Follow the motion
under the cover.
The timing chain links the crankshaft to the camshaft. The virtual engine now lets you select each gear, the 62-pitch chain, tensioner, cam retainer, lockplate and bolts. Use it to learn the assembly and prepare a record of what is fitted to your car.
The factory chain pitch and count and follower dimensions are firm manual data. Supplier photos appear to show 20 crank teeth and 40 cam teeth; those counts need a direct check on the fitted gears. The CAD’s approximately 149 mm cam-to-crank spacing comes from an ideal taut-chain calculation. The real tensioner, mounting coordinates, tooth form, fitted cover and timing phase have not been measured. A supplier-listed UKC1110 seal (76 × 52 × 10 mm) and removed Spitfire-cover photo scale the current oval, but do not identify this car’s cover or seal. The revised cover clears the virtual chain and gears, but the provisional water-pump housing still crosses the chain and cover; those meshes cannot establish removal clearance. Do not use the model to set valve timing or choose a replacement chain on its own.
What you can inspect in the model
Crankshaft gear
The matching 119389 single-row replacement lists a 35 mm shaft bore. The model now shows a separate gear, crank nose and keyway, but the actual key, shims and tooth profile still need checking.
Select crank gear ↗Camshaft gear
The 838-205 product photo shows four offset mounting holes and a single row of teeth. The model separates the gear, lockplate, two bolts and the cam retainer behind them.
Select cam gear ↗Chain and tensioner
Sixty-two roller stations follow the factory pitch around an ideal loop. The tensioner’s separate pivot and shoe show the assembly relationship; their positions and operating deflection remain illustrative.
Select tensioner ↗Followers and pushrods
Eight followers now use the factory 20.30–20.32 mm diameter and 44.45 mm length. Their bore locations, the pushrods’ lengths and the cam lobes still need direct evidence.
Select followers ↗Plan an inspection on the real car
- Identify the engine. Record its number and any visible replacement-part markings. This 1975 car may not retain every factory item.
- Open only for a real service job. Consult the correct Midget factory procedure for the fan, belt, pulley and timing cover before removal. The CAD explosion distance is a viewing aid, not an access path.
- Capture the untouched layout. With the cover off, photograph the timing marks, both sprockets, all shims, key, chain, tensioner pivot, washer and split pin before turning or loosening anything.
- Index the parts. Record which face of the cam sprocket points outward and which two of its four holes take the bolts. Photograph the lockplate tabs before they are bent back.
- Inspect before ordering. Count the real teeth and chain pitches; measure the actual crank nose and gear bore. Check chain, tooth and tensioner wear using the factory method.
- Use the proper timing procedure. The Triumph-family workshop drawing calls for checking sprocket alignment with a straightedge and using shims where needed. Marked and unmarked sprockets have different timing instructions. Confirm the procedure for this exact Midget engine; do not copy the virtual gear phase.
Source and parts trail
| Record | What it establishes | What remains open |
|---|---|---|
| Midget factory specifications, p. 12 | Single chain, 0.375 in pitch, 62 pitches; tappet 20.30–20.32 × 44.45 mm; cam journal diameters and running clearances; 0.12–0.216 mm cam end float. | Center coordinates, gear tooth counts and this engine’s wear. |
| Midget 1500 internal-engine plate, p. 33 | Distinct cam retainer, two fixing bolts, chain, tensioner with pin/washer/split pin, both sprockets, cam lockplate and two sprocket bolts. | Exact fitted variants and dimensions. |
| 119389 crank gear listing and 838-205 cam gear photo | 35 mm listed crank bore; photo comparisons for teeth and cam fixing-hole arrangement. | Photo counts and profiles require confirmation on the fitted parts. |
| Triumph shop manual, engine assembly | Shared-family comparison for straightedge alignment, cam sprocket orientation and marked/unmarked timing methods. | Confirm exact applicability and specifications for the Midget’s engine number. |