm_catalog_web.pdf#page=34) shows one large and one small head cup; the [1500-family parts catalogue](https://lococlassics.nl/wp-content/uploads/2018/11/Spitfire-MKIV-1500-Parts-1.pdf#page=56) names AEH592 at nominal 1⅝ inches (41.275 mm) and 144686 at 1¼ inches (31.75 mm). A [Moss listing for a large replacement cup](https://mossmotors.com/328-235-core-plug-cupped-1-41-64) gives 1 41/64 inches instead; the catalogue values are comparison envelopes, not a bore or press-fit specification. Their rear-face XY centers, 4 mm virtual cup depth, socket clearance and actual fitted-head variant are unmeasured. Boolean checks find zero overlap between each virtual cup and the head. The [field guide](../core-plugs/#head-plugs) asks for the observations needed before any head-plug repair plan.

The four spark plugs are now separately selectable by cylinder, numbered from the fan end. The [Moss Midget 1500 specifications](https://mossmotors.com/1500-midget-gan6) list Champion N12Y and a .025-inch gap; [Champion’s shell-code reference](https://www.championautoparts.com/Technical/Tech-Tips/decoding-champion-spark-plugs.html) gives the N shell a nominal M14 × 1.25 thread, .750-inch (19.05 mm) reach, gasket seat and 13/16-inch (20.64 mm) hex. The former virtual plug had a 12 mm thread-length silhouette and a 19 mm polygon diameter, so its socket relationship was misleading. The new model uses those published N-shell dimensions and has four individual side-entry head bores. This is a period reference, **not proof that N12Y plugs remain fitted**. The head station, angle, real thread fit, hex height, ceramic, gasket, electrode shape and boot clearance are not measured. A visible ground strap and center electrode show the period 0.635 mm gap only as a functional study; they cannot diagnose wear or set the fitted plug. The model represents the nominal thread envelope without helical threads. Read the installed plug marking and measure access before choosing parts or tools.

The viscous-fan assembly now exposes the [UKC759 tolerance ring](https://rimmerbros.com/Item--i-UKC759) as a separate selectable sleeve between the pump drive and [UKC3532 coupling](https://rimmerbros.com/Item--i-UKC3532). The supplier photos establish a split, axially corrugated ring and a coupling with dense radial fin fields. The STEP and browser shapes show those recognition features and the coupling socket. A direct diameter across the finned disc and direct axial length of a loose replacement ring can resize those two specific features in a separate owner STEP. The ring bore, corrugation count, fit, axial seat, coupling depth and fins remain unmeasured estimates; do not use this virtual fit as a puller, interference or clearance specification. [British Parts Northwest](https://bpnorthwest.com/water-pump/fan-clutch-slip-ring/) describes UKC759 as a one-use crush ring, and the [Moss Midget catalog](https://mossmotors.com/media/wysiwyg/catalogpdf/spm_catalog_web.pdf#page=37) says to renew it each time the fan clutch is removed and replaced.

The radiator cowl is now a separate selectable STEP/browser part. [Moss 459-775](https://mossmotors.com/459-775-cowl-radiator) and [Rimmer CHA281](https://rimmerbros.com/ItemList--MG-Midget-1500-Radiator-Cowls-Fan-Guards--m-24688) identify the open folded frame, and IMG_6854 shows the black upper bridge on the car. The CAD now includes the open bridge, two standing flanges with four supplier-photo hole cues, a sloping apron and two side returns above the existing aftermarket-core envelope. Their width, front-to-back extent, sheet gauge, bend profiles, hole positions and body station are estimates; it does not assert a fitted fan-to-cowl clearance or a drill pattern. The viewer moves the cowl with the radiator comparison when a directly recorded fan-to-core gap shifts that body-mounted assembly.

IMG_6849/6854 now anchor a separately selectable, body-fixed expansion-tank shell and cap in the STEP and browser. The shell uses a tapered loft with a raised perimeter seam, filler neck and hose-neck recognition shape, not the former generic rectangular envelope. Its public 94 × 145 × 66 mm outside size and station are photo-layout estimates, and the cap contains no seal geometry. The [factory standard cooling plate, PDF p. 86](https://www.spridgets.de/downloads/Parts-1977.pdf#page=86) identifies ARA 326/GRC 110; the [75-A-6 modification plate, PDF p. 87](https://www.spridgets.de/downloads/Parts-1977.pdf#page=87) identifies URP 1148/URP 1145. [MGOC describes the standard 1500 tank as plastic](https://www.mgocspares.co.uk/parts/mg/midget/cooling/radiators-coolant-hoses), and a [photographed used ARA 326](https://www.robertpieces.com/en/used-parts-for-british-cars/4675/expansion-tank-mg-midget-1500-1974-80-detail) shows a molded number on the broad rib below its filler neck and two mounting ears. Those features make ARA 326 a useful comparison, not an identification of this car. Neither the photographed shell nor its cap has a verified part number yet, and the bulletin says its double-seal cap is not interchangeable with the original. The inspector records the observed marking, direct shell width/height/depth, and three positional offsets from the finned radiator core: horizontal distance from its intake-side edge to the tank's inboard shell face, vertical drop from core top to shell top, and rearward distance from the core's rear face to the shell's rear face. The public offsets (49, 64.5 and 59 mm) are estimates. Exported direct values resize and move the tank in a separate owner STEP. A browser preview that repositions the radiator from direct core measurements moves the tank with it, preserving the *estimated* relative offsets; directly recorded tank offsets are applied only in the owner STEP. The mounting bracket, shell wall, neck positions, seal and hose route stay provisional. The [cooling identification guide](../cooling-history/) shows the checks needed before choosing a cap or tank.

The red rocker cover now has open passages for its two hold-down studs and a hollow oil-filler neck; the cap is a separate removable part. This corrects solid material that previously occupied those interfaces. The [MGOC 1500 upper-engine catalog](https://www.mgocspares.co.uk/parts/mg/midget/engine/upper-engine-components/1500cc) documents the early two-stud arrangement, while the photographed cover sets the visual placement. Passage diameters (9 mm at the studs, 30 mm at the filler), neck height, locking detail and seat shape are **provisional reconstruction geometry**, not parts specifications. The cover inspector can now export a directly measured 20–50 mm clear filler-opening diameter for a separate owner STEP build. Measuring the opening does not establish which cap locks and seals on it.

The photographed Zenith-Stromberg cover has named owner-measurement fields for its widest round dome diameter, square-edged flange width and length, and the yellow damper cap's maximum lobe-to-lobe diameter. The public study begins at **68 mm dome, 73 × 71 mm flange and 35.4 mm cap**; these are visual reconstruction sizes, not measurements of the fitted car. Exporting direct measurements from those two selected CAD parts and running the separate owner build replaces only those outside dimensions. The mating seat, diaphragm ring and two approximate screw markers follow the changed cover envelope, but that does **not** verify their real sizes or screw centers. IMG_6958 also shows an offset raised casting beside the neck; it is modeled as part of the cover. The body now includes unmeasured passage lips, a lower ledge and side bosses based on the factory CD4 assembly silhouette. None of these new surfaces is a measured mounting, port or adjustment datum. Cover height, inner clearance, screw count and threads, cap seal, fitted carburetor tag and the actual removal path remain unknown. A photo estimate is retained in the inspector but cannot drive the owner STEP.

IMG_6854–6855 show a hose clamped to the intake side of this red cover. The [factory 1975–77 emissions breather plate, PDF p. 68](https://www.spridgets.de/downloads/Parts-1977.pdf#page=68) identifies a rocker-cover-to-T-piece hose (154220), T-piece (154211), and onward hoses to the carburetter and carbon canister. [MGOC's 154220 replacement listing](https://www.mgocspares.co.uk/product/154220/hose-breather-rocker-cover-to-tee-piece) gives a 7/16-inch (11.1125 mm) inside diameter and 3¼-inch (82.55 mm) length; the STEP hose bore now uses that catalog value. The STEP also has a hollow side outlet and separately selectable short hose end and clamp. The six-stage cover study disconnects that hose before raising the cover. The outlet position, its 11 mm modeled outside diameter, the 42 mm displayed straight hose segment, hose outside diameter, clamp dimensions and downstream route are **photo-informed placeholders**; the short segment is not the catalog hose length. Trace and measure the fitted hose before using this model for replacement planning.

IMG_6854–6855 also show four orange ignition leads looping outboard of the cover. The STEP and browser now include four separately selectable curved leads and black plug-end sleeves, so the displayed cover-access area no longer omits them. Their 7 mm modeled outside diameter, exact paths, lengths, clips, terminal boots and cap-post assignments are **provisional**. A [reproduced 1975 Midget 1500 handbook specifications page](https://fliphtml5.com/fmlf/hepw/MG_Midget_1975/45/) lists the firing order as 1-3-4-2, but the photographs do not establish which post on this car's distributor cap serves each lead. The virtual post assignments are only layout geometry. Photograph and label both ends of each fitted lead before disconnecting one; do not use the virtual wiring as a reconnection guide.

IMG_6853 and IMG_6859 show the large thermostat-housing outlet on the ignition side, with a smaller hose on the other side. The earlier CAD had one solid outlet facing the wrong way. The housing now has two hollow side necks, and a separately selectable hollow upper radiator hose and clamp follow the broad bend visible across the alternator in IMG_6853. The clamp includes a worm-drive screw housing and slotted head for recognition. Its 44 mm modeled outside diameter, 36.6 mm bore, bend, clamp, housing port dimensions and station are **not measured**. The modeled hose stops short of the provisional radiator core; the installed radiator neck and final connection are not established. The [August 1975 British Leyland overheating bulletin](https://chicagolandmgclub.com/techtips/tsb/TSB_no75a6.pdf#page=3) illustrates a modified thermostat housing and upper-hose tee, while the [Moss 1500 cooling plate](https://mossmotors.com/media/wysiwyg/catalogpdf/spm_catalog_web.pdf#page=37) distinguishes 1975 cooling parts. Neither proves which modification, if any, is fitted to this car. Trace and photograph the complete cold hose assembly before ordering or removing parts.

IMG_6895 and IMG_6896 show the lower radiator hose clamped to the housing and turning down in a broad bend beside the fan. The CAD now gives this visible section and its housing-end worm-drive clamp separate selectable parts. The hollow hose uses a **43 mm outside / 35 mm inside comparison envelope**, follows the provisional casting neck when its exposed length changes, and stops before the hidden radiator connection. These diameters, 3D route, clamp size and orientation are photo estimates, not measurements of the fitted hose. The model cannot select a replacement, establish its unseen radiator joint, or prove fan, belt or removal clearance. Photograph both ends and measure both metal necks and the closest clearances directly before a hose project.

The lower-hose inspector now accepts a direct outside diameter on a straight installed section (28–75 mm) and a direct relaxed bore if the hose is removed (20–60 mm). Either can resize the sleeve in a separate owner STEP; the clamp band follows its outside diameter. Without a direct bore, the build uses a **comparison** bore 1 mm larger than the recorded or provisional housing neck and retains an 8 mm total wall envelope unless a direct outside diameter replaces it. The builder rejects a sleeve wall under 2 mm and a gross bore/neck mismatch rather than presenting an impossible connection as a fit. Effective dimensions and whether each is direct or derived appear in the web geometry checks. Those derived values do not identify a replacement hose or validate a seal, clamp or route.

[Gates lists its flexible 25255 hose](https://www.gates.com/us/en/fluid-power/engine-hose/coolant-hose.p.4254-000000-000000.v.4254-00076.html) at 32 mm inside diameter; [its catalog](https://www.gates.com/content/dam/gates/home/knowledge-center/resource-library/catalogs/gates-industrial-engine-catalog.pdf) lists approximately 40.5 mm outside diameter. That is useful comparison data, but 25255 has not been identified on this car and its universal form does not establish the fitted molded-hose dimensions. The model's present 36.6/44 mm bore/outside pair remains provisional pending a direct cold-car measurement.

The cover's two fixed studs are now separate from the removable nut and washer stacks in both STEP and the browser study. The [Moss Midget 1500 cylinder-head plate](https://mossmotors.com/media/wysiwyg/catalogpdf/spm_catalog_web.pdf#page=33) lists two 4⅛-inch studs, two nuts, two plain washers and two fiber washers through 1976. The CAD shows only provisional exposed stud portions; its hidden threaded anchors, installed projection, washer sizes and thread details are unknown. During the virtual gasket study, the nuts and washers lift while the studs remain at the head, and the cover lifts over them. This corrects the earlier animation that raised all hardware together.

The [factory Sprite/Midget parts catalogue, PDF p. 63](https://www.spridgets.de/downloads/Parts-1977.pdf#page=63) supplies the original exploded cover drawing and lists separate early fiber washers, plain washers and nuts alongside the later North American O-ring hardware. The CAD inspector now links directly to that drawing for the cover assembly. It is a part-identification source, not a dimensioned casting drawing. Browser materials now distinguish the owner's red painted cover and pale fan from rough castings, rubber, fiber and bare metal; this changes appearance only. The starting camera moves closer on mobile and desktop. The browser tessellates prominent service parts at 0.7 mm / 0.16 radians instead of 1.4 mm / 0.28 radians, raising the mesh to about 310,000 triangles and 10.7 MB of JSON. This smooths curved displays; it does not improve the underlying STEP geometry or establish any new dimensions.

This is a **partial reconstruction**, in millimeters. `midget-1500-measured-core.step` is a STEP assembly made from `build_engine.py`. The browser view uses `midget-1500-measured-core.json`, tessellated from the same CadQuery shapes. Rebuild both with:

The oil sump is now modeled as an open pan rather than a solid block, with a separate selectable drain plug. The [1977 factory Midget parts plate B86, PDF p. 61](https://www.spridgets.de/downloads/Parts-1977.pdf#page=61) lists sump **213863** and drain plug **114774** and shows the plug low on the pan side. It does not dimension the pan, plug, installed side or drain station. Two supplier listings describe 114774 as a tapered, square-headed plug, but one calls its diameter 5/8 inch and the other 11/16 inch. The CAD now shows a smooth tapered shank about 15.5–16.5 mm across and a matching larger opening; neither is a verified thread, tool size or pan drilling. The pan wall, boss and plug station remain a topology and recognition study. See the [ANG listing](https://angclassiccarparts.co.uk/products/mg-5580/mg-midget-austin-healey-sprite/engine-parts-ancilliaries/gearbox-or-engine-sump-filler-plug-midget-1500) and [Rimmer listing](https://rimmerbros.com/Item--i-114774) for the differing descriptions. Verify the actual plug and pan from beneath the securely supported car before using this model to choose a tool or part. This change also makes the internal oil pickup visible when the sump is hidden or exploded; its clearance above the real sump floor remains unknown.

