BSA Owners' Club Forum

The BSA Workshop => Singles => Topic started by: WayneBergman on 14 July, 2021, 05:01:15

Title: Burman gearbox
Post by: WayneBergman on 14 July, 2021, 05:01:15
My 52 BSA B33 is from time to time popping into neutral when shifting. It never slips out of gear into neutral when under load but it seems to happen only when upshifting. On my list for things to work on in the fall is sending the mag out for a rebuild and taking a look at my gearbox to see if I can find the source of the problem and have a good look at the insides of my gearbox. The bike is new to me in the last 6 months so finding things out as I go.
Photo attached show my gearbox, I have been told by a friend that knows a bit about BSA's (mostly prewar) that I have a Burman gearbox but he is not sure what model the gearbox is. Before I take the gearbox apart I will want to know what year the box is or some kind of identifier for the gear box if I need parts or support literature for guidance on the rebuild. So a couple of questions please.......
1......Can anyone tell from the photo what year or model number my gearbox is?
2..... I use straight old school 50 weight oil in Engine, Primary and Gearbox. Any chance using something different than the 50 weight in the gearbox will help from the box wanting to find neutral.
3......Also when I bump start the bike I normally put it in second gear, pull in the clutch and push to speed and then off we go - but lately the bike will fall out of second into neutral on its own and it never used to do this.

My guess is the cam shaft that moves the selector fork on the lower layshaft is allowing the first and second gears on that layshaft to somehow slip into the neutral position. Any tips much appreciated........wayne
Title: Re: Burman gearbox
Post by: Pete C on 14 July, 2021, 07:09:28
To me it looks like the standard BSA box used on rigid or plunger bike in the early fifties. They will jump out of gear when wear sets in or they are poorly adjusted.

If you let me have your e-mail I will send you a file that has fairly comprehensive information and instructions on examining and rebuilding these gearboxes. Most of it I pinched from contributors to the WM20 forum at

Title: Re: Burman gearbox
Post by: Jim S on 14 July, 2021, 13:47:19
Hi Wayne
There are lots of previous posts concerning the B31/33 gearbox including this one:
Do a search on b33 gearbox for more info.
I doubt that changing primary or gearbox oil type is going to help your problem, but most people put a lighter oil in the primary.
Title: Re: Burman gearbox
Post by: Calum on 14 July, 2021, 20:54:03
The info Pete has is very useful, mainly for checking bush clearances etc.

If it is jumping in and out of gear it will no doubt be worn selector forks/dogs, and/or excess end float on the selector cam shaft. Mine would pop in and out under load sometimes though, but usually the overrun.

If you're having trouble with false neutrals or finding the gear then the selector mechanism may be at fault too. You'll only really find out by working through the gearbox and looking at what moves (or doesn't)
Title: Re: Burman gearbox
Post by: WayneBergman on 15 July, 2021, 04:59:53
Thanks a bunch Pete, my email is ...wayne
Title: Re: Burman gearbox
Post by: Mike40M on 15 July, 2021, 06:21:34
It seems this thread evolved from Burman to BSA gearboxes. Anyhow a short note on some  Burman gearboxes, e.g. the one used on Vincent Comet.
They leak a lot if filled with oil. With semi fluid grease which they should have, almost no leak.
Title: Re: Burman gearbox
Post by: Pete C on 15 July, 2021, 21:27:07
This however is definitelya BSA gearbox and on no account should you use grease as lubricant! Oil only, otherwise it will have a short life!
Burman boxes (some) are very different beasts in this respect.
Title: Re: Burman gearbox
Post by: WayneBergman on 15 July, 2021, 21:51:08
Great info folks and thank you all for this. Looks like it is a BSA gearbox then so this is good to know......wayne