I’ve had 2 crankshafts rejected by the machine shop. One had a bad journal which I should have seen, and the other the thrust was out of spec. When I go to look at another one, how can I measure the thrust? I can measure journals and find specs for that, but not real clear on the thrust.

 

My engine builders software shows the thrust width to be 1.200 " The best way to measure it is with a snap gauge and then a micrometer to measure the snap gauge.

To be honest with you most of the time you can tell if the thrust is ok by feel and visual appearance. The thrust surface should be very smooth and flat. Any wear is typically on the back side as the crank is mostly being pushed forward. Pretty rare to see the front side worn. If you have an old used main bearing for that position you could probably use it with a feeler gauge for a quick check too. The clearance should be between .004" and .010"

Used crankshafts are always a gamble. They can look perfect and still be cracked when you magnaflux them. You almost have to get some type of agreement from the seller that if it is no good you will get your money back. If you agree on a price I would have them take it to your machine shop and have it checked first. Its a tough one

 

Crank shafts can be checked for cracks quickly by "ringing" them. Hold it up by the rear flange and tap it with a light metal object. If it rings like a bell, it is usually (usually, not a perfect way ot tell) not cracked. If it had a dull thud sound, it might be cracked. Should be magnafluxed to verify.

 

As mentioned, a pair of calipers is the best way to tell if a crank is usable. If the journals measure standard (stock measurements) and there are no serious scratches or gouges, assuming the crank isn’t cracked or bent it should be usable.

If the crank has been turned undersized, the same guidelines apply, you just have less material to work with. If the crank is already .030, that’s the end of the line, I don’t think you can get bearings for a crank cut further than that.

 

Ok thanks guys, yeah Bill, the one crank actually had a ridge you could feel on the thrust surface, but I didn’t know to check that beforehand. I just may take a main bearing and check the clearance, seems like an easy check.