The same factory plate lists one **GEG517 gasket**, twelve **MA805** and four **HU805** sump screws. They now form separately selectable CAD groups, and an illustrative gasket occupies the interface between the block and the pan. The [MGOC Midget catalog](https://www.mgocspares.co.uk/DocumentHandler/136685/mgoc-spares-midget-catalogue-pdf) describes twelve short screws and four longer rear screws, with newer stock numbers and a different lock-washer count from the 1977 plate. Four CAD screws are grouped at provisional rear stations solely to show that comparison. The pan and gasket holes, screw stations, lengths, heads, gasket thickness and actual installed variants need direct checking. See the [sump project study](../sump/) for a field record, not a removal procedure.

The pan and plug inspectors now accept **direct owner measurements** from the fitted car: vertical block/pan-joint-to-lowest-outside-floor depth (85–140 mm), vertical joint-to-drain-center drop (25–115 mm), and distance forward from the rear pan-flange edge to the drain center (20–300 mm). An observed distributor/alternator or carburetor side can mirror the plug and boss. Export the measurement log and build a separate owner STEP/JSON. The builder moves the lower basin with the floor value and the plug and boss with the drain values; it rejects combinations leaving the provisional boss less than 17 mm above the floor. The public 106.5 mm floor depth, 68.5 mm drain drop and 70.2 mm rear-flange offset are reconstruction choices, not measured or factory dimensions. The flange size and engine station remain provisional, so even a directly measured plug offset does not validate its absolute engine position. The pan side profile, gasket, screw stations, plug head/thread/seal and pickup clearance on the real car still need evidence.

```sh
python3.11 -m venv /tmp/midget-cad-venv
/tmp/midget-cad-venv/bin/pip install cadquery==2.8.0
/tmp/midget-cad-venv/bin/python build_engine.py
/tmp/midget-cad-venv/bin/python verify_fit.py
/tmp/midget-cad-venv/bin/python verify_drive_lane.py
/tmp/midget-cad-venv/bin/python audit_pivot_path.py
```

`verify_fit.py` checks selected pairs that should not occupy the same volume in this study. It reports the adjusting-link/timing-cover overlap separately because the link's fitted mounting plane is still unknown. A zero-volume report checks the consistency of these virtual solids only; it does not certify actual installed clearances.

After an owner build, run `python verify_fit.py --measurements /path/to/midget-1500-cad-measurements.json` to repeat those checks with the same accepted dimensions. This is especially relevant when three direct bore-center intervals change the block and crankpin stations or four direct fan-hole centers move the fixing pattern.

`verify_drive_lane.py` probes the generated pulley solids and belt at the shared provisional plane. It guards against a future edit placing one visible groove away from the virtual belt; passing does not establish alignment on the fitted car.

The latest assembly adds a separately selectable oil pump body, cover, inner rotor/shaft, outer rotor, three mounting bolts, pickup tube and strainer. The [factory oil pump workshop page, part 3 PDF p. 10](https://www.spridgets.de/downloads/Midget%201500%20WH%20Teil%203.pdf#page=10) establishes the pump's three-bolt mounting, separate strainer and rotor inspection limits, but that page is labeled **U.K. specification**. The [Midget 1500 replacement listing](https://mossmotors.com/836-125-oil-pump-vertical-pick-up) and [replacement-pump photograph](https://motaclan.com/final_images/GLP145.jpg) inform the visible body and pickup form. Neither confirms the variant installed on this North American car. The [Midget 1500 lower-engine listing](https://www.mgocspares.co.uk/parts/mg/midget/engine/lower/1500cc) gives BH604221 pump bolts as 1/4 UNF × 2 3/4 in and GHF331 spring washers; the bolt shanks now use 6.35 × 69.85 mm nominal dimensions. Pump station, rotor profile, shaft engagement, mounting centers, pickup bend and sump-floor clearance remain guesses; the shaft is deliberately not connected to the provisional distributor drive. See the [oil-pump study](../oil-pump/) for an inspection plan.

The rear-drive study adds the flywheel, 117-tooth ring gear, four crank bolts, a matching-family 25.4 × 12.7 × 19.05 mm comparison pilot bush, 184.15 mm comparison clutch disc with twenty visual hub slots, clutch cover, six cover screws, three locating dowels and release bearing. The [Midget 1500 engine parts plate](https://mossmotors.com/media/wysiwyg/catalogpdf/spm_catalog_web.pdf#page=33) and [clutch plate](https://mossmotors.com/media/wysiwyg/catalogpdf/spm_catalog_web.pdf#page=52) establish the component counts; a [1975–79 replacement-disc listing](https://bpnorthwest.com/mg/clutch-disc-spitfire-75-to-80-mg-midget-75-to-79/) gives 7¼ in and 20 splines. A [ring-gear listing](https://philipsclassics.be/products/flywheel-ring-gear) gives 117 teeth, and a [matching Spitfire spigot-bush listing](https://www.scparts.co.uk/nl/spigot-bush/201050/) gives 1 in length, 1/2 in inside diameter and 3/4 in outside diameter. [Rimmer lists four 7/16-inch UKC4254 bolts for the Midget 1500](https://rimmerbros.com/Item--i-UKC4254), so the four CAD shanks and holes now use that nominal diameter. Their heads sit in the virtual flywheel recess instead of intersecting the clutch disc. The modeled 11 mm shank only reaches the reconstruction's thin crank flange; it is not a replacement length. [Rimmer also describes early USA Spitfire 1500s with 3/8-inch fixings](https://rimmerbros.com/Item--i-GRID005537), so the hardware on this Midget still needs inspection. The installed disc and gearbox, flywheel bolt variant and length, stock flywheel dimensions, bolt circles, actual tooth geometry and axial positions remain unverified. The [clutch study](../clutch-study/) explains the repair-planning limits and records to collect during access.

The factory dimensions in `../cad-data.json` govern bore, stroke, rod centers, main journal diameter, crankpin diameter, piston pin diameter, and valve head diameters. Their primary source is the MG Midget 1500 workshop manual, part 1, PDF pages 11–12: <https://www.spridgets.de/downloads/Midget%201500%20WH%20Teil%201.pdf>.

The crankshaft was rebuilt from the [factory workshop crank drawing, part 3 PDF p. 4](https://www.spridgets.de/downloads/Midget%201500%20WH%20Teil%203.pdf#page=4). It now exports as one connected solid with three main journals, four offset pins and joined cheeks; the previous straight shaft passed through the throws and its box-shaped webs floated apart. The modeled cheek width and rod-bolt stations were adjusted to clear the main caps and comparison rod housings, and the generated shapes are checked for those intersections. Factory stroke and journal diameters set the measured scale. Cheek outline, counterweights, journal widths and axial stations still need original drawings or direct inspection before the crank can support a bearing or machining decision.

The lower block has also been corrected around that crank. The previous shortened crankcase cavity buried the front and rear journals and lower caps in the block, while leaving the center cap without a mating upper saddle. The reconstruction now has three upper saddles, a longitudinal journal opening and lower end-wall openings. Boolean checks show zero volume intersection between the exported block and the crank, main caps, rods and rod caps. This establishes a coherent modeled assembly, not factory-accurate saddle contours or bearing clearances; direct dimensions and the proper bearing-shell geometry are still needed for a rebuild.

The public model's four bore centers use **79.5 / 86.5 / 79.5 mm photo-derived intervals**, a provisional layout estimate from the Ajusa gasket comparison below. No factory bore-center coordinate drawing has been verified here. The block inspector records the three adjacent distances independently. A separate owner build accepts all three direct measurements, shifting bore openings, pistons, rods, crankpins, valve stations and gasket openings; the outer castings and main-bearing stations remain provisional. The current builder supports individual intervals of 77–100 mm with at most 260 mm between the first and fourth bore centers; larger values need the crank and block envelopes revised. Measure all three intervals during a planned head-off repair before using the model for a head, gasket or block decision.

The same Ajusa photo supplies a more faithful gasket-hole pattern. A regular row of five near each long edge yields ten **candidate** stud passages, matching the Midget 1500 parts count. Their centers now align across the block, gasket, head and stud cues. The other 21 visible circular openings are reproduced as unclassified gasket passages. Pixel centers and diameters are recorded in `cad-data.json`; the photo's 563 × 227 px main-body bounds scale to the modeled 355 × 143 mm body. Classifying the ten holes as studs is an inference, and the photo does not verify factory drilling, thread size or fluid routing. The [1977 factory Midget parts book, PDF p. 62](https://www.spridgets.de/downloads/Parts-1977.pdf#page=62) names the 1500 head gasket **GEG373**; a [Midget 1500 replacement listing](https://bpnorthwest.com/mg/head-gasket-spitfire-72-to-80-midget-1500/) cross-references that number. The [head-gasket field page](../head-gasket/) brings the catalog, photo pattern and inspection plan together.

The block inspector also records two independent outside widths: the **metal deck casting across the exposed top face** and the **lower block casting immediately above the oil-pan joint**. An exported direct 142–170 mm deck width or 165–195 mm lower-section width can resize that section in a separate owner STEP. These are validation ranges for this reconstruction, not factory specifications. Either width can be used without the bore-center series. The existing provisional lower section is `P["block_width"] - 20 mm`; the override preserves that relationship, so the connected provisional sump width changes as well. The outer block loft now uses ruled transitions: a 1 mm CAD slice at the lower section reads exactly 172 mm in the public build and 180 mm in a sample owner build, instead of bulging roughly 10 mm past its section width. This is an internal geometry correction, not a newly measured casting contour. A measured width does **not** move the crankshaft, main bearings, front/rear plates, mounts, head, gasket or fasteners, or establish the intervening cast contour. The whole selected-block X/Y/Z bounding box includes side geometry and is not a substitute for either named measurement. Photograph each measuring plane square-on with a ruler and record where the jaws touched; the deck requires an already planned head-off repair.

The [factory Midget 1975 engine-tuning sheet, part 1 PDF p. 17](https://www.spridgets.de/downloads/Midget%201500%20WH%20Teil%201.pdf#page=17) states **7.5:1 compression** for the PE 94J engine. The [factory 1500 engine parts plate, PDF p. 58](https://www.spridgets.de/downloads/Parts-1977.pdf#page=58) identifies **BHM1066** as the 7.5:1 standard piston set for USA and Canada through 1976, with **BHM1066 20** as the .020-inch oversize catalog entry. Neither number identifies the pistons now fitted. The JP1017 drawing used below is cataloged at **9:1**. Its 58.1 mm overall and 32.7 mm pin-to-crown dimensions are a replacement-piston envelope only; the virtual flat crown is not verified for the original 1975 specification or this car. Do not use the CAD to choose a compression ratio, predict valve clearance, or order pistons until the fitted crown and chamber have been identified.

For a second pin-height study, run `build_engine.py --piston-pin-height-comparison 19708 --output-dir comparisons/19708`. The [19708 supplier listing](https://www.classicengineparts.co.uk/products/cep-p-h-19708-std-4-4_cyl_piston_set_19708_for_triumph-cep_p_h_19708_std-4) gives 58.0898 mm overall and 30.1498 mm pin-center-to-crown. The [separate comparison view](./?piston=19708&part=piston_1_replacement_dimensions_provisional) changes only those two dimensions for all four pistons, keeping the crank/rod centers fixed. Its visible crown shape, ring stations, skirt details and the rest of the engine are the provisional public reconstruction. The supplier's explicit low-compression listing is for a 1973 U.S. Spitfire, while its Midget application is broad; this is **not** an identified BHM1066 shape, a verified 1975 Midget fit, or evidence of the pistons in this engine. The comparison STEP and JSON are in `comparisons/19708/`.

The [piston study](../piston-study/#compression-check) now calculates a simplified static compression ratio from directly entered bore, stroke, chamber volume, compressed gasket opening/thickness, signed piston deck clearance and signed crown volume. It leaves every unverified clearance input blank and shows each volume term in the result. At the nominal 73.7 × 87.5 mm dimensions, 7.5:1 corresponds to about 57.43 cc combined clearance volume per cylinder; 9:1 corresponds to about 46.66 cc. That 10.77 cc difference is not a claim about the factory BHM1066 dish alone. The tool neither changes the CAD crown nor identifies a fitted piston.

Each piston inspector now records two direct dimensions separately for that cylinder: overall height from crown plane to skirt bottom (50–65 mm), and pin-center-to-crown-plane height (27–36 mm). Record where the measuring jaws touched and the piston marking in the source note. Export the browser measurement log, then pass it to `build_engine.py --measurements` for a separate owner STEP and web model. Either dimension can be supplied alone; only that piston's envelope changes. The builder rejects a combination that would leave less than 15 mm of skirt below the pin center. This changes the nominal top and skirt planes and moves the provisional ring stations with the pin-to-crown height; it does not reconstruct a dish, valve relief, real ring grooves, skirt cam shape, compression ratio, or piston-to-head clearance. Do not use the owner build to select parts or machining dimensions without measuring those interfaces.

A [Classic Engine Parts low-compression replacement listing](https://www.classicengineparts.co.uk/products/cep-p-h-19708-std-4-4_cyl_piston_set_19708_for_triumph-cep_p_h_19708_std-4) gives 58.0898 mm overall height and 30.1498 mm pin-center-to-crown height for 19708, with an explicit 1973 U.S. Spitfire 1500 7.5:1 application and a broad Midget 1500 alternative listing. [Deves' ring application chart](http://www.deves.com/devesrings/cars_MG.php) separately names AE 19708 and 20139V1 for 1975–80 Midget 1500 engines. The 19708 pin-to-crown height is about 2.55 mm shorter than JP1017's 9:1 comparison dimension, equivalent to about 10.9 cc across a nominal 73.7 mm bore if the pin position is held fixed. Neither listing establishes equivalence to BHM1066 or the fitted piston, and neither gives a dimensioned crown profile. The public CAD therefore retains the explicitly labeled JP1017 envelope; the alternative is recorded in `cad-data.json` for comparison rather than applied as an assumed factory shape.

