BSA Owners' Club Forum

The BSA Workshop => Singles => Topic started by: FLACTEM on 07 February, 2018, 18:36:45

Title: B25 gearbox assembly
Post by: FLACTEM on 07 February, 2018, 18:36:45
Hi, I'm using a Haynes manual to help with the reassembly of a B25 (1968) gearbox.  However, although the text if helpful there is a lack of diagrams andpics, so any additional information would be welcome.  Thanks, Flactem.
Title: Re: B25 gearbox assembly
Post by: AWJDThumper on 07 February, 2018, 19:00:49
You can see the basic layout from the parts book diagram. Just ask if you need any advice but basically most of the later BSA unit single gear boxes are similar.
Title: Re: B25 gearbox assembly
Post by: BEESY on 07 February, 2018, 20:32:49
Do you mean the assembly of the parts in the correct order or putting the gearbox back into the crankcase?

There are a few videos on you tube showing the technique of putting the gearbox in that I found useful.

You basically assemble everything together on the outer cover and push it all back in at once.

Remember there is a spring attached inside the crankcase that you need to push against. The knack is knowing if you just need to push harder or if something isn't lining up correctly.

It took me about 20 mins to get it right.
Title: Re: B25 gearbox assembly
Post by: AWJDThumper on 08 February, 2018, 07:31:38
As said, it's a lot easier to assemble everything on the inner timing cover first and then slide it into place. That way you can check everything is properly located especially the selector forks. Make sure you include the two thrust washers/shims - nos 94 and 100 in the parts diagram. Once assembled, it's best to check you can select all the gears.
Title: Re: B25 gearbox assembly
Post by: Editor on 08 February, 2018, 12:33:18
My advice would be to junk the Haynes Manual as for the unit singles it is quite frankly pathetic!
Get yourself a copy of Rupert Ratio Unit singles manual vol 1 the engine which are back in print now:-

Vol 1 23.95 inc uk postage
Vol 2 25.95 inc uk postage
Vol 3 back in print soon...
All available direct from Ratio Publishing.
Authors signed copies only available from http://www.ratiopublishing.co.uk
or email ratiopublishing@gmail.com

They cover everything you will need to know. No rebuilder of unit singles should be without one!
Chris
Title: Re: B25 gearbox assembly
Post by: AWJDThumper on 08 February, 2018, 12:46:51
Here's a couple of animated CAD videos to show how to put a Starfire gearbox back together.

https://www.youtube.com/watch?v=4_LMTyA49Ec

https://www.youtube.com/watch?v=7Q6R-C4z86o

Title: Re: B25 gearbox assembly
Post by: JulianS on 08 February, 2018, 13:26:52
You can download for free Unit singles factory (not Haynes) workshop manuals, parts books and more from this website.

http://www.bsaunitsingles.com/owners_repair_manuals.htm


When I owned unit singles I found that the Rupert Ratio books were the most useful publications.