BSA B21 REVIVAL
Last month, John Lay began the reconstruction of what was once a 1937 BSA 250 single. There are no new spares anywhere…
Last month, John Lay began the reconstruction of what was once a 1937 BSA 250 single. There are no new spares anywhere…
After refurbishing a set of forks, an examination of the frame was called for. This, apart from dirt and some surface rust, proved to be in quite good condition. Good, that is, with the exception of the rear wheel mountings at the end of the chainstays. These were badly worn, out of shape, oversize holes with stripped threads. Much work with the welding torch was called for, rebuilding the wear, straightening out while hot, re-drilling the holes and re-cutting threads. An angle grinder was used to reshape the built-up weld, and then all was covered in a coat of anti-rust paint.
As the frame and forks were together it seemed appropriate to fit the wheels. This would allow the BSA to be rolled in or out of the workshop, instead of me carrying it, and I could get it up on to the workbench. The rear stand was missing, so I made a simple wooden frame which located onto a length of bar passed though the engine plates. With the bike in place, my attention turned to the rear wheel. This appeared complete, still fitted with a Dunlop Universal tyre. Amazingly it pumped up and stayed up! So that was left for the time being, to be replaced with a new one when the bike was ready for the road.
Complete the wheel might have been, ready to be fitted it was not. On removing the brake plate I found that not only was the sleeve for the actuating cam detached from the plate, so was the shoe pivot pin. Incredibly, it was clear that someone had continued to ride the bike in this state! The shoes can’t of course get out of the drum with the wheel in place, but with nothing keeping in them line with the brake plate you can imagine the result…
The brake’s shoes were completely knackered. Happily there are lots of British bikes about with 7” brakes so this didn’t look like much of a problem. As luck would have it, a genuine set of NOS shoes turned at a jumble, so the original pivot pin could be used after all. But where to fit it? The pivot needs to be in the correct position, otherwise the shoes will not be centred within the drum. As the hole within the brakeplate had become somewhat enlarged, this might be tricky. The answer was to make the brake ‘fully floating.’
To do this the pivot was popped into the lathe, faced off, bored through and taped 5/16 CEI, then secured to the brake plate with a large flat washer and a suitable bolt. Because the hole in the plate is oversize, when the brakes are applied the shoes will move into the correct position. They have, in effect, become self-centring. With the brake held on, do up the bolt and there you are.
However, this wasn’t the only challenge. A large, triangular-shaped piece of steel is riveted to the brake plate and this forms the anchor which prevents the plate’s rotation when the brakes are applied. This in turn is connected to the torque arm below the chainstays. Movement of the plate had caused this to be in contact with the rear drive chain and it had worn away on one side, almost to a knife-edge. So more welding up and grinding were required.
Before putting everything back together, the wheel bearing were examined. These are cup and cone type and, once the considerable amount of old grease, dirt and general crap was removed they appeared to be OK. They were repacked with new grease, the whole assembly was put back together, and the wheel fitted to the frame.
Now to the front wheel. With the old tyre removed, I discovered that it was the wrong