The piston model now uses the [JP Pistons JP1017 replacement drawing, PDF p. 162](https://www.norndaautomotive.com.au/images/technical-information/2025_JP_Pistons_catalogue-compressed.pdf#page=162) for the Midget Mk III 1493 cc. It gives **58.1 mm overall height**, **32.7 mm crown-to-pin-center distance**, a **20.64 mm pin**, two **1/16-inch compression rings**, and one **4 mm oil-control ring** per piston. The [factory specification, PDF p. 11](https://www.spridgets.de/downloads/Midget%201500%20WH%20Teil%201.pdf#page=11) also lists Grade F/G cylinder bores and piston-bottom diameters, plus **0.051–0.076 mm top** and **0.005–0.041 mm bottom** diametral skirt clearance. The CAD uses midpoint Grade G bore/piston values as one representative standard-size pairing, including a slight skirt taper; this is not identification of the four fitted pistons or their wear. The STEP separates four hollow piston shells, four hollow pins, eight compression rings, and four oil rings. Drawn groove depths and positions, pin bosses, hollow underside, ring gaps and skirt shape remain estimates. The current provisional 225 mm deck-to-crank distance yields about 2.55 mm crown-below-deck at modeled top dead center; that is a consequence of unverified block layout, not a factory deck-clearance claim. Identify the actual pistons and measure deck position before using their modeled height for service work.

The [factory rocker-shaft exploded drawing, part 3, PDF p. 7](https://www.spridgets.de/downloads/Midget%201500%20WH%20Teil%203.pdf#page=7) guides seven separately selectable study groups: valve springs, rocker pedestals, pedestal fasteners, shaft, eight arms, eight adjuster screws/locknuts, and eight pushrods. The valve heads retain their documented diameters. The [factory specifications, part 1, PDF p. 12](https://www.spridgets.de/downloads/Midget%201500%20WH%20Teil%201.pdf#page=12) add a 14.30–14.33 mm rocker-arm bore, four working outer-spring coils and 34.2 mm outer-spring fitted length. The helical springs and arm bores now use those figures. The manual prints 0.5607–0.5612 in for the rocker shaft beside an inconsistent 14.27–14.35 mm metric range; CAD uses 14.2418–14.2545 mm converted from the inch values and records the discrepancy in `cad-data.json`. Shaft length, lever profiles, wire section, spring seats, fastener dimensions, pushrod paths and all center locations remain provisional. The model cannot establish replacement-part fit.

The [factory Midget specification, PDF p. 11](https://www.spridgets.de/downloads/Midget%201500%20WH%20Teil%201.pdf#page=11) gives crankshaft end float of **0.006–0.014 in (0.1524–0.3556 mm)**. The [Moss Midget catalogue, PDF p. 241](https://www.moss-europe.co.uk/content/files/pdfs/moss-europe-sprite-midget-catalogue-issue-25.pdf#page=241) lists standard BHM1366 thrust washers as a pair, with oversizes available. The [shared 1500 workshop manual](https://triumphspitfire.com/wp-content/uploads/2023/08/Triumph-Shop-Manual.pdf) places one upper half-washer on each side of the rear main bearing, thrust faces toward the crank, and permits a dial gauge or feeler gauge for the end-float check. The CAD exposes the two washers separately. Their 60 mm inside diameter, 80 mm outside diameter, 2.3 mm thickness, plain face and 0.5 mm visualization gaps are estimates, **not** dimensions for selection or repair. Either washer inspector can record the single measured end-float value for the whole crank and compare it with the factory assembly range; the log stores one shared reading and does not resize the mesh or diagnose wear. Record the measurement setup and inspect the fitted washers and crank before choosing replacements.

The [factory specification, PDF p. 12](https://www.spridgets.de/downloads/Midget%201500%20WH%20Teil%201.pdf#page=12) gives camshaft front/rear journal diameters of **49.93–49.95 mm**, a center journal diameter of **49.90–49.92 mm**, tappet outside diameter **20.30–20.32 mm**, tappet length **44.45 mm**, and a single **0.375 in × 62-pitch** timing chain. Those dimensions now drive the separate cam, eight followers and chain. The same page gives 0.04–0.09 mm front/rear and 0.07–0.12 mm center diametral cam clearances; the model uses their midpoints with the matching journal diameters to derive a roughly 50.005 mm tunnel bore. The manual also gives 0.12–0.216 mm cam end float, recorded for inspection but not animated. The [Midget 1500 internal-engine plate, PDF p. 33](https://mossmotors.com/media/wysiwyg/catalogpdf/spm_catalog_web.pdf#page=33) establishes the retainer, sprockets, lockplate, two cam bolts and tensioner as distinct components. The CAD exposes them individually along with angled pushrods and an illustrative block tunnel.

Matching supplier photographs suggest **20 crank and 40 cam sprocket teeth**; that count is visually inferred, not a measured factory specification. A [matching 119389 replacement listing](https://classiccarparts.co.nz/MG-Midget-MGB-GT-Roadster-V8-18v-18G-Parts-Spares-engine-electrical-brakes-performance-upgrade-trim-NZ-Auckland-stockist-seller-buy-repair-restoration/MG-Midget-998-1098-1275-1500-leyland-Parts-Spares-engine-electrical-brakes-performance-upgrade-trim-NZ-Auckland-stockist-seller-buy-repair-restoration/triumph-mg-timing-chain-sprocket.-crankshaft-simplex-35mm-%28single-row%29-119389) explicitly says **35 mm crank bore**, which now scales the model’s front crank nose and gear interface. Solving an ideal taut 62 × 9.525 mm chain path around 20/40-tooth pitch circles gives a **149.02 mm center distance**. The CAD keeps a provisional 65 mm sideways cam offset and derives its height from that distance. This is a geometric reconstruction, not proof of the actual block centers: the tensioner changes chain path, and the fitted gears have not been inspected. The cover and front plate were widened to clear the larger timing drive; their outside edges, screw pattern, gear tooth profile, cam phase, chain plate shape, tensioner pivot, journal stations, pushrod length and tunnel casting all remain provisional. Use the [timing-drive study](../timing-drive/) to record the real assembly before timing or replacing anything.

The [Midget 1500 cylinder-head parts plate, PDF p. 34](https://mossmotors.com/media/wysiwyg/catalogpdf/spm_catalog_web.pdf#page=34) and an assembled 1500-family head photograph show the eight valve springs in **one lengthwise row**. The previous two-row CAD arrangement was wrong. Valves, springs, rockers and pushrods now share the corrected layout. The [external-engine plate, PDF p. 32](https://mossmotors.com/media/wysiwyg/catalogpdf/spm_catalog_web.pdf#page=32) lists ten head studs (eight short, two long), ten nuts and ten washers. The model now exposes these as separate parts and aligns their approximate stations through the block, gasket and head. Stud coordinates, thread, installed projection and which two are long remain unverified; these holes must never be used as a machining template. Bore centers now follow a separately documented gasket-image comparison, still not a factory boring drawing.

The same Midget 1500 head plate lists eight valve guides, eight upper spring collars, eight lower collars and sixteen split cotters. These are now separate selectable model groups. I also corrected a previous modeling inconsistency: the valve stems had ended below the spring tops, and the rocker tips missed the stem ends. They now meet the collar/cotter stack and rocker contact area. Exact guide fits, spring-seat shapes, stem lengths, cotter taper and valve centers are **not** dimensioned by that plate. Their geometry is a topology and access study, not a valve-service drawing.

An [inlet replacement valve listing](https://www.angloparts.com/en/part/012.158) and [exhaust replacement valve listing](https://www.angloparts.com/en/part/012.073) for the Midget/Spitfire 1500 both give **108.2 mm overall length**; their stated stem diameters are **7.9 mm inlet** and **7.8 mm exhaust**. The model now uses those comparison dimensions while retaining the factory-manual valve-head diameters. The position of each valve in this particular head is still provisional, as is its rocker clearance and fitted part identity. These supplier dimensions should be confirmed against a removed original before a fitment decision.

A [North American Midget 1500 inlet-guide listing](https://www.fwthornton.co.uk/vag-154-inlet-valve-guide-suitable-for-mg-midget-1500-249006) gives **52.4 mm length, 12.75 mm outside diameter and 7.97 mm inside diameter**. The Moss head plate lists one stock guide type for all eight positions. The CAD uses the dimensioned guide as a comparison envelope for eight sleeves. The listing does not establish this car's installed projection, finish-reamed bore, interference fit or exact guide variant; those remain owner-car measurements.

The cylinder-head envelope now has an open rocker recess, four support pads, shallow side reliefs and four side-entry spark-plug silhouettes. A [photograph of a bare 1500-family head](https://rimmerbros.com/Item--i-GRID005547) guides the recess and cast reliefs, while the owner overview shows the leads on the corresponding engine side. The pictured loose head is not this car's verified casting. Recess depths, plug stations and outside surfaces remain estimates; the actual plug number, reach and tool clearance need direct confirmation.

A [photographed 1500-family exchange head deck](https://www.classicmachineshop.co.uk/product-page/cylinder-head-triumph-1500-reconditioned-unleaded-spitfire-mg-midget) shows four elongated openings beside the combustion chambers. The CAD now cuts four shallow, round-cornered recesses on that side, each **17 × 51 × 15 mm as an unmeasured visual estimate**. Their provisional centers follow the four bores; the existing gasket study has two adjacent edge openings per cylinder. This establishes a recognizable deck-face topology only. The photographed exchange head is not identified as this car's fitted casting, and the aperture shape, internal route, depth and relationship to the actual gasket must be checked directly during a planned head-off repair. Never use this face for machining or gasket selection.

A [nearly square-on recessed 1500 head-gasket photo](https://philipsclassics.be/products/gasket-cylinder-head-reccesed-spitfire-1500-mk4-midget-1500) provides an envelope check: its outside width is about 1.9 times a bore opening. An [Ajusa 10019300 replacement listing](https://www.fabucar-shop.de/AJUSA-Dichtung-Zylinderkopf-10019300/KFZ-6816182) gives **143 mm width**, 365 mm length, 1 mm thickness and a 74 mm aperture; [Triumph replacement catalogues](https://lococlassics.nl/wp-content/uploads/2018/12/Triumph-Spitfire-MKI-IV-1500.pdf) cross-reference its AJM373 family to the recessed-bore 1500, including the Midget. The [near-square-on product image](https://www.niparts.com/Graphics/full/DATA_6/1209361.jpg) visibly groups the four bores as two closer pairs. Median image centers are at X = 97.5, 224, 362 and 489 px. Scaling the 579 px full gasket length by the listed 365 mm gives adjacent intervals about 79.7, 87.0 and 80.1 mm; scaling by the nominal 74 mm aperture instead gives about 78.7, 85.8 and 79.0 mm. The public CAD uses rounded **79.5 / 86.5 / 79.5 mm photo-derived intervals**, replacing the equally spaced 82.5 mm guess. This shifts the bores, pistons, rods and crank throws together, not the provisional bearing stations or casting faces. The same image and listing support a 143 mm width, roughly 355 mm main body and 10 mm rear tab projection for the gasket silhouette, producing a 365 mm overall model length. The tab shape, 1 mm listed free thickness versus installed compression, exact aperture and stud centers, orientation and fitted gasket remain unverified. The provisional head remains 148 mm wide and the block deck 150 mm; their centerlines are offset 15 mm from the bore axis as a photo interpretation. These image measurements cannot guide drilling, gasket selection or machining.

`P` at the top of the build script holds **provisional** geometry: bore pitch, casting envelopes, deck height, axial journal widths, piston crown height, rod cross sections, and sump dimensions and rocker-cover height. The STEP part names distinguish these provisional castings. Factory exploded drawings guide assembly topology, but are not scaled enough to supply those values.

The head gasket is now a separate selectable interface with four nominal-bore openings. Ten regularly placed openings in one near-square-on supplier image are candidate stud passages, matching the catalog count; another 21 openings are modeled without assigning their function. All centers and diameters are photo estimates, and the exact factory pattern, fluid routing, side orientation, fire rings and compressed thickness are not verified. The CAD is not a gasket, drilling or fastening template. The oil pan now has a separate flange and tapered basin instead of one rectangular box. This makes the assembly relationship legible, but the pan profile and mounting-hole positions are still placeholders. The viewer's floor grid is 50 mm per square in model coordinates; grid scale does not validate any provisional outer surface.

The [Rimmer Spitfire parts catalogue](https://rimmerbros.com/images/PDFs/Spitfire.pdf) explains that all 1500 blocks use a recessed bore lip and a matching head gasket identified by a small tab at the rear. A [replacement gasket listing explicitly includes the MG Midget 1500](https://classiccarpartsaustralia.com.au/Triumph-TR2-tr3-tr3a-tr4-tr4a-tr5-tr6-tr7-spitfire-herald-gt6-vitesse-2.5-2000-2500-stag-dolomite-1300-1500-Parts-Spares-engine-electrical-brakes-performance-upgrade-trim-NZ-Auckland-stockist-seller-buy-repair-restoration/triumph-dolomite%2C-sprint%2C-toledo-hawkswood-classic-car-parts/gasket-set-cylinder-head-recessed-block-triumph-1500-mg-midget-1500.-ajm1195?limit=100&order=ASC&sort=pd.name). Four shallow deck recesses and a rear gasket tab now make that interface visible in the study. The recess diameter and depth, gasket outline and tab position are **not measured**. Confirm the block and gasket type on this car before ordering parts; the model is not a machining or gasket-cutting pattern.

The block's lower crankcase is now open beneath shorter cylinder barrels. Three separate lower main-bearing caps and six cap-bolt silhouettes follow the [factory crankshaft assembly drawing, part 3, PDF p. 4](https://www.spridgets.de/downloads/Midget%201500%20WH%20Teil%203.pdf#page=4). A [photograph of a stripped Midget/Spitfire 1500-family block](https://www.ebay.com/itm/206168978107) helped check the open-cavity topology and side-face complexity; that other block is not this car and its photo is not republished. The cavity dimensions, cap spacing and bolt coordinates remain provisional, and the actual bore-barrel depth is not established by the source photo.

The [Midget 1500 internal-engine plate, PDF p. 33](https://mossmotors.com/media/wysiwyg/catalogpdf/spm_catalog_web.pdf#page=33) identifies separate rod-bearing sets, four connecting rods, eight rod bolts and four wrist-pin bushes. The CAD now separates four lower rod caps, eight bearing half-shells, eight bolt silhouettes and four small-end bushes, so an underside view can show how a rod is retained on a crankpin. A [fitting aftermarket rod](https://www.limora.com/en/con-rods/539099/) lists 146.05 mm center length, 51.34 mm big-end housing bore, 22.15 mm small-end bore, 22.78 mm big-end width and 21.6 mm small-end width; those values scale the comparison envelope while the factory range still governs center distance. The listed rod is an H-beam replacement, **not the factory rod or this car's verified rod**. Cap outer shape, split details, bolt locations, shell thickness, bearing grade and exact fitted hardware remain provisional. The STEP cannot select bearing size or torque.

