thanks bikermike, that info has absolutely convinced me I was lucky enough to buy the right wheel for the b31, my sprocket has 40 teeth but is dimensionally the same as yours.
Thanks Brian very much for those pics, I will print them out and show them to my engineer guy, I have a lathe (pre war southbend) but I cannot get the accuracy to make those parts myself.
Once I get the wheel done can get on with the rest of the bike, it did look at one stage I was going to have to adapt a plunger wheel to fit!
I'm really glad I asked for help on this forum, as far as I know there is no forum for the b31/33 range, Ive done quite a bit of searching but not found a specialist forum for the pre unit bsa singles.