The BSA Workshop > Singles

B40 Swinging arm and a few questions.


New to this forum.
Recently bought a B40 ( 1961) which needed tidying. Came with a 12 month MOT so was usable.
However, I started dismantling with a view to repainting etc and everytime I remove something, a new problem arises.
At present the bike is just a frame with the engine in. I would appreciate a bit of advice on:

1. The swinging arm is solid - I cannot move it in the frame! I assume the pivot axle is seized. Any advice?
2. The battery box has virtually rotted away so will need rebuilding. Has anyone got a photo of what it should look like so I can get an idea of what to make?
3. How heavy is the engine  ? is it easy to lift out without any help?
4. Where is the best place for parts ?

1. The swinging spindle is a tight press fit in the frame, add possible corrosion, removal is for the brave. Best done by a proper press. If you use a hammer and drift beware burring the ends.

When it is out the next issue is remove the bushes in the swinging arm, you may get them out with a drift or press or carefully saw a slot.

Then fit new bushes which will need to be line reamed to suit the new spindle.

Then press it all together not forgetting the spacer.

The Rupert Ratio Unit singles manuals very helpful.

2. Parts book useful. See photo from 1961 parts book.

3. Engine unit listed as 35 kg.

4 I use C and D Autos  for many of the parts I buy. Very helpful and knowledgable if you phone them

Thanks for the quick answers.

It appears that I've got to completely strip the bike to get the frame to have the swinging arm looked at and the pin pressed out if possible.

One other quick question; does the pivot tube at the top of the rear part of the frame just push out with a bit of persuasion?



The tube should be a tight fit and when assembled the nut and bolt needs to be quite tight or the handlng may suffer. You may be able to drift it out with care.


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