The owner's existing engine-bay photos show the red rocker cover in IMG_6797, IMG_6853 and IMG_6856. A replacement AJM414 gasket (AJUSA 11007400) is listed at **360 × 110 mm**. The model uses that supplier footprint as an in-place scale anchor, with an inferred 5 mm lip overhang. The cover is now a hollow loft with a lower lip, narrowing stamped shoulders, two shallow transverse stampings, a center panel and separate fasteners. Its height, wall thickness, shoulder contour, stamping heights and fastener positions remain provisional. IMG_6856 shows a dark cap at the cover opening; IMG_6893 shows a silver two-grip cap stamped “CAUTION REMOVE SLOWLY” in that area. The later photo does not prove the silver cap is fitted to the cover rather than resting there. The CAD now follows the earlier dark silhouette only. Its diameter and retention are unverified placeholders, not fitment dimensions.

The cover hold-down group now separates the two stud shafts, washer stacks and hex nuts, so the user can select the mounting hardware as an assembly. This is an *early-arrangement study*, not a claim that the photographed car has that exact stack. IMG_6908 gives a closer view of an adjacent casting and fasteners beside the red cover. That image does not establish whether the visible cast surface is the head or a neighboring manifold, nor does it resolve the hardware size or casting marks. The part inspector opens a plain-language function, fastening and access card on selection; the detailed dimension log is folded away until needed.

The distributor and alternator are separate recognition models based on visible components in IMG_6797 and IMG_6856. The distributor includes a body, cap and five terminal towers: four plug positions and a central coil-feed position. The alternator now has a finned case and continuous shaft, with a separately selectable cooling fan, lower pivot bracket, slotted adjusting link and a **single** pulley. The former study incorrectly showed two alternator pulleys at different offsets; that duplicate was removed. [Rimmer's Midget 1500 alternator listing](https://rimmerbros.com/SubCategory--MG-Midget-1500-Alternators--m-24525) identifies lower bracket 147899, adjusting link 156464, fan AAU3956A and AEU1238 as a **2.5-inch pulley with a 3/8-inch groove designation**. The [Moss alternator plate, PDF p. 96](https://mossmotors.com/media/wysiwyg/catalogpdf/spm_catalog_web.pdf#page=96) also separates front fan and pulley. The 3/8-inch designation names a belt class; it is not a measured groove-mouth width. The CAD now turns a visible V profile with catalog-comparison outside diameter and a separate opening around the virtual shaft. It uses a 9.525 mm mouth opening as a **modeling choice** and gives the water-pump sheave a visually matching groove. Both sheaves' true mouth widths and depths, axial widths, bores, stations and fitted identities are provisional. Case size, brackets, bolt centers, fan form and axial offsets are also **provisional**. The browser CAD inspector links these parts back to the owner's photo locator. Other visible parts should be compared in the same plane after accounting for perspective, never scaled by a single raw pixel ratio across different depths.

[Rimmer's photograph of lower bracket 147899](https://rimmerbros.com/Item--i-147899) establishes a single central pivot lug and two engine mounting holes. The earlier CAD incorrectly put two ears on the bracket. The revised model puts two ears on the alternator case and one lug on a connected bracket casting. The casting now has an open triangular side web instead of a rectangular pillar, following the visible topology in Rimmer's photograph and the [Moss Europe exploded view, printed p. 182](https://www.moss-europe.co.uk/content/files/pdfs/moss-europe-sprite-midget-catalogue-issue-25.pdf#page=240). The web's section and opening are visual estimates, not dimensions. A comparison [MGOC installation photo and procedure](https://www.mgocspares.co.uk/blog/1439/dynamo-to-alternator-conversion-triumph-spitfire-mkiii) show the bracket foot and fixing heads accessible on the **front face** of the engine plate. The previous virtual foot sat behind that plate. It now sits ahead of the plate, with its support routed around the plate edge, and the plate has matching candidate clearance holes. [Rimmer's Midget 1500 listing](https://rimmerbros.com/SubCategory--MG-Midget-1500-Alternators--m-24525) specifies GHF103 **5/16 UNF × 1 in** screws; the installation procedure specifies two GHF332 spring washers. Both screws and washers are separately selectable CAD parts. The virtual bracket foot now has a 22 mm clearance cut for the modeled hex-head sweep in either direction; that cut is an internal geometry accommodation, not a measured feature of bracket 147899. The screw lengths, diameters and counts are catalog supported; **hole centers, bracket outline, backing threads, access angle and installed hardware are unmeasured**. This is a service-layout study, not a drilling pattern or a verified removal path.

[Rimmer's 156464 product photograph](https://rimmerbros.com/Item--i-156464) shows a fixing tab bent away from the slotted arm and a large lifting eye beside that slot. The old CAD link was a flat plate with one small hole in place of the lifting eye. The new connected solid models both holes, the slot and the offset tab. Its bend height and placement remain estimates. It clears the modeled alternator, pulley, fan and front plate, but still crosses approximately 360 mm³ of the provisional timing-cover crown. The virtual slotted arm begins at axial station 203 mm while the modeled alternator upper ear ends at 183 mm, leaving a 20 mm non-mating gap. Moving the whole link 20 mm rearward cleared the cover but intersected the engine front plate and alternator ear, so that trial was rejected. The browser worksheet now records the actual upper-ear/link plane, tab/cover plane, bend offset, eye-to-slot distance and slot dimensions; these observations are not yet applied to the STEP. A [Spitfire 1500 exploded alternator plate, PDF p. 102](https://rimmerbros.com/images/PDFs/spitfire.pdf#page=102) confirms the slotted link meets the upper ear but supplies no Midget-specific axial dimensions. Do not use this virtual link to judge clearance or fastener access on the car.

IMG_6894 of the actual car clearly separates a dark rear housing, dark middle band and open silver front casting. The former alternator CAD was one uniform solid cylinder, hiding those visible layers. The reconstruction now exports the rear cover, middle band and vented front frame as separate STEP and browser parts, and the [photo locator](/cars/1975-mg-midget/locator/?view=altclose) marks each section on IMG_6894. Cast ribs, windows, bearing boss, rear terminals and case-section lengths are still visual estimates. IMG_6976 now identifies the fitted unit as a Bosch AL298X remanufactured alternator. IMG_6972 shows that the first CAD split still made its silver cast sections too thin and its dark rear cover too long. The revised CAD uses deeper silver shells on both sides of the stator band and a shorter dark rear cover. Those section lengths, ribs and vents are photo-derived silhouettes, not measured AL298X dimensions or certified internal construction.

The [Bosch AL298X product photographs](https://www.boschautoparts.com/p/remanufactured-alternators-al298x-) provide a front-on view with two broad side openings, one shorter lower opening, a three-spoke bearing boss and an upper ear. The earlier five-aperture virtual face contradicted this image; the STEP now follows the three visible openings. Bosch's side view and IMG_6972 also support fewer broad cast lands than the former eightfold rib pattern; the model now uses four comparison ribs on each silver shell. Their number, clocking, radii and axial profiles are not measured on the fitted unit. The catalog photo has no scale and shows a unit without an installed pulley; verify the owner's fan, pulley, ear clocking and bracket stack on the car. The IAT replacement-stator comparison diameter and candidate pivot spacing remain separate provisional inputs; neither becomes a Bosch drawing through this face correction.

Bosch also photographs an asymmetric molded rear connector housing. It is a separate selectable comparison part in the CAD, with a shallow empty connector recess. IMG_6972 does not show this car's rear electrical face, so the housing clocking, outside size, connector retention, individual terminals, wire positions and clearance are unknown. The 3D cavity cannot be used as a wiring diagram; inspect the installed rear before an alternator project.

[NAPA's AL298X listing](https://www.napaonline.com/en/p/BSHAL298X)
simultaneously says no pulley is included and supplies a
71 mm six-groove serpentine pulley specification and 22SI series label. Those
fields conflict with the single V-groove pulley photographed on this car and
the Bosch 1V catalog description. They are not a dimensional input to this
STEP. The alternator guide records the discrepancy so a catalog search cannot
silently override the owner photograph.

The alternator inspector can now record separately the front-case outside diameter, all four visible axial section lengths, shaft-to-pivot distance, front and rear ear thicknesses, clear inside-ear gap, and connector projection. Each saved value keeps evidence type and a measurement-point/source note and can be exported with the CAD log. Direct case diameters, section lengths, shaft-to-pivot distance, lower-ear thicknesses and clear gap can reshape a separate owner STEP build, as detailed below. Connector projection and bolt access remain evidence records and are listed as unapplied in the provenance file. These dimensions do not establish the hidden stator diameter or bore, absolute engine station, installed bracket or belt lane; the public browser model stays at its comparison sizes until separately rebuilt.

The first split assembly reused an undersized **94 mm outer casing**. An earlier pass used a generic [17/18ACR replacement stator](https://www.yourex.eu/stator-12v-45a-18acra115-45/) at 114 mm OD, 83 mm ID and 25 mm width because [SC Parts lists a 17ACR-type unit for Midget 1500 models](https://www.scparts.co.uk/en/lucas-three-phase-alternator/20198/). That comparison has been superseded for the fitted Bosch AL298X. [IAT's replacement-stator catalog, PDF page 4](https://iat-usa.com/wp-content/uploads/2017/07/IAT_Stators_Catalog_2017.pdf#page=4) lists part **07118** for AL298X at **108.25 mm OD, 73.95 mm ID, 20.55 mm lamination stack and 36 slots**. The current CAD uses its outside and inside diameters. Its **25 mm visible dark-band gap remains a photo estimate**: a lamination-stack thickness is not the distance between visible silver case seams. IAT also lists a 35.60 mm exposed-stack dimension without defining it as that case gap. The installed remanufactured stator has not been inspected. The unmeasured silver frame remains at 124 mm OD. The larger envelope and pivot-bolt clearance study led to the alternator center moving 28 mm farther outboard from the original x=150 mm to x=178 mm in the virtual engine, with pivot ears and bracket lug moved to match. This is a clearance estimate, not a measured mounting station; the bolt might be installed in the opposite direction on the real car. Measure its body, pulley offset and mounting centers before relying on this comparison for replacement or withdrawal planning.

**Internal-parts cross-check.** [IAT's rotor catalog, PDF page 10](https://www.iat-usa.com/wp-content/uploads/2017/07/IAT_Rotors_Catalog_2017.pdf#page=10) lists Lucas 17/18ACR replacement rotor 17402 at **83 mm OD** and includes Lester 14029 in its broad interchange list. That rotor cannot fit the **73.95 mm ID** of Bosch-family stator 07118: it exceeds the opening by 9.05 mm in diameter. These are alternative catalog families, not an assembled rotor–stator pair. The public CAD therefore does **not** add that Lucas rotor inside its AL298X-compatible stator. A complete-alternator cross-reference cannot identify the components inside this car's remanufactured unit; inspect the fitted core before choosing internal repair parts.

**North American mounting correction.** The [factory Midget 1500 parts list, printed p. 183](https://www.spridgets.de/downloads/Parts-1977.pdf#page=183) includes bracket 147899 in the common group and adds CHA304 for USA and Canada. It assigns pivot spacer 147483 and bolt HB839 to cars outside USA and Canada, and distance tube UKC3128 with bolt HB841 to USA and Canada. The catalog gives no usable dimensions or placement drawing for CHA304, UKC3128 or HB841. The public 147899-style CAD and virtual tube/bolt are therefore topology and access comparisons, **not a reconstruction of the period North American stack or proof of what is fitted to this Bosch AL298X car**. Photograph the assembly and directly measure its parts before using this model to plan a repair.

A [used-parts listing for CHA304](https://robertpieces.com/en/used-parts-for-british-cars/1919/alternator-bracket-mg-midget-1500-detail) has a photograph whose handwritten tag and image filename appear to say **CHA204**, while the product SKU says **CHA304**. The mismatch makes that photograph unsuitable as geometry evidence. IMG_6971–6972 show portions of the installed lower mount but not the full bolt/tube/bracket relationship. A square-on photograph of each side or a dimensioned original part is still needed before drawing CHA304.

[Rimmer's Midget 1500 alternator catalog](https://rimmerbros.com/SubCategory--MG-Midget-1500-Alternators--m-24525) lists BH605401A as a **5/16 UNF × 5 in** pivot bolt, and its [147483 spacer listing](https://rimmerbros.com/Item--i-147483) specifies one spacer. A [replacement LRA100/17ACR supplier](https://classiccarpartsaustralia.com.au/Mini-parts-spares/alternator-17acr-with-fan-pulley.-left-or-right-hand-fitting-lra100-gxe2206) gives **85 mm between mounting lugs**. The candidate CAD now uses that inner-ear gap while keeping the front pulley plane fixed: the rear cover and rear ear move back, and the tube between rear ear and bracket lug becomes **73 mm**. This is the length of a virtual gap, **not a catalog spacer dimension or a measurement of this car**. The separate model also shows a nominal 7.94 mm × 127 mm bolt and a selectable washer/nut cue. Bolt axis, head side, withdrawal clearance, thread length, washer and nut details remain unverified. This assembly can teach the order of parts to inspect; it cannot yet specify hardware or removal clearance for this car.

The browser's alternator mounting study steps through the fitted-unit comparison, upper link, bracket screws, pivot bolt, spacer and pulley. Each step selects and frames an existing CAD part; it does not animate an asserted removal path. The pivot bolt has a separate model-only withdrawal slider. The linked [replacement preflight](../workshop/#alternator-replacement) records the actual identity, hardware order, wiring and withdrawal space needed before a repair decision.

[RatSport's replacement ACR](https://www.ratsport.com/lucas-acr-type-high-output-replacement-alternator-c2x9667761) gives an **approximate 91 mm pivot-center-to-pulley-center distance**. The earlier virtual pivot was only 77 mm from the shaft. The two alternator ears, lower bracket lug, spacer, bolt and retainer now share a center **91 mm below the virtual shaft**. The bracket's support was rerouted around the moved bolt and the modeled non-mating intersections rechecked. A [different replacement 17ACR supplier](https://www.rotatingelectrics.co.uk/products/17-acr-alternator-lucas-type-12v-110178-lra100-classic-vintage-wood-auto-16001) gives **164 mm total length**. The virtual rear-cover-to-pulley envelope is now roughly **171 mm** after aligning the study's three groove planes; this difference is another reason to measure the fitted unit and its pulley projection. These are comparison dimensions for replacement units; they do not establish the alternator fitted to this car, its mounting-foot shape, shaft station or installed clearances.

