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Rick_Graham

How Difficult is it to true a crank?

3 posts in this topic

I understand the concept of truing the crank but just how much of a PIA is it? I can do it between live centers with dial indicators but just how much beating does it really take? I'd like a little insight since I'll be splitting the cases for the first time to fix a seized rod bearing. TIA Rick

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This is a very peculiar operation; it's done with dial indicators and a big heavy lead mallet. :naughty:

How much of a beating it will take depends on the crank. The bigger and stronger, the more they resist truing. You do NOT true them on the same surface or setup that you check them on. A sturdy surface with a lead or copper sheet over it, or real hardwood is what I've always used.

Checking should not be done using the center drillings at the ends of the axles, though, but on a stand where each axle is supported on a pair of rollers. next best would be to rest the crank on it's own mainbearings. This more nearly duplicates the crank running in place, and is more accurate than spinning between centers.

Having said that, if you don't have the right jigs to do the presswork, you shouldn't attempt it unless you're experienced enough to make something up. You may want to "sublet" changing the bearing and truing the crank.

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"Checking should not be done using the center drillings at the ends of the axles, though, but on a stand where each axle is supported on a pair of rollers. next best would be to rest the crank on it's own mainbearings."

Thats exactly the type of advice I was looking for :naughty:

" You do NOT true them on the same surface or setup that you check them on."

I guess I should have said "check it between centers" but that's the easy part. Fixtures and jigs can be fabricated as needed without a problem as I run a machine shop and these "government jobs" can be fit in from time to time :naughty:

Thanks for the advice grayracer513, you and others like you are why this place is so cool!

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