Hello all & happy Christmas!
I’m struggling to identify exactly what model of BSA my gearbox is from!
It appears to be standard enough but looking though the gearbox technical section, none of the case/cover part numbers tie up with any of the ones listed.
Can anyone help to ID please?

We have-
main case appears to be 36-3147, maybe 36-3141??
Inner cover - 66-3129
Outer cover - 66-3126
As always, any help appreciated!

email (option): gino_kerekes@yahoooo.co.uk

The cast-in numbers will always be just that - casting numbers - and will differ from the number allocated to the finished article.

Looks like you have a gearbox from a plunger frame.

Tim W

email (option): t.j.walker@btinternat.com

These gearboxes were fitted to post war rigid and plunger model B Series bikes from 1948 onwards and rigid and plunger, tele fork, M Series bikes from 1948- 1963...Ian

email (option): ian@wright52.plus.com

As always,
Thanks for clearing that up!
All the best,
Gino

email (option): gino_kerekes@yahoooo.co.uk

To expand on what Ric said and worth remembering
BSA ( or a BSA subsidury) made nearly all of their own parts.
parts were made in batches, not as required by production .
Thus the foundry might do a run of 20,000 gearbox shells , place them in a stillage ( or two ) and sit them in a corner till the machine shop was ready to machine them .
Because BSA borrowed every penny needed for the following years production, these parts had to be accounted for on the factory inventory as Midlands bank had rights over them.
Thus the castings / forgings all got numbers for the raw casting/ forging.
As they were finished, their value increased so they got new numbers, usually 1 or 2 larger than the raw numbers.
We also have to remember that the same raw part could be machined differently to make different parts for different bikes thus a casting number could have multiple part numbers. Gear box shells is a prime example of this.
Top steering clamps are the perfect example as they will have different machining for different models.

email (option): bsansw1@tpg.com.au