Selecting the pivot bolt in the browser exposes a **0–127 mm withdrawal slider** for the public rear-head comparison. A direct 50–180 mm under-head length and an observed head side can now reshape a separate owner STEP. Its slider uses that length and withdraws toward the modeled head side; if a saved observation contradicts the loaded model, the slider is disabled until the matching build is opened. `audit_pivot_path.py --measurements` checks the complete straight swept volumes against thirteen named virtual groups, including the distributor body, side housing and vacuum capsule, in the selected direction. This is an internal geometry check, **not a fitted-car clearance**. The builder rejects a bolt too short for the measured ears and provisional spacer/retainer stack. The inspector separately compares direct head-side free space with direct bolt length; a positive margin remains preliminary because bodywork, wires, hoses, tools, hardware details and actual withdrawal angle are not established.

The [1975–76 Midget 1500 manifold parts plate, PDF p. 47](https://mossmotors.com/media/wysiwyg/catalogpdf/spm_catalog_web.pdf#page=47) identifies separate inlet and exhaust castings, their shared gasket and hardware, the carburetor connection and the exhaust downpipe joint. The CAD now has two independent manifold studies with branching runners and visible flanges. Their ports, stud centers, gasket faces, cast contours and even the fitted variant remain unverified. The photographed air cleaner and Zenith-Stromberg were moved toward the middle of the engine, matching their relative position in IMG_6856 more closely. That location is still a perspective-based estimate, not a surveyed mounting coordinate.

The [GEG742 gasket supplier](https://classiccarparts.co.nz/Austin-Healey-3000-Sprite-BN7-BT7-BJ7-BJ8-Parts-Spares-engine-electrical-brakes-performance-upgrade-trim-NZ-Auckland-stockist-seller-buy-repair-restoration/gasket-exhaust-flange-midget%2C-spitfire-1500-52mm-id%2C-70mm-hole-centre-geg742?limit=75) specifies a **52 mm opening** and **70 mm between mounting-stud centers** for the Midget 1500. Its photograph shows three holes; the [MGOC parts catalogue](https://www.mgocspares.co.uk/DocumentHandler/136685/mgoc-spares-midget-catalogue-pdf) independently lists GEG742 at the manifold-to-downpipe joint and three special nuts. The former solid round CAD flange is now an open triangular three-hole comparison, and the thin gasket is a separately selectable part. The 70 mm equilateral hole pattern, triangular outline, 9 mm model holes, 1.5 mm gasket thickness, flange clocking and downstream position are study choices because the listing gives only one center-to-center distance, not a dimensioned drawing of all three centers or the fitted casting. Check the real flange and measure all three spacings before planning fastener access or choosing a gasket.

The gasket inspector accepts a direct opening and independent A–B, B–C and C–A hole-center measurements. A separate owner build solves the three-hole triangle, redraws both the gasket and manifold flange, and rejects triangles or bore clearances that cannot work. The outlet sleeve follows the recorded opening as a comparison relationship. The gasket's exterior is a generated envelope around the bore and stud pads, not a traced perimeter. Thickness, hole diameters, actual stud positions in the car and fitted flange clocking still require direct evidence.

The owner's IMG_6856 shows a large black box behind the red cover. Its shape and position match the separate [Moss Midget 1500 heater assembly, PDF p. 39](https://mossmotors.com/media/wysiwyg/catalogpdf/spm_catalog_web.pdf#page=39); IMG_6892 now shows SMITHS molded into that casing and its hose/outlet layout, supporting the heater identification; the exact model still needs its number. The CAD previously mislabeled this box as the engine air cleaner and drew an unsupported duct toward the carburetor. That duct was removed; the separate metal air cleaner and coupling visible in IMG_6885–6887 are now modeled as photo-reference parts. The [US air-filter parts plate](https://www.angloparts.com/en/spare-parts/mg/midget-and-sprite/engine/carburettors/d/air-filter-and-controls-usa-iynivwkkdorbpycxmtjwx) shows a separate intake assembly, while the new photos locate the fitted case and coupling but do not establish their exact numbers or dimensions. IMG_6839 confirms a Zenith-Stromberg carburetor and yellow damper cap. Its body now has an open nominal 38.1 mm 150-series throat; the dashpot cover, diaphragm, piston/needle and float bowl are separate selectable parts following the [factory CD4 exploded view, PDF p. 26](https://triumphwedgeowners.org/wp-content/uploads/2022/04/zenith_stromberg_factory_tuning_manual_-_complete.pdf#page=26). The former solid cone was replaced by a rounded hollow cover with a square-edged flange and two selectable screw-head markers guided by IMG_6958; centers, threads and hidden fasteners remain unmeasured. The [Moss carburetor plate, PDF p. 42](https://mossmotors.com/media/wysiwyg/catalogpdf/spm_catalog_web.pdf#page=42) distinguishes 1975–76 Federal C3754 and California C3755 carburetors. The fitted tag and every exterior CAD dimension remain unverified. The rear box appears roughly three times as wide as the red cover in IMG_6856; the 110 mm gasket width gives an **approximate 330 mm model width**. Perspective makes this a rough estimate. Heater casing, outlet, mount and carburetor coordinates remain provisional; the carburetor tag and calibration still need direct confirmation.

The [factory Midget 1500 air-cleaner plate, PDF p. 122](https://www.spridgets.de/downloads/Parts-1977.pdf#page=122) lists North American 1975 assembly **CHA295**, the later **CHA554**, and one **GFE1060** element. Its exploded drawing shows a flat panel between the outboard cover and carb-side backplate. IMG_6885–6887 show a similarly arranged weathered case and two visible latches, but do not prove the fitted part number. The revised CAD uses a **100 × 150 × 280 mm comparison case** (X outboard depth, Y vertical height, Z length) and a **30 × 120 × 250 mm panel study**. These are visual envelopes, not factory or owner measurements. The cover and backplate are separate hollow solids; the element is between them, with two latch studies and a provisional intake opening. The five-step browser view moves those pieces outward for inspection. It is not a verified withdrawal path. Direct case and removed-element measurements can be exported for a separate owner STEP build, with the element accepted only when its dimensions fit the recorded case clearance. The split, seal, sheet gauge, clip shapes, inlet, bracket and installed mounting coordinates remain unverified.

The front cooling group separates the water-pump housing, pump, thermostat housing and filler-plug position ahead of the head/block. The water-pump housing now exports as one fused casting solid instead of 16 touching sub-solids; this corrects CAD topology without adding dimensional evidence. [MGOC's Midget 1500 parts listing](https://www.mgocspares.co.uk/parts/mg/midget/cooling/water-pump-fan-thermostat/1500cc) establishes those component relationships and names the separate pump and thermostat gaskets. A [138702 housing gasket photographed beside a ruler](https://classiccarparts.co.nz/gasket-triumph-mg-1500-water-pump-housing-to-block-gasket.-138702) now scales a separate **roughly 94 × 61 mm** gasket and matching rear housing face, with three holes and two coolant openings. The traced face is provisionally placed at the front of the head, consistent with the [period Spitfire 1500 parts catalog](https://www.ovtc.net/uploads/9/5/1/6/9516577/spitfire_mk_iv-1500.pdf) calling 138702 the gasket between pump and cylinder head; later supplier descriptions vary between head and block. The photograph is not a replacement-cutting pattern. A second [138701 pump gasket photographed beside a ruler](https://classiccarparts.co.nz/gasket-triumph-water-pump-138701) scales a separate **roughly 91 × 81 mm** pump joint with a 65 mm central opening and three holes. Its contour now informs the pump flange and housing seat. These two gasket photographs improve recognition geometry; neither is a manufacturing drawing or proof of the fitted pump variant. The [Moss Europe Midget 1500 cooling plate, printed pp. 136–137](https://www.moss-europe.co.uk/content/files/pdfs/moss-europe-sprite-midget-catalogue-issue-25.pdf#page=194) identifies three separate housing-to-cylinder-head bolts: upper BH605221 at 2¾ inches, lower-left BH605191 at 2⅜ inches, and lower-right BH605181 at 2¼ inches, each 5/16 UNF with a lock washer. The drawing provides a useful position and length checklist for a planned inspection. A trial CAD placement of these bolts intersected the virtual pump, exposing an unverified relationship between the current head flange and pump seat. [Rimmer’s 144297A housing photograph](https://rimmerbros.com/Item--i-144297A) shows distinct machined interfaces but does not establish their angle; it is a topology reference, not a scaled drawing of this car. The STEP therefore omits the housing-to-head bolts until the fitted casting establishes the face angle and three center-to-center offsets between those machined faces. The [water-pump housing joint guide](/cars/1975-mg-midget/water-pump-housing/) provides a source-backed gasket diagram, bolt checklist and measurement plan. The oblique drawing’s left/right orientation, head seats, engaged lengths, washer dimensions and this car’s fitted hardware remain unverified; the virtual head is not a measured drilling or tightening guide. The same catalogue lists three pump-to-housing studs and nuts at the other gasket joint. A [replacement GWP128 pump photograph](https://classiccarparts.co.nz/water-pump-triumph-herald-13-60-spitfire-mk4-1500cc-1500-mg-midget-1500-with-gasket-gwp128) provides an additional silhouette comparison, without verifying fit on this car. [Moss's early 1975 thermostat-housing listing](https://mossmotors.com/363-370-thermostat-housing) warns of a cooling-system warranty modification that changed housing, tank and hoses for some cars. The exterior housing shape, outlet angles, bolt centers and relative offsets remain provisional; the pulley, belt, clutch and fan axial positions are not owner measurements. Identify chassis number, fitted casting and hose layout before a cooling repair or parts order.

A directly measured lower-hose metal-neck outside diameter (20–55 mm) and exposed shoulder-to-lip projection (15–90 mm) now resize that neck in a separate owner STEP build. The provisional casting shoulder stays fixed; the lip moves with measured projection. Measured port spacing, pump-seat offsets and bolt lengths stay in the owner export under `recorded_but_not_applied_mm`; the smaller joint-face angle stays under `recorded_but_not_applied_degrees`. Neither changes the STEP until the complete 3D relationship between the machined faces and their hole patterns is established. The neck bore, bead, shoulder location, hose clearance and fitted housing variant remain unverified.

**Unresolved housing geometry:** The public STEP currently assumes the engine-side 138702 and pump-side 138701 gasket planes are parallel. A [used 144297 casting view](https://rimmerbros.com/Item--i-144297U) and [multiple 144297A replacement views](https://www.ebay.co.uk/itm/267082515780) show separate mounting interfaces but do not establish the angle between their machined planes. The assembled owner's fitted casting is not identified, and oblique photographs cannot determine a trustworthy face angle or center offset. The present pattern placement is wrong because a trial housing bolt crosses the virtual pump. Parallelism itself is unverified. The virtual casting therefore cannot validate housing-to-head bolt access, joint spacing or a pump-removal path. The recorded angle and offset fields must remain observations until measured faces can drive a rebuilt casting and clearance checks.

The [Midget 1500 external-engine parts plate, PDF p. 32](https://mossmotors.com/media/wysiwyg/catalogpdf/spm_catalog_web.pdf#page=32) identifies the front engine plate, timing-cover gasket and separate oil seal. A [photograph of a removed Spitfire 1500 timing cover](https://www.clubtriumph.co.uk/forums/topic/20429-removing-timing-cover-spitfire-1500/) supports the long pressed-oval shell, flange and seal near one end. A supplier lists the [UKC1110 seal](https://classiccarparts.co.nz/triumph-timing-cover-oil-seal-front-crank-shaft-oil-seal.-ukc1110) for the Midget and Spitfire 1500 at **76 mm outside diameter, 52 mm inside diameter and 10 mm thickness**. This comparison size now scales the separate CAD seal, cover opening and crank-pulley hub. Using the seal diameter against the nearly face-on removed-cover photo suggests a roughly **216 × 336 mm** oval envelope; this is a photo estimate, not a factory cover drawing. The fitted seal and cover have not been identified on this car. Front offsets, bolt pattern, seal lip and fit remain estimates; the model does not supply a gasket pattern or seal installation dimension.

The cover's long axis follows the model crank-to-cam line. The prior upright oval intersected the upper cam sprocket and chain; a Boolean check of the revised cover finds no overlap with the chain, either sprocket, front plate or front seal. The newly traced housing rear flange and upper passage likewise clear them. The water-pump center is now y=30 mm, near the photo-scaled housing gasket center at y=40 mm. At its old y=−24 mm station, the seat crossed the chain and cover and the pump body crossed the cover. A Boolean check at the new station gives zero solid overlap for those three pairs. The new station is inferred from gasket relationship and geometric clearance, **not measured on this car**. It does not establish the casting's actual position, rear-to-front depth or a removal path; measure those before using the model for timing-cover or pump access planning.

A [supplier photo of the UKC774 viscous-style pump](https://www.jamespaddock.co.uk/water-pump-viscous-type-late-1500-models-4) shows an impeller behind the three-hole flange, a narrowed bearing section, a deep grooved sheave and a splined forward nose. The pump model now exposes those features instead of a single cone and solid disk; the sheave remains a separate selectable CAD part even though the photographed candidate is an assembled pump. The virtual pump and sheave no longer have a solid overlap. Their axial dimensions and tooth/groove profiles are still estimates, and UKC774 has **not** been identified on the owner's car. The modeled fan and clutch stations were moved forward to follow the longer pump nose; radiator clearance has not been measured.

The [Rimmer 1500 pump assembly listing](https://rimmerbros.com/Item--i-GRID005566) specifies three 5/16 UNF × 1¼ in studs, with separate viscous (100433) and non-viscous (TE605105) numbers; its [GHF201 listing](https://rimmerbros.com/Item--i-GHF201) confirms three matching plain nuts for the Midget 1500. The STEP now exposes all six pieces separately at the photo-derived 138701 gasket centers. Their nominal stud diameter and length are catalog based. The stud engagement, nut hex size, actual bolt centers, washer arrangement, access and tightening specification are not yet measured, so these shapes help locate the hardware but cannot prove wrench access or supply a torque value.

