I'll show my ignorance of metallurgy for once. I always accepted that where two parts were designed to be running against each other, the materials chosen were two different metals, hence the usual steel against brass, bronze or aluminium. Wear happens, fact of life, the softer bearing material is cheaper and easier to replace than a finely crafted complex shaft.
In this case a softer brass or bronze washer should work, sandwiched by the layshaft on one side, big first gear on the other. It is not under any real heavy load, acting more as a spacer. I can only postulate BSA tried this in development as being cheap and easy to set things up but that wear on this soft washer proved troublesome and hardened steel was chosen by the BSA boffins as a reliable fix.
Maybe Julian has something in the archives?
Swarfy.
