| Diagram | CHAINCASE AND CHAINS |
| Subsystem | primary |
| Listed in parts books | Not catalogued by year yet |
Gearbox sprocket (18 th)
An 18 tooth gearbox mainshaft sprocket listed in the chaincase and chains section of the parts book.
This is a gearbox sprocket, 18 tooth, listed in the chaincase and chains section of the parts book. It's the sprocket that mounts on the gearbox mainshaft and carries the primary chain.
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The catalog only shows this one appearing once, tied to a 1967 listing, so we don't have a broader run of years to point to. If you're matching this against your bike, best to confirm the tooth count and fit against what's currently on the mainshaft before you order.
The manufacturer code on file for this part says Lucas, but Lucas made electrics, not gearbox sprockets — that tag is almost certainly a mismatch in our records, not a fact about who made this piece. Treat this as a mechanical primary-drive component regardless of what the code says.
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