| Also known as | AA81, E8785 |
| Diagram | Fig. 14 — PRIMARY TRANSMISSION AND OIL PUMP DRIVE · ref 25 |
| Subsystem | engine bottom |
| Listed in parts books | 1969–1974 |
LOCK WASHER ENG SPROCKET
A tab-style lock washer that fits under the crankshaft sprocket nut to keep it from loosening.
70-8785 is a lock washer that fits over the engine sprocket on the crankshaft, keeping the retaining nut from working loose once it's torqued down. It's a tab washer style, meaning it locates against a flat or feature on the shaft and keeps its own orientation so it can't spin under vibration.
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This part shows up in our records under the legacy AA81 number as well, so if your parts book lists it that way, it's the same physical washer. We don't have catalog appearances logged for this one on our end beyond the basic listing, so if you're working on a triples-engine Triumph or BSA, confirm the fitment against your own parts book before ordering.
It's a one-time-use kind of part in practice - once a tab washer has been bent over to lock the nut, it's not something you want to reuse. Keep a spare on hand if you're pulling the crank sprocket for service.
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