It is both an engine stop AND a decompressor for starting. For starting from cold, tickle the carb 2 or 3 times, push the choke lever forward, if it as one, and retard the magneto a smidgen.Then pull in the valve lifter lever and turn the engine over a couple of time with the kickstart. Release the valve lifter and gently turn the engine until you feel the kickstart come up against compression. Pull in the valve lifter lever again and gently push the kickstart down a few inches. Let go the lever and bring the kickstart up again. Then give it a good kick and if all is well it should start.

I was at the Belgian Classic TT races in Gedinne a few years ago and there were a few rigid framed BSA racing, all highly modified. The one in this (not very good) photo clearly has a swinging arm gearbox, presumably using a set of special engine plates have been made to fit it. The bike was listed as a ZB33 but has an alloy top end, girder forks but an 8" front brake.
If you have the resources anything can be done.

I thought I'd show a couple of pictures of my 1948 BSA B32 Competition.
As it was when I bought it last summer and one after a bit of work over the winter. Next winter's job is to change the front rim for a 21" and mudguard and stays to suit (if I can find them).

I think we've drifted from the original topic here, but this is what I've done to restrict the upward movement of the brake pedal. The bracket doesn't need to be super strong as there's little pressure on it. The bolt allows for any adjustment and the rubber prevents metal to metal contact.

I like that. It's given me ideas about doing something similar for my rigid B32. The pedal is higher than I'd like and stops against the footrest with a clank when I release the brake.

Back in the '70s a friend of mine ran a plunger A10 sidecar outfit on paraffin. I kept a squeeze bottle of petrol in the outfit which he would fill the carb with to get it started then turn on the tap for the paraffin in the tank. It seemed to run ok, although perhaps a little hot and with a characteristic smell.

One can always make the brushes smaller.

Correct. I couldn't find brushes for an E3HM anywhere so filed down E3L brushes to fit. Very easy.

Quote from: Derek996 on 11 March, 2022, 19:46:47

As I see it. The original capacity is 247cc and the compression ratio is 9.5:1. The combustion chamber volume = swept volume (247cc) / compression ratio = 26cc.
A 10% overbore takes the swept volume to 271.7cc , so the new compression ratio is 271.7 / 26 = 10.45:1.
I'm sure someone will correct me if I'm wrong but it can't be far out.

The above formula is not quite right as compression ratio = (combustion chamber vol + swept vol) / combustion chamber vol. This gives a combustion chamber vol of 29 cc.

The difficulty in predicting the CR of the enlarged bore is that the piston shape may have changed and therefore the combustion chamber volume may be different. In fact, it's possible that the new piston shape may have been designed to give the same CR - without specific design info on the new piston, it's difficult to know

On reflection I see that you are right. I just did it of the top of my head without fully thinking it out. I also assumed no change to the piston crown which would make a compression change by itself.