Gearbox mainshaft bearing, inner cover

.......or it simply needs reaming after installation to get the right class of fit perhaps.

,I had the same problem on my dommy ,the new layshaft bearing felt notchy after fitting,I removed it and fitted another bearing after polishing up the outer race surface and releaving the ally housing with some emery paper. I think I used a c3. The fit is too tight. Don't know if you can get a C4?.

Is the new bearing notchy before you have fitted the mainshaft? I would be surprised if the alloy casing could compress the outer bearing ring to the extent that it affects the bearing clearance.

My bearing was fine untill it went in, I used it for a few thousand miles and it stayed notchy , I removed it and it felt fine,I replaced it and the new bearing was the same ,notchy untill i took it out and releaved things , Either the c3 clearance was only a C2 or most likely the worn out victorian machinery at Norton was not doing the job. And AMC /Villiers just went along with the wrong measurements. They cocked up plenty of crankcases for sure.

Hi, I read this with interest as I have three gearboxes to sort out. I believe that the original bearings had a larger inner radius than the far eastern bearings now common. It is worth measuring mainshaft abutment lengths, as quality control was not good in those days in British Industry. Trust me , I used to be a Quality Consultant at one time. Many draughtsmen did not know about accumalative tolerancing. BMC A series engines had a normal 0.005 thou difference in main bearing bores, and, the crank pins were also 0.005 thou. misalighned more often than not due to knackered machinery and bad management practices. Do not forget that gaskets are not all the same thickness or material. I assemble the gearbox and check what size feeler gauge fits the gap, either it will be OK or the gasket is too thin. Sometimes I shim gaps, or turn off over length shafts to suit. Best regards, Paul

I did not have any problem with shafts fitting bearings (did not use any Far east stuff!) however if it has to come apart again I would not use the roller bearing conversion on the drive side of the layshaft as an uprated ball from Hemmings is fine on a Dommy and will not need the shimming that the roller does . Check the shafts for straightness.The inner cover needed a lot of heat to fit the bearing ,that should have made me think.