My own personal preference for the bearing fit on the main shafts:
Outer ball bearings - hard push fit. If you need to bash the cases to get them together, it is too tight.
Inner roller bearings - press fit and should require some tapping to get them on to the shaft. If they slide on, I either replace the shaft or loctite the bearing on.
Thans fir your response. I'm assuming you just reduce the crank shaft size towards the ends to allow a greater clearance for the roller bearings?
Glenn
No I don't touch the shafts to make the diameter smaller. A little too tight is OK.
If you have shafts made to the correct dimensions, not bodged or worn out and good quality bearings, everything should fit together as is. BSA when making the bikes did not have someone modifying the shaft diameter to make the bearings fit. The motor went together as fast as possible.
On these old bikes, I mainly have to deal with main shafts that are too small from years of abuse and bearings spinning. If the roller bearings are a little too loose, I loctite them on. It the ball bearings are too loose, I replace the shaft as you can't loctite the balls on or you can never get the motor apart again without great difficulty.
