Crankshaft and new bearing

[raspersyd]

Hi Gents,
I have now got the new bearings in the crankcases and I come again to this forum for advice. The crankshaft on the left hand side does not fit into the new bearing as it seems to be slightly too tight. Is there an easy way to adjust this? I am sure it is the correct bearing as it was bought from a proper dealer/supplier.

If anyone has suffered the same problem it would be great to hear how you got past it.

[Rick]

In the US, bearing fits are often classified as 'interference' - it's possible to wiggle it onto the shaft, 'light press'- requires more force than a person can apply, or 'heavy press'- that will require a hydraulic press and shouldn't be done if the race isn't firmly supported. Your bearing should be an interference fit- tight but possible. I have better luck feeling the journal on a shaft for burs/dents than using micrometers. If you can feel any defects on the journal surface you'll need to remove them- a small, 1/2"x1/2"x3" fine polishing stone is a standard tool in most machine shops- a file is OK, and sandpaper is more likely to follow a contour than remove it. Lightly 'stoning' the surface will usually make defects obvious the same way a body man uses a file to find small defects in a body panel. When you're confident that the shaft is smooth and round, put it in a bag, throw it in the freezer overnight, and it will probably slide in. It only takes a couple of tenths, as in 0.000X", to make a big difference- the shaft won't contract much from freezing, but it doesn't take much to make a difference.
Sometimes the case bore is so tight that pressing the outer race into the case actually deforms the whole bearing- not too likely with an aluminum case and a small bearing.
Last, don't drive the shaft onto the bearing- try to apply any force to the inner race of the bearing, driving it onto the crankshaft Pounding on the crankshaft can damage the bearing races- the balls dent the races- do a Google search for 'bearing brinelling', and don't do it.
Feezing the shaft will probably work- there are some aerosol can tricks but the freezer does it for me.
-Rick

[cgrace]

Heat and cold can definitely make a difference. Warm the bearing and freeze the crank.

Chris

[kmev]

When I picked up my newly-rebuilt crank and bearings from Syd's Cycle, Malcolm told me to hone the crank journals with emory cloth until the bearings would slide on. I did this before I installed the bearings in the case.

Allowing the crank to slide into and out of the bearings makes life much easier when shimming the crank, but don't make it any looser than necessary.

[raspersyd]

Hi Guys,
Thanks for the comments and I think you were all on the button. The problems seemed to solve itself this after noon. I have been puzzling what to do for a couple of days and went back into the workshop this afternoon. We've just had a day well into the thirties and blow me if the crank didn't slide straight in on the first go.
Now to buy a dial guage tomorrow and get it and the gear box shaft shimmed up.
Thanks again

Syd