TE Lifetime Contributor
Main Motorcycle: Rickman T120
Join Date: May 2010
Location: Victoria Australia
Other Motorcycle: T160,TR6
The later cases had a little less interference fit on the outer race.It crushes the bearing less,so you can use a bearing with less internal clearance.
If you use the C2 bearing in early cases,there's almost 50% chance it will work OK.Not all cases are equal,and neither are all bearings.If it's not OK,there will be no internal clearance when the bearing is fitted in the cases and the inner race is fitted on the crank.The bearing will not turn easily without internal clearance,and it will fail.
If you try a tighter bearing (C2) and it doesn't turn freely,then you need a CN bearing.