The [Moss 1500 cooling list](https://mossmotors.com/media/wysiwyg/catalogpdf/spm_catalog_web.pdf#page=37) and its [Smiths gauge instructions](https://mossmotors.com/media/instructions/361-761.pdf) distinguish the capillary temperature-gauge adaptor used through 1977 from the later electrical sender listed from chassis 200001. IMG_6895 shows a spiral-protected narrow line at a hex fitting beside the lower hose, consistent with a capillary connection. The STEP now separates a comparison 11K2846 adaptor, AED172 copper washer and short capillary bulb/nut end. A [Rimmer adaptor photo](https://rimmerbros.com/Item--i-11K2846) informs its visible shape. The fitted adaptor, boss assignment, nominal thread, washer size, bulb length and line route to the dash are still unverified; the geometry must not be used to order a sender or assess withdrawal clearance.

The [Rimmer 144297A replacement-casting photograph](https://rimmerbros.com/Item--i-144297A) reveals the lower-radiator-hose spigot and two tapped bosses absent from the previous housing model. Those features are now part of the STEP. A roughly 34 mm spigot outside diameter and 47 mm exposed projection are proportions estimated against the pictured pump opening, itself tied only approximately to the 138701 gasket photo. The owner’s IMG_6895 confirms a lower hose, clamp and wired fitting near this housing, but does not establish the full casting, either thread, or the radiator-end hose route. The modeled neck station is constrained to clear the pump, timing cover and block; it is not a direct owner-car measurement.

The [factory Midget 1500 cooling parts plate](https://www.spridgets.de/downloads/Parts-1977.pdf#page=64) lists GTG103 at the thermostat-outlet joint, CHA440 at 5/16 UNF × 1¼ in, CHA441 at 5/16 UNF × 1 in, and two WL208 lock washers. A [GTG103 ruler photograph](https://classiccarpartsaustralia.com.au/gasket-triumph-thermostat-housing-gtg103-115467) suggests an approximately 49 mm opening, 70.5 mm bolt spacing and 87 × 58 mm outside envelope. The STEP now separates the two-ear flange, gasket, and two catalog-length screws. The gasket dimensions and screw-hole assignments are provisional photo interpretations, and the factory plate distinguishes different 1975 North American outlet variants. The actual installed casting, face angle, screw positions, tool clearances and thermostat seat are not measured; this joint remains an identification aid, not a fitment model.

The first fastener fit check exposed a false collision between the top pump stud and the modeled thermostat outlet. IMG_6895 places the real outlet casting above the pump and pulley. Moving the provisional thermostat station upward and extending the modeled upper coolant passage now gives zero solid overlap for stud–thermostat, nut–thermostat, housing–timing-cover and housing–chain pairs. This establishes an internally coherent **study layout**, not the car's exact outlet height or a validated hose path. Measure the real centers and front-to-back projection before planning a pump removal around it.

A later Boolean audit exposed additional false volumes in the study: approximately **6,182 mm³** where the water-pump housing filled the pump, **7,071 mm³** where the alternator case entered the block, and **2,267 mm³** where the thermostat housing entered the pump housing. The pump impeller moved 1 mm forward, an inferred cavity was cut in the upper pump passage, the alternator and its pulley/fan pivot moved 14 mm outboard, and the thermostat and filler assembly moved 9 mm upward. The lower alternator bracket now stops at the block surface, and its adjusting link moved ahead of the block face. Rechecked pump–housing, alternator–block, bracket–block, link–block and housing–thermostat volumes are zero. The link still meets the timing-cover envelope with a small modeled overlap; its actual fixing plane has not been established. These edits remove contradictory study geometry, **not** establish factory mounting coordinates or service clearances. Verify the fitted castings and bracket centers before using any of these interfaces to plan a replacement.

The same [external-engine plate, PDF p. 32](https://mossmotors.com/media/wysiwyg/catalogpdf/spm_catalog_web.pdf#page=32) identifies the spin-on oil filter (item 52), separate filter-to-head adapter (53), head-to-block seal (54), and head bolt (55). **IMG_6966 clearly reads ACDelco PF53** on the canister fitted to this car. The [PF53 product listing](https://www.jegs.com/i/acdelco-065-pf53-engine-oil-filter-spin-on-canister) gives about **77.0 mm outside diameter, 79.4 mm height, ¾-16 thread, and 70.4/62.2 mm gasket outside/inside diameters**. Those catalog dimensions now control the separate canister and gasket study instead of the former 76 × 100 mm MANN comparison; they are not direct measurements of the installed filter. The CAD also separates the mounting head, adapter and block-side seal. [Rimmer lists GFE119/GFE150 for the Midget 1500](https://rimmerbros.com/Item--i-GFE119) but warns that aftermarket adapters can have different threads. The [GFE150 listing](https://bpnorthwest.com/mg/oil-filter-5-8-opening-spitfire-see-note-midget-1500/) has a ⅝-inch opening, and the [MANN W 713/14 comparison](https://www.mann-filter.com/ca-en/catalog/search-results/product.html/w713/14_mann-filter.html) specifies ⅝-18, unlike PF53's ¾-16. A [⅝-18 to ¾-16 conversion stud](https://www.olphartz.com/store/p861/Oil_Filter_to_Block_Adapter.html) is sold for these cars, but its presence here is unverified. **The actual adapter thread, seal seat, head profile, passages, bolt and removal clearance are still unknown.** Use the [PF53 fitment study](../oil-filter/) before choosing a replacement; the CAD is not an oil-routing or machining drawing.

The crank, water-pump and alternator pulleys are **separate selectable STEP and browser parts**. A [TKC1425 supplier listing for 1974–79 USA/Canada Midget 1500](https://www.scparts.co.uk/en/pulley/201543/) specifies a **148 mm outside diameter and two-belt crank pulley**. The earlier CAD sheave was only 74 mm across; the reconstruction now uses the catalog outside diameter, shows two V grooves with an estimated smaller forward groove and a recessed front, and routes the displayed belt around a contact circle inside that rim. The fitted crank pulley is not visible clearly enough in the owner photographs to confirm TKC1425. Its groove profile and spacing, hub, projection, belt lane and secondary-belt equipment remain provisional. The belt loop uses the factory belt topology and IMG_6859 as visual references. The pale virtual fan has **13 blades**, matching the [North American 1500 catalog listing](https://rimmerbros.com/ItemList--MG-Midget-1500-Fan-Viscous--m-24677) (Moss 434-570, Rimmer RKC92); the earlier four-blade study was wrong. [MGOC also lists a seven-blade 1500 fan](https://www.mgocspares.co.uk/parts/mg/midget/cooling/water-pump-fan-thermostat/1500cc), but the [Spitfire catalog plate](https://rimmerbros.com/Images/PDFs/Spitfire.pdf#page=20) associates RKC2126 with the non-viscous arrangement and RKC92 with the viscous arrangement. The seven-blade listing is a configuration comparison, not a confirmed drop-in replacement for the modeled viscous coupling. The owner's photos do not show all blades or the mount for a reliable identification. A separate viscous-coupling envelope follows the catalog assembly plate. Blade shape, fan diameter and clutch dimensions remain placeholders.

Selecting a front-drive part opens an eight-stage **water-pump assembly study**. It moves the belt, fan and clutch, water-pump sheave, three nuts, pump and gasket in sequence, then returns them to their seats. With the optional radiator shown, the straight-ahead fan/clutch animation stops 2 mm before the displayed core face instead of passing through it; if the direct core-face gap is unavailable, that stop uses the placeholder gap and proves nothing about actual access. Later exploded offsets expose relationships and may overlap other parts. The sheave is separated for inspection in CAD even though the UKC774 candidate photograph shows it assembled with the pump. These motions are **not** a factory removal sequence or verified withdrawal path. The real fan-to-radiator gap, hose path, pulley construction and fitted pump variant must be checked before planning a repair.

The optional radiator comparison gives the front-drive view a body-fixed obstruction. [Moss's 1975 cooling plate](https://mossmotors.com/media/wysiwyg/catalogpdf/spm_catalog_web.pdf#page=37) identifies the early crossflow radiator as 459-740, to chassis 166303. A [replacement 1500 radiator listing](https://gpiracing.com/products/for-mg-midget-1500-mt-1974-1980-1979-1978-1976-1975-aluminum-radiator) gives a **422 × 258 × 40 mm core**; those dimensions scale the optional CAD core. IMG_6859 shows side tanks and the close fan relationship, but cannot supply the installed tank dimensions or front-to-back station. The public STEP radiator is therefore a provisional comparison envelope at a placeholder station. The browser hides it by default. Directly measured core width, height and thickness resize its browser preview; the visual side tanks retain their estimated dimensions as the core changes. A **direct fan-tip-to-core-face gap** in the water-pump worksheet moves the browser envelope to that datum; a separate owner STEP build can also use the gap and core dimensions. The older field allowed either the core or shroud and remains in the log only; it cannot position the core. The displayed gap does not establish a safe withdrawal path. The fitted radiator identity, cowl, mount, hose necks and minimum blade clearance remain unverified.

The pump study has a car-specific access worksheet in the CAD inspector. It records the fan-to-radiator gap, the distance from the pump flange front face to the first fixed obstruction in the intended dismantling state, the **front projection of the pump nose from that same face**, the longest exposed stud tip, pump-flange thickness and impeller depth behind the rear flange face. The pump nose matters: the old worksheet compared the whole flange-to-obstruction distance against withdrawal distance even though the nose already occupies part of it. With direct measurements, the corrected available travel is `flange-to-obstruction − pump-front projection`; the known straight-withdrawal lower bound is `max(stud projection + flange thickness, impeller rear projection)`. Existing saved entries retain their original flange-to-obstruction meaning and receive no clearance result until the new nose measurement is supplied. Less available travel than the known bound flags a conflict for a straight path with studs left in place. More space does **not** establish a usable removal route because radiator shape, hoses, tool sweep and angled movement are not modeled. Entries stay in browser storage and can be exported with the existing measurement log.

The belt reference also needed a variant check. [British Parts Northwest](https://bpnorthwest.com/mg/midget/fan-belt-mg-midget-1500/) cross-references Midget 1500 belt CHA328 to GCB11113 and Moss 434-590; [Rimmer lists a GFB11113 comparison at roughly 1113 mm × 10 mm](https://rimmerbros.com/Item--i-GFB11113). A [viscous-fan CHA328 seller](https://garage-maruichi.shop-pro.jp/?pid=144792533) describes about **1120 mm outside circumference**. That same seller identifies the previously cited [GCB11088, about 1088 mm outside, with a fixed-fan variant](https://garage-maruichi.shop-pro.jp/?pid=144792986), although some broad Midget 1500 listings do not distinguish the versions. Neither belt has been identified on this car. The generated CAD belt wraps sampled pulley circles at the modeled centers; in the current public build its outside perimeter is **989.9 mm**. The shortfall against the viscous-fan outside reference remains too large to use this loop to select a belt. The belt inspector accepts **three direct shaft-center distances** and calculates a separate triangle-based outside outline using the recorded direct pulley outside diameters where available. It does not move the public 3D stations or engine STEP; the separate owner front-drive STEP above moves its isolated pulley centers. However, groove contact radii, occupied lane, belt datum and fitted belt marking still need direct inspection before choosing a replacement. Each component remains a separate STEP part so measured replacements can be substituted independently.

The formerly independent virtual groove centers were about **217 mm at the large crank groove, 215.5 mm at the pump sheave and 211 mm at the alternator pulley** on the model's Z axis. A six-millimeter spread made the virtual belt internally inconsistent. Their centers and the browser belt preview now share a single **215.5 mm provisional lane** set from the prior pump sheave station. This enforces a straight virtual belt; it does not establish the car's fitted pulley alignment. The web belt remains a route cue and can intersect the provisional pulley material. The belt inspector records the absolute pump and alternator groove-plane offsets from the occupied crank groove; record which direction each lies in the source note. A straightedge check on the fitted grooves and direct axial datums are needed before the model can judge belt alignment.

Fan references: Moss Midget 1500 cooling plate, item 55 fan and item 56 clutch (<https://mossmotors.com/media/wysiwyg/catalogpdf/spm_catalog_web.pdf#page=37>); Rimmer's North American Midget 1500 listing names the 13-blade RKC92 fan (<https://rimmerbros.com/ItemList--MG-Midget-1500-Fan-Viscous--m-24677>). IMG_6895 shows irregular missing material at several fan tips, with IMG_6850 and IMG_6854 providing earlier context. Their condition and the installed part number need direct inspection before repair or redesign.

The 13-blade study silhouette uses a broad swept planform after comparison with [Rimmer's RKC92 product photograph](https://rimmerbros.com/Item--i-RKC92) and a [British Parts Northwest front view](https://bpnorthwest.com/mg/fan-blade-spitfire-75-to-78-midget-75-to-79/). Its blades now sweep tangentially through six radial sections with a provisional 14–31° pitch progression, informed by the side view in IMG_6895. The catalog photo also informs a smaller rounded-square center opening and four lightening windows; those cutouts remain visual estimates, not a measured mold pattern. The roughly 35 mm tip chord and section angles are visual reconstruction choices, not catalog dimensions or proof that RKC92 is on this car. The model retains complete blade tips so possible damage in IMG_6895 is not mistaken for normal part geometry.

The fan mounting radius is an independent provisional parameter. Resizing the blades from a direct owner diameter does not move the fixing holes. An owner build accepts a directly measured 240–340 mm intact fan diameter and four signed X/Y mounting-hole centers, each recorded from the shaft center in a front-facing view. One 50–75 mm adjacent mounting-hole spacing is retained as a comparison note but cannot move the pattern. If it is recorded with all four centers, the owner builder checks that it agrees with a neighboring pair within 3 mm; an inconsistent set is rejected. The full set of hole centers changes the shared fan, clutch and four fixing stacks; it does not identify the fan variant or validate hole size. The owner build solves for the radial parameter that makes the provisional blade silhouette's actual X envelope match the recorded X diameter; its Y extent can differ because this is a swept, 13-blade shape. A directly counted 4–16 blades can change repetition in a separate owner build, but it reuses the candidate RKC92-style paddle; count alone does not establish the fitted blade profile, pitch or variant. The public model stays at its provisional sizes until direct measurements are supplied.

