| Diagram | Fig. 5 — GEAR CLUSTER · ref 30 |
| Listed in parts books | 1969–1970 |
BSA Lockwasher, mainshaft
A lockwasher for the gearbox mainshaft, used to keep the mainshaft retainer from loosening.
This is a lockwasher for the mainshaft in the gearbox. It shows up in the parts-book listings for the gear cluster and for the footchange/footstart mechanism, which tells you it lives inside the transmission where the mainshaft is retained and needs to stay put under load.
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A lockwasher like this does one job: it keeps whatever nut or retaining piece sits against it from working loose as the gearbox turns over. It's a small part but not one you want to skip or reuse if it's tired - once a lockwasher's tabs or teeth are flattened out it stops doing its job.
Our catalog record ties this to gearbox work spanning 1969 to 1970 in the listings we've got, but it doesn't spell out an exact model. Confirm fitment against your gearbox before ordering, and give the shop a call if you're not sure this is the one your parts book shows.
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