Difference in layshafts

[Martin s]

Hello, wondered if anyone knew why these 2 layshafts are different?
One is from early 125 special and is dished on the end, and one is from a late 125 special
and is flat?? Both engines seemed untouched when stripped. I think the dished one was from the earlier engine. Would it make a difference using either?

[Warkton Tornado No.1]

It’s almost certain that the ‘dished’ version will be the later of the two, but there is no difference as far as the use.

The ‘dishing’ is there for two purposes, both to do with manufacture. The engineering term is called relief.

If you look @ both you will see a cross hatch pattern. This is the evidence of final grinding as the parts will have been hardened by that stage.

The relieved layshaft has less cross hatched ‘land’ so will have been easier to produce.

Additionally, the relief makes the component stronger, despite there being less material, simply because the finished shape has less sharp corners & flows better from plane to plane.

Sharp corners are stress raisers.

[Martin s]

Useful insight thankyou.