[Rimmer's UKC3532 clutch photograph](https://rimmerbros.com/Item--i-UKC3532) shows a finned disc with four fixing holes outside its central seat. The earlier narrow CAD cylinder could not meet the fan's four-hole spider. This revision uses a provisional 120 mm disc and aligns four clear holes through the fan and coupling. Four separately selectable GHF102 bolts use the [catalog 1/4 UNF × 1½ in length](https://rimmerbros.com/ItemList--MG-Midget-1500-Fan-Viscous--m-24677); GHF200 nuts and GHF300 washers are separate selectable groups. Their sides, head profiles, spacing, hole sizes, clutch depth, fin geometry and installed fit still require confirmation on this car. The fit audit checks that the fan, clutch, bolts and nuts do not occupy each other's nominal clearance holes.

Before trying to model the actual car faithfully, confirm its engine prefix (factory Midget: FP; Spitfire: FM), then measure or scan the block, head, sump, manifolds, carburetor, engine mounts, and fitted emissions equipment. The manufacturer part catalog is useful for identifying model-year and market variations; a match in the shared engine family alone is insufficient to establish part fitment.

The [factory 1500 engine-mount plate, PDF p. 72](https://www.spridgets.de/downloads/Parts-1977.pdf#page=72) identifies handed front brackets CHA257/CHA258, two early front rubbers CHA280 replaced in the list by CHA565 from GAN6-166304, two rear rubbers 122689 replaced by CHA615 from GAN6-176236, and a North American restraint assembly. The owner's GAN6 chassis number and fitted mount geometry are still unknown. These supports are intentionally absent from the engine STEP until their exact variants and engine/body mounting coordinates are recorded; the [engine-mount guide](../engine-mounts/) collects the source and the required measurements.

This file is suitable for an interactive visualization and for continuing the reconstruction. It is **not** a machining, inspection, or repair drawing.

For assemblies with separately modeled retainers, the inspector's **Show modeled fasteners** control highlights those groups through surrounding surfaces and offers a direct link to inspect each group. It covers only the currently modeled hardware, such as the fan, cover, pump, alternator and clutch fixings. A highlighted location is an aid to finding a part on the car; the virtual stations and tool access are not validated unless a specific source or direct measurement says otherwise.

The **Check CAD distance** control now lets a desktop or touch user choose two visible mesh surfaces. The viewer draws two markers and reports the straight-line distance and side, height and front/back components in millimeters. Starting the tool returns the exploded and guided-study positions to assembled state; changing the explode slider clears the previous points. A third tap starts a new comparison. These are distances in the **displayed reconstruction**, not measurements of the actual car. In particular, the current block, head, manifolds, mounts and many fastener positions have provisional geometry, and mesh tessellation limits surface precision. Record direct dimensions on the car before using a displayed gap for removal clearance or parts fit.

## Second owner-photo set and fidelity targets

IMG_6885–6903 are browser copies in `../../assets/photos/`, with the originals held in the owner's `mg midget 2` folder. The [photo archive](../photos/) and [locator](../locator/) identify the added evidence. IMG_6885–6887 reveal the separate metal air-cleaner case, elbow and two-clamp rubber coupling. IMG_6892 shows the SMITHS marking and hose/outlet arrangement on the heater. IMG_6893 shows a silver pressure-warning-stamped cap appearing over the cover; IMG_6856 shows a dark cap at the opening. Whether the silver cap was fitted or merely placed there is unresolved. IMG_6897–6898 show the installed blue ACDelco spin-on filter and a labeled electric fuel pump. IMG_6895 shows multiple irregular fan tips.

The public STEP and browser geometry now include separately selectable study groups for the photographed electric fuel pump: horizontal barrel and rolled ends, white and red label bands, curved retaining strap and visible mounting foot, end fittings and terminals, and the adjacent silver line canister whose function is still unidentified. The label bands are surface cues, not service parts, and do not reproduce the unreadable lettering. This is a **body-mounted accessory**, not part of the original engine casting. IMG_6898 is the sole geometry reference; the nominal 70 mm barrel diameter and 100 mm barrel length are perspective-sensitive estimates, and the relative position near the oil filter is illustrative. No maker, model, pressure, flow direction, wiring polarity or connection size is inferred from the photograph. The CAD inspector records direct barrel diameter, barrel length and pump-to-filter spacing. Exported direct diameter and length can resize the barrel and strap in a separate owner STEP build; the connection sizes and body station remain provisional. These entries do not reshape the public STEP.

The new STEP parts preserve these *observed component relationships*, but the case sizes, duct diameters, filter size, cap geometry, hose ports and installation coordinates are still **provisional**. Photos taken at an angle cannot by themselves deliver machining-grade or 1:1 exterior surfaces. To replace each provisional shape, photograph perpendicular views with a ruler in the part's plane, measure all three outside dimensions and center-to-center mounts directly, and record the installed number. The CAD inspector now lists the exact next measurements for these parts. Do not use the provisional STEP surfaces for repair fitment.

## Owner measurements in the browser

The CAD inspector now shows the selected group’s X/Y/Z bounding envelope and lets the owner record corresponding dimensions measured on this car. X runs side to side, Y is vertical and Z follows the crankshaft. Entries are saved in browser storage and can be exported as a JSON measurement log with the current model envelope, evidence type (direct measurement, photo estimate or reference), measurement point/source and date. These measurements do not silently reshape the STEP: each recorded difference is a prompt to revise the parametric source, regenerate the assembly and validate it against another independent dimension or photo. This preserves a clear distinction between a car measurement and a provisional model size.

The rocker-cover inspector also records stud center spacing, the cap seat diameter, the minimum gap to the latched bonnet, and the unobstructed vertical lift with the bonnet open. The CAD fastener spacing is currently **152 mm provisional** from `build_engine.py`; it is not a specification or a measurement of this car. These four features make the first virtual replacement study testable against the installed assembly. A saved value includes the same evidence method and source note as the envelope values. The garage planner's backup includes these CAD measurements for transfer to another device.

Directly measured **three adjacent bore-center intervals** and independently measured **deck and lower-block casting widths**, cover X/Y/Z and stud-center spacing, **direct X outside diameters of the crank, water-pump and alternator pulleys**, the **directly counted fan blades, intact fan outside diameter, blade-tip chord and four signed fixing-hole centers**, radiator **core width, height and thickness**, the **fan-tip-to-core-face gap**, and directly measured **alternator case diameters, four axial case-section lengths, both lower-ear thicknesses and inside-ear gap** can produce a **separate owner-measured STEP and web-geometry build**. Select a part in the CAD inspector, open Measurements and model details, enter direct values with a measurement-point note, choose “Measured directly on this car,” save, and export the log. The block needs all three bore-center fields to move bores, while either named width can resize its own block section independently. A single bore interval does not force an equal-pitch assumption onto the other two. For the radiator use the named *core* fields, not the whole-part X/Y/Z envelope; for its station use the *core-face* gap under Water pump. Install CadQuery, then run `python build_engine.py --measurements /path/to/midget-1500-cad-measurements.json --output-dir /path/to/output`. The script accepts any supported direct subset, rejects photo estimates and reference-only entries for geometry, checks numerical ranges, and writes `measurement-provenance.json` beside the resulting geometry. It does not overwrite the public study. A directly counted number of fan blades changes repetition using the candidate paddle profile; the measured fan diameter changes blade span; a direct intact-blade tip chord changes paddle width; four directly measured hole centers change the shared fan, clutch and fixing pattern. A single adjacent spacing is recorded but does not alter geometry. Without a direct count, its blade count remains unverified; pitch, root contour, hole bores and installed variant remain unverified even after a count is recorded. Pulley diameters and a direct alternator shaft-to-pivot distance regenerate the belt outline, but **absolute shaft stations, groove shape, belt lane and alignment stay provisional**, so a measured diameter alone cannot validate belt fit. Radiator tanks, cowl, mounts and hoses, as well as block and cover topology, fastener thickness, gasket, cap and removal clearances, remain provisional. Do not publish a measured build as a fitment model without inspecting those interfaces.

The CAD page can now open the web JSON from a separate owner build directly from a local file. Run the command above, then use **Open a measured CAD build** below the model and choose the generated `midget-1500-measured-core.json`; the file is read in the browser and is not uploaded. Current owner builds embed the same measurement provenance that is written separately to `measurement-provenance.json`. The badge identifies the local build and the inspector shows its geometry. Reload the page to restore the public model; the public STEP download is labeled as different while a local build is open. Browser-only size previews are disabled for imported geometry to prevent applying measurements twice. The matching owner STEP remains in the selected output directory. Geometry that was never measured remains provisional.

For a garage inspection, select any CAD part and choose **Print a field sheet for this part**. The sheet brings together its owner photo, function, fasteners, access warning, current model envelope, named measurement prompts, saved browser observations and further evidence tasks. Blank lines leave room for direct measurements and notes; it can also be saved as a PDF. The model envelope is labeled as reconstruction geometry, not a specification of the fitted car. The alternator front, stator and rear-cover groups now point to the marked IMG_6972 case view; pivot groups point to the IMG_6971 lower-mount view. Neither photograph establishes hidden bolt identity or a removal path.

The owner build now applies eight independent alternator-case measurements: four outside diameters—front silver casting **112–140 mm**, dark stator band **100–132 mm**, rear silver casting **110–140 mm**, and dark rear shroud **95–130 mm**—and four axial lengths—front silver casting **20–70 mm**, dark stator band **10–55 mm**, rear silver casting **15–75 mm**, and dark rear shroud **10–70 mm**. The front face, fan and pulley lane stay at the original comparison station; each measured section moves the seams behind it. The provisional rear connector silhouette follows the shroud's rear surface. A provisional web joins the rear ear to the shroud; its contour is not a Bosch measurement. The provisional web extends to the shroud when direct section measurements move it away from the unmeasured rear-ear station. This is section-envelope reconstruction, not a measured AL298X casting, stator, or electrical connector. Direct front and rear lower-ear thicknesses (5–14 mm each) and the inside-ear gap (70–98 mm) can now change the separate owner STEP: the rear ear and spacer follow the gap, and the retainer follows the front ear. The public 12 mm bracket lug determines its 73 mm comparison spacer length. A separate owner build now accepts a directly measured lug thickness (7–22 mm), spacer length (48–90 mm), outside diameter (12–26 mm), and bore diameter (8–11 mm). It also accepts directly recorded total washer/shim-pack thicknesses at three internal positions: rear ear to spacer (0–10 mm), spacer to lug (0–10 mm), and lug to front ear (0–4 mm). The owner STEP places one provisional annular envelope per positive pack; its individual pieces, bores and outside diameters remain unmeasured. The builder checks that spacer, lug and packs together fill the measured clear ear gap within 0.5 mm. Record the count and order in the source note, and recheck a mismatch rather than forcing it into the model. The browser inspector reports this axial sum once G, S, L, R, M and F are all saved as direct observations; enter zero only for an inspected empty pack. The builder rejects measured lower-mount stacks that exceed the selected bolt length, which defaults to the provisional 127 mm catalog comparison. A directly measured 75–115 mm shaft-to-pivot distance now moves the alternator case, rear housing, shaft, fan, pulley and comparison belt outline around the fixed provisional lower pivot. The front lower web stretches to keep the ear connected; its outline is still an estimate. Absolute alternator engine placement, the upper adjusting-link fit, front-ear axial station, bracket position and width, unmeasured spacer features, connector projection and bolt access remain unverified. The public STEP uses provisional 124 / 114 / 120 / 110 mm outside diameters and 34 / 25 / 40 / 30 mm axial sections.

The wider axial ranges were checked with a synthetic 60 mm front-casting entry, not a measurement from this car. That owner STEP exports and `verify_fit.py --measurements` reports no new non-mating overlaps. When a measured section moves the provisional rear ear beyond the dark shroud, its unmeasured connector web routes outside the silver case; neither that web nor the fixed ear station is fitment evidence.

For immediate visual planning, the browser inspector offers **Preview my pulley sizes** after a direct pulley diameter is saved. It rescales the three displayed pulley envelopes from their original shaft centers and redraws the belt loop around their resulting contact circles. The preview stays local to that browser and can be turned off with **Show catalog model**; it does not alter the public STEP, exported CAD JSON, other parts, groove profiles, shaft centers or belt alignment. The preview badge and belt note identify its approximate outside outline so it cannot be mistaken for a validated fitment drawing.

The fan inspector also offers **Preview my fan size** after a directly measured intact-tip diameter is saved in X. The browser rescales the outer fan region around a fixed 55 mm central mounting zone so the visible tip envelope matches the recorded diameter; **Show catalog fan** restores the published mesh. This immediate preview is approximate and stays in local browser memory. It does not reshape the four-hole fixing pattern, identify a damaged blade, verify the pitch or airfoil, measure the fan-to-radiator clearance, or change the downloadable STEP. An exported direct measurement can still drive a separate owner STEP build through the parametric source.

The [fitted-cover identification guide](../rocker-cover/) now records a separate fitment question. The Moss Midget 1500 cylinder-head plate lists two 4⅛-inch studs through 1976, versus two 3⁵⁄₁₆-inch studs from 1977 with different nuts, washers and O-rings; the perimeter gasket is listed separately for both. Those lengths are catalog part descriptions, not measured projection above the cover, so the current CAD fasteners remain provisional. MGOC Spares distinguishes early conventional-stud/cork-gasket and later O-ring/tube-nut 1500 rocker-cover arrangements, and Rimmer notes different stud requirements for a late engine receiving an alloy cover. The photographed red cover and cap do not establish the hidden gasket or stud variant. The CAD study therefore cannot be used to choose gasket or fastener parts until the owner's engine number and fitted sealing hardware are inspected.

IMG_6972 shows broad raised lands on both silver alternator castings. The default STEP now uses wider rounded lands so the casing silhouette is closer to that fitted unit from the observed side. Their number around the unseen circumference, angular positions, widths and projection are inferred. No case fastener, electrical terminal or removal clearance is located by these surfaces.

A [1979 Midget 1500 owner's engine-out photographs](https://arkymidget79.blogspot.com/2010/11/engine-progress-110910.html) show an upper alternator bracket attached at the water-pump housing. This is firsthand comparison evidence for the engine family, but does not establish the anchor or exact bracket on this 1975 car. The virtual link's engine-side tab currently floats clear of the modeled housing; the worksheet now asks which casting or bracket actually carries that tab. Its timing-cover-face field is an axial datum, not an assertion that the tab bolts to the cover. No adjustment of the link or mounting holes should be inferred from the 1979 photo alone.

