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Another non M20 question

Hey fellas

I have acquired a basket case B31 with frame number ZB 4017 which I thinks puts it about 1949. Unfortunately there was no rear brake/hub assembly with the bike when I bought it. The rigid rear frame is very different to the BSA M20 frame I have noticed, so I don't think an M20 hub will fit into the frame.

By any chance would some one on this site know what type of brake/hub assembly I need to fit the bike and where I could find one?

Cheers

Neil

Re: Another non M20 question

This isn't an easy one to find..The hub is a 'one piece' design that was created by riveting the brake drum/ sprocket to the side of a cotton reel hub..Due to this method of assembly finding one with good teeth on the sprocket and a reasonable surface in the drum is essential because repairs are difficult/impossible...The brake plate and rear brake torque arm are specific to this model...

As well as the rear spindle, bearing adjustment nuts etc. and the wheel nuts there are also two chain adjustment cams...Wheel bearings are taper rollers....The brake shoes are the same as those fitted to later 7" brakes on the B31 etc. and at last those are readily available...I'll try to dig out an illustration of the assembly later...Ian

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

Re: Another non M20 question

Here's an exploded view of the rear wheel showing the part numbers and order of assembly...Ian

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

Re: Another non M20 question

I have a '52 M21 with that type of rear hub. I must have been lucky as the brake drum is in good condition and somebody prior to my ownership rebanded the sprocket. When I got the bike it was in pieces and almost a pile of junk. Somehow the sprocket was rebanded while still rivetted to the hub, so where there is a will there must be a way. If the drum was worn out then that would create problems. I found the rear bearings obscenely expensive in Australia and got a pair from Vintage bearings in the UK at a very reasonable price. They were modern bearings with a sleeve pressed in centre and worked perfectly.

email (option): tknalder@iinet.net.au

Re: Another non M20 question

The post war M Series hub which uses the same method of construction as described in my first post is not the same as the B Series type...In fact everything is different...

It is possible to 'retooth' the B Series sprocket but there is very little material to play with as the root diameter of the sprocket teeth is not much bigger than the drum...The drum itself is also very light and probably hasn't got enough material to skim the brake surface unless there is only light marking...

I went through all this many years ago on my 1951 B33 which I've owned for over 40 years and ultimately changed the rear wheel for a 'splined hub' swinging arm wheel...[See photo below]..Even doing that though the rigid brake plate and torque arm is still needed and the manufacture of a spindle, chain adjustment cams, bearing spacers etc. etc. is still required....

One problem with the M Series assembly that I've come across twice (once on my own M33) is failure of the rear spindle...They both broke where the spindle transitions from a taper to a parallel section. This spindle is unlike the WD one and quite hard to find so it's best to look out for a spare just in case!!....Ian

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

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