always had a shop do this to make sure a crank was good, but i have one i think is bad and want to save the time and expense of taking it to a shop. do i check it sitting in the top half of the main with the caps removed? seems to me the caps might pull the crank straight if it was out a little. would it be better to set the crank up between centers (since i have a lathe) and check it that way? shouldn't be too hard to figure out if it's bad but i got hung up thinking about the main caps making a bent crank straight, of course the bearings would wear faster i'd think.

