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Little issue pulling motorcycle crank bearings

F

fastline

Member
I feel like such a rookie again! Built engines professionally for a decade but I never made a mistake this stupid.

I am rebuilding the bottom end of a 2 stroke. I threw the crank in the freezer as I always do but somehow thought it a good idea to stick the bearings on the crank first. After I realized my screw up, I figured I would try to freeze the whole deal and heat the cases to get it together. No go. Bearings gotta come off the crank and be installed in the cases first.

I typically would use bearing cups to pull the bearings but this crank is a little special with sheet metal covers.

I am curious, I would estimate the interference fit to be around .0002" so I was wondering about methods to heat that inner race fast enough to get them to fall back off?

In the past I have used the red hot piece of pipe trick to transfer heat to the race but not sure on this.

any thoughts or ideas?
 
I used to remove the crankshaft bearings in model airplane engines by putting the crankcase in the toaster oven. The aluminum case expanded faster than the bearings and they'd fall out.

One time I was given a crankcase that someone had gotten a bearing in crooked, and that trick wouldn't work on its own. What eventually worked was spraying the bearing with WD40 to cool it and shrink it back down. Then it fell out and I was able to save the crankcase.

Not sure if you can figure out a way to apply that to your situation, but nobody else has had any suggestions yet...
 
Yes, Aluminum expansion rate is about double what steel is so heat works well. However, this is steel on steel. I have been here before with basically a good bearing on a shaft and no way to press it without damage.

I know there is a way because companies face this issue daily. Just need to find the right sauce. I would like to imagine a micro induction heating unit that I would focus energy only to the inner race.
 
Off the wall idea, but sharpened tips on a carbon arc torch to let you reach just the bearing, with the amps
cranked down?
 
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