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BSA B31 gearbox

Posted: Fri Jun 03, 2016 10:08 pm
by Looper
Hi all, I've got a question with regard to my gearbox. The bike is a 1950 B31 plunger that has what looks like an M series gearbox. The kickstart spring broke so I ordered what I thought was the right part, a M/B series spring OEM: 66-3058. The spring was way too big, and what came out looked like a B series spring. I bodged it in rather than order a different spring that might also have been wrong. It meant cutting of part of the hook that locates with the quadrant as it was fouling on the inner cover. What I'm wondering is was there a transitional gearbox fitted to B31s before they changed to the B series gearboxes, or do I have a different gearbox altogether, or did I just order the wrong spring? I'm only really concerned about it because next time I order parts for it I want to be sure they're right. Thanks.

Re: BSA B31 gearbox

Posted: Fri Jun 10, 2016 10:27 am
by Looper
I might have answered this one for myself. I'm beginning to think I have a 1946-1948 B-series gearbox, nearly the same as the M/B but with several different parts. Does anyone know a way to tell for sure? Thanks.