IMG_6964 provides an overhead owner view of a rusty plate with a large opening and nearby fasteners beside the rocker cover. It is a useful visual target for identifying the upper-link attachment but does not show the full slotted arm, bend, or casting beneath the small fixing. A [used-parts listing for CHA304](https://robertpieces.com/en/used-parts-for-british-cars/1919/alternator-bracket-mg-midget-1500-detail) has a product photograph whose tag appears to read CHA204. Because the catalog name and photographed tag conflict, that photograph is not a reliable footprint for the missing North American bracket. Obtain square-on fitted photos with a ruler and visible engine mounting bolts before adding CHA304 geometry or using the lower mount for removal planning.

The [factory Midget 1500 parts list, PDF p. 183](https://www.spridgets.de/downloads/Parts-1977.pdf#page=183) names HU858 for the link-to-alternator screw; a [replacement HU858 listing](https://www.ldpart.co.uk/shop/shop.php?c=viewproduct&cat=85&maincat=1&pid=246) describes a nominal 5/16-inch UNC × 1-inch set screw. In the former CAD, the upper-ear hole projected 16.5 mm short of the slot's nearest end-center, and a projected 7.9375 mm shank intersected about 198 mm³ of solid link. The 7 mm slot was also narrower than that nominal shank. The comparison slot now measures 44 × 9 mm, with its near end centered over the modeled ear hole; a projected shank at the current link plane intersects zero link material. This fixes one internal topology error without verifying the fitted screw or slot. The 20 mm axial gap, engine-side attachment, and timing-cover overlap remain unresolved; the slot cannot be used to infer a bolt length, washer stack or adjustment range on the actual car. `verify_fit.py` now checks this projected bolt aperture separately.

The [Rimmer 156464 product photograph](https://rimmerbros.com/Item--i-156464) and a [second supplier view](https://www.jamespaddock.co.uk/alternator-adjusting-bracket-8) show radiused stamped corners at both ends of the link. The STEP now rounds the provisional tab and slotted-arm perimeter by 3 mm so those edges read like the photographed part. This radius is a display estimate; the photos are oblique or low resolution and do not establish a manufacturing profile, tab-to-eye spacing, bend station, fitted link variant or the attachment point on this car.

The [factory Spitfire 1500 alternator-mounting plate](https://waghornswood.net.nz/Manuals_01_18/Vehicles/Triumph/Spitfire/triumph_spitfire_1500_1975_onwards_parts_catalogue.pdf) lists metric SH108251 with NT108041 and imperial HU858 with JN2158 as non-interchangeable upper-link fixing pairs around the shared 156464 link. The Midget parts book names HU858, but the photographed car carries a Bosch replacement alternator, so its fitted upper screw and mating thread must be checked directly. The inspector saves a directly verified metric, imperial, other or unidentified thread family in its exported log. If the log also includes a supported direct dimension, a separate owner build retains that observation in its evidence report without changing the comparison thread geometry. A wrench size or catalogue application alone is not a pitch measurement.

IMG_6967 shows the fitted distributor cap with four plug-lead positions and a central coil-feed position. The earlier STEP omitted the center tower despite the [distributor identification guide](../distributor/) asking the owner to record all five leads. The cap now exports five separate tapered, shallow-open terminal towers. Their diameters, heights, mouth depths and exact clocking remain visual estimates; only the four plug-lead routes are modeled, and none is a verified reconnection guide. Photograph and label the center coil lead as well as all four plug leads before disturbing the cap.

IMG_6973 shows a black ignition coil beside the distributor, marked “12V” and “USE ONLY EXTERNAL RESISTOR.” The [1977 North American factory parts list, PDF p. 175](https://www.spridgets.de/downloads/Parts-1977.pdf#page=175) names GCL111 as its ballast-coil catalog part and lists two bracket screws, but the fitted maker, part number, bracket and wire identities are not readable. A [Lucas DLB102 comparison listing](https://www.holden.co.uk/p/lucas_12_volt_coil_for_use_with_ballast_resistor) supplies the CAD's provisional 50 mm can diameter and 105 mm body length; it does not identify the fitted part. The model now separates the can, terminal end, strap, two fastener cues and an illustrative center lead. Selecting a coil part shows that group with the distributor, and the inspector can highlight the modeled strap and screw cues; this establishes component relationships, not a removal sequence. Their stations, shapes and lead route are visual guesses; the direct-measurement workflow can replace the can diameter and length only. See the [fitted-coil study](../ignition-coil/) before selecting a replacement or using the virtual assembly to plan access.

## First virtual replacement study

Selecting the rocker cover, its gasket, hold-downs or oil cap opens a five-stage virtual study: assembled reference, fasteners lifted, cover/cap lifted, gasket and rocker gear exposed, and reassembly. It is tied to the cold valve-clearance procedure and factory rocker-shaft drawing. The model groups and lift distances illustrate component order and access; they are **not measured motion paths**. A valid 1:1 rehearsal needs direct bonnet, lead, hose and fastener-clearance measurements on this car, followed by a check of the factory removal and reassembly procedure.

Selecting any of the four spark plugs now opens a four-stage ignition study: trace and photograph its lead, expose the plug, show an illustrative straight withdrawal from the provisional head bore, then compare and refit. The canvas shows the selected plug, its now-individual boot, its lead, the distributor and a translucent head. The boot moves aside and the lead hides at the disconnect step; the plug moves outward at the withdrawal step. The owner photos show lead routes but do not resolve the plug-end boots. The plug station, angle, head thread, boot grip and physical withdrawal clearance are unverified. Follow the linked factory-based workshop procedure and identify the plug actually fitted before choosing a replacement, socket or tightening method.

## Air-filter measurement handoff

The photo-led shape pass now uses rounded stamped-case sections. The factory plate establishes the **assembly order and opening side**, while IMG_6886 supports the curved outboard cover and two side latches. Corner radii, cover depth, seam position, sheet thickness and passage diameter are still modeling estimates. The full outside comparison envelope is 100 × 150 × 280 mm until measured directly.

The [factory North American plate](https://www.spridgets.de/downloads/Parts-1977.pdf#page=122) names one GFE1060 element for the 1975 catalog assembly. The [WIX manufacturer interchange, PDF p. 674](https://content21.blob.core.windows.net/web-hosting/clients/mann-hummel/estore/catalogs/2024/2024%20Wix%20Interchange%20and%20Product%20Numeric%20Catalog%20Web.pdf#page=674) maps GFE1060 to WIX 42151. Neither source measures the filter fitted to this car. A [TR8 cross-reference compilation](https://triumphwedgeowners.org/crossref/02_Data/FuelEmission.htm) quotes 29.7 × 28 × 4.8 cm, but its accompanying product photo shows a long, narrow element; that dimension claim is unsuitable for CAD scaling without an independent measurement.

The browser inspector labels filter X/Y/Z as **outboard-to-carb-side thickness, vertical height and end-to-end length including its seal or frame**. Earlier saved filter values used a different axis interpretation: the inspector warns about them, and `owner_measurements.py` requires the `vertical-panel-v2` marker from a fresh save before applying a direct filter measurement. A directly measured element can resize a separate owner STEP build only when the measured case provides clearance. Gasket compression, mounting and removal clearance remain unverified.

## Owner adjusting-link planes

The adjusting-link inspector can apply two direct axial measurements to a separate owner build: the gap from the upper alternator ear's front face to the slotted arm's rear face (0–45 mm), and the offset from the timing-cover crown's front face to the engine tab's rear face (−35 to +35 mm, positive toward the radiator). The builder moves those two planes and redraws the connecting bend; it rejects a bend exceeding 45 mm or a resulting intersection with the virtual front plate or timing cover. The reference planes at Z = 183 and 202 mm belong to the provisional public reconstruction, so these inputs do not establish the link's real engine station. A collision means the unmeasured XY path or tab anchor needs more evidence; it does not disprove the car measurement. Photograph both stacks side on and identify the actual tab anchor before using the drawing to plan access. The public link still has a 20 mm upper-ear gap and intersects the provisional cover. The link's XY outline, slot and bolt locations remain estimates.

A direct slot center-to-center travel of 10–100 mm changes the slot and length of the slotted arm in an owner STEP. A direct clear slot width of 5–12 mm changes its opening and the adjoining arm edge, retaining at least a 2 mm provisional outside web along the long arm. The virtual near slot end remains at the provisional upper-ear hole projection. Wider measured openings require the eye and surrounding web to be measured before this topology can be trusted. The tab, lifting eye and their relative positions are not determined by these two measurements. Eye-to-slot spacing, bend offset and observed anchor identity are retained in the owner-build evidence report without changing geometry. Compare the built shape with a square-on photo before treating it as the fitted link.

The [Moss Europe Midget catalogue, printed p. 183](https://www.moss-europe.co.uk/content/files/pdfs/moss-europe-sprite-midget-catalogue-issue-25.pdf#page=241) identifies 156464 as the adjusting link for 1500 FP engines and lists BH605181 as the link-to-thermostat-housing bolt with one lock washer. Its [cooling list, printed p. 137](https://www.moss-europe.co.uk/content/files/pdfs/moss-europe-sprite-midget-catalogue-issue-25.pdf#page=195) also assigns BH605181 to one of three housing-to-cylinder-head bolts (exploded-view item 16). This cross-index raises a possible shared fixing, but two catalog entries do not prove that one physical bolt serves both functions on this car. [Rimmer identifies BH605181](https://rimmerbros.com/Item--i-BH605181) as a 5/16 UNF × 2¼-inch hex-head bolt with a ½ AF spanner size. The public link tab center is about 84 mm away in XY from the photo-traced right/lower housing-gasket hole. That is an internal model discrepancy, not a measured gap on the car or an identification of item 16. The link geometry cannot be used to choose a removal route. [IMG_6889 with a marked fastener group](../locator/?view=alt-housing-bolts) provides a specific in-car inspection target; trace the actual link tab to its bolt before relocating either geometry in the CAD.


## Timing-cover hardware count

The [factory Midget 1500 parts plate B84, PDF p. 60](https://www.spridgets.de/downloads/Parts-1977.pdf#page=60) lists cover 217790, gasket 211126, five PT803 screws and five WL208 lock washers, six HU807 screws and seven WL208 lock washers, and one HN2008 nut. Thus it specifies 11 screws, one nut and 12 lock washers for the cover assembly. A [supplier photograph of replacement gasket 211126](https://bpnorthwest.com/mg/timing-cover-gasket-tr250-tr6-spitfire-gt6-mg-midget-1500/) shows 14 holes, matching the number of provisional holes in the virtual cover and gasket. The [Moss Europe 1500 parts catalogue, printed p. 127](https://www.moss-europe.co.uk/content/files/pdfs/moss-europe-sprite-midget-catalogue-issue-25.pdf#page=185), gives a clockwise A–P sequence viewed from the front: A and K are 5/16-inch dowels, C/D/E/F/J are five 5/16 UNF × 3/8-inch pan-head screws, B/G/H/L/M/N are six 5/16 UNF × 7/8-inch hex-head screws, and P is a 5/16 UNF × 1¼-inch stud with washer and nut. This reconciles the 14 holes with 12 threaded fixings. Moss uses later replacement codes and identifies 217790 as the multiple-timing-mark cover; the fitted car has not been inspected for this pattern. The STEP now separates two dowels, five short screws, six long screws and the stud/nut, including twelve washer silhouettes. Their shanks use the catalogue nominal 5/16-inch diameter and the cover/gasket/front-plate holes use 8.5 mm display clearance. The A–P mapping onto the fourteen photo-derived holes, head and washer envelopes, hole centers, depth of engagement and fitted hardware remain provisional. These are recognition cues, never a drilling or reassembly template. The [timing-drive field study](../timing-drive/#cover-hardware) has a position-group checklist for a real inspection.

A [photograph of a used cover identified as 217790U](https://rimmerbros.com/Item--i-217790U) shows a raised stamped collar around the front crank oil-seal opening. The former CAD had only a flat circular cut. The cover now has one integrated tapered annulus around its UKC1110 comparison seal: the bore follows the listed 76 mm seal outside diameter with 0.2 mm display clearance, while the 52-to-47 mm outside radius and 8 mm axial boss height (6 mm ahead of the provisional crown) are **visual estimates from an oblique photo**. The boss is one valid solid with the cover, and Boolean checks show zero overlap with the separate seal and pulley. Its actual draw depth, taper, seal interference, timing pointer and fitted variant remain unmeasured.

The cover inspector now accepts a direct outside diameter at the collar base (85–125 mm) and front projection from the adjacent cover face (2–20 mm). Those inputs change only the collar in a separate owner STEP; a directly measured base diameter preserves the photo-estimated 47/52 upper-to-lower radius ratio. The builder rejects a collar that overlaps the still-provisional pulley and explains which further axial station needs measuring. Record the two datum faces and the actual fitted cover identity before treating the owner build as a removal study.

## Crankshaft oil thrower 119390

The [Moss Europe Midget 1500 exploded drawing, printed p. 128](https://www.moss-europe.co.uk/content/files/pdfs/moss-europe-sprite-midget-catalogue-issue-25.pdf#page=186) identifies oil thrower 119390 as a separate piece in front of the crank sprocket and behind the pulley. A [photograph of supplied 119390](https://rimmerbros.com/Item--i-119390) shows a shallow dished plate with a notch at its center opening. The new CAD part uses that topology, an estimated 78 mm outside diameter, 35.4 mm comparison bore and 3.7 mm axial envelope. It is one valid solid and has zero calculated overlap with the public crank sprocket, timing cover and front seal. Its size, dish depth, axial station, key clearance and the actual fitted orientation remain unmeasured. Photograph it in place before a documented removal; the model is not a reassembly orientation instruction.

## Timing-chain tensioner mount

The [Midget 1500 catalogue, printed p. 128](https://www.moss-europe.co.uk/content/files/pdfs/moss-europe-sprite-midget-catalogue-issue-25.pdf#page=186) separates curved shoe 42425, anchor plate 43752, two RR610040 rivets, drilled pin 33214, two WP18 washers and two PS103121 split pins. A [42425 supplier photograph](https://rimmerbros.com/Item--i-42425) shows the curved spring strip and rolled eye that replace the former rectangular CAD shoe. A related [Triumph parts catalogue](https://www.moss-europe.co.uk/content/files/pdfs/moss-europe-tr5-6-catalogue-issue-23.pdf) describes the same 43752 plate as part of the timing cover, fixed with two RR610040 rivets. The STEP now separates the shoe, anchor, rivets and grouped pin hardware. Their shape and connection order are guided by the catalogue, but the strip bow, plate outline, rivet centers, pin stack and fitted positions are estimates. They are not an extraction path, rivet drilling template or chain-tension setting. Photograph the inside of the fitted cover and each retainer before disassembly.