Layshaft bearings

One of the things I find difficult to understand is why its necessary to shim the layshaft for the roller bearing and NOT the ball bearing(although rollers do need to be contained),especially when we are told that the ball bearing needs to be a hand fit to the shaft,unless the ball bearing is wider than the roller. Then it makes sense. Except then we should be shimming between the roller and the fixed gear,and not behind the kickstart.In any event If the bearings are the same width and a hand fit it makes no difference and the shaft needs shimming in both cases. Mine certainly needs it with about an 1/8th of an inch of end float which has allowed things to get knocked about.And no the kickstart bush is not worn .I'm thinking of making up 2 equal shims, one to go in the kickstart shaft against or behind the bush and one against the roller. What do you think??.

Thanks James for the section detail. The only way to measure end float is with the Ks shaft and inner cover installed.The area that gives me concern is the junction between the third gear free pinion and the second gear ,at this point any axial loading from the shaft to the 3rd pinion is carried on a tiny area of the 3rd from the splined end of the shaft.,the bronze bush of the 3rd is also undercut with an annular recess at the ends(for lubrication?) which means it can't help.My gear has suffered here.There should not be much axial loading but any impact on the KS shaft (intentional or accidental) ends up here.I am also curious about the fit of the fixed pinion at the end of the shaft against the 3rd gear, in my case this has to be driven on with a hammer and socket but with care to avoid trapping the 3rd gear.Is this normal?.I also need to check the bush in the KS shaft ,althogh no symptons of wear it appears too short.

Hi Jim, Mine looks like yours!( so much for tiny axial loads!), But I notice that your bushes are not undercut at the ends, Does this mean they are meant for somewhere else?.They look better for thejob.

Hi Jim, No I was not thinking that. I was looking at the small nicks in the end of the gear I have a few extra ones, some may be the end of the oil scroll,but i have a few extras. The Box is back together ,after fitting a few new parts, I was left with 71 thou end float,I used a 50 thou spacer between the roller inner race and the fixed pinion and a 20 thou shim behind the kickstart. I have finished up with 1 thou end float,A bit tight!. The box works ok though I'm wondering if the selector fork has enough play to not be in continuos contact.I may strip it again to reduce the roller spacer. I'm sure these boxes must run normally with about 50 thou end float,which is probably concealed by the layshaft being a bit tight in the std ballrace in the back of the case.

Back together and working, the change is still not the "knife thro butter" we hear about. But i can now get neutral at a stop.Its a bit stiff at times through the gears so I'm thinking of looking at the cam plate plunger and spring next.