I have managed to stem the oil leak (flow) from the engine on my 43 WM20, but only while the bike is upright (and on stand). When I have the bike leant over to the left on the side stand the leaking starts on the left of the bike. I believe this indicates the tranny main shaft seal.
My question is, looking at the diagrams for the tranny it appears the main tranny seal and washer are on the inside and so I have to dismantle and pull out the whole tranny and gears to replace it, is this correct?

Thanks for any help.

Yes indeed Joe you have to strip the box to fit a modern double sealed bearing (I remove the inner seal). Also the sleeve gear bush #54 might be worn which could also allow oil to pass. Ron


delete ebay

email (option): ronpier@talk21.com

Thank you so much for the reply .

It is too big a job for me so I’m going to try and just live with it (and not put the bike on the side stand, lol)

Cheers,

Joe.

The gearbox without any form of working seal (in other words a standard box) can lose its oil very quickly, reaching a level that is low enough to result in premature wear of various components...

I would recommend you check the level and top up as required every 300-350 miles maximum...Ian

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

Thanks for that.

Joe.

Does anyone have a step by step write-up on how to change this seal (Haynes manual style?) for the main tranny, I know it entails taking the whole thing out.

Also can someone let me know the product number and where I can obtain one to replace the seal with a modern double one.

All help will be gratefully accepted. I will need to do this myself as I can’t find a mechanic that works on old BSAs near me here in Arizona.

Thanks,

Joe.

email (option): Se98jl@hotmail.com

Hi Joe,
Have a look in the tech docs section, some good pointers there.
The bearing you want is 6207RS or 62072RS(and pop out one of the seals), not very expensive at all, £5.50 in the UK.
https://www.bearingboys.co.uk/Dunlop-Ball-Bearings/62072RS-Dunlop-Sealed-Ball-Bearing-1903-p
Scott

email (option): larkesATgmail.com