| Also known as | E3902 |
| Diagram | Fig. 1 — CRANKSHAFT AND CONNECTING RODS · ref 39 |
| Subsystem | engine bottom |
| Listed in parts books | 1963–1964, 1976–1980, 1983, 1985 |
Plug, crankshaft oilway
Small plug that seats into the crankshaft oilway on Triumph twins to seal off a drilled oil passage.
This is the small plug that seats into the crankshaft oilway on Triumph twins, part number 70-3902, also known by its earlier form E3902. It shows up across crankshaft and connecting rod figures in the parts books, which puts it right where you'd expect - down in the crank itself, blocking off one of the drilled oil passages so oil pressure gets directed where it needs to go rather than leaking out an open end.
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It's a small, unglamorous item, but it matters. If it's missing, cracked, or was knocked loose during a rebuild, you can lose oil pressure to the journal it's supposed to feed. Anyone splitting cases or doing crank work should check this plug is seated properly before buttoning the engine back up.
Our catalog record doesn't tie this part to one specific model or year - it turns up across multiple crankshaft-related figures over a long span in the books. Confirm which crank your engine has before ordering, and give the shop a call if you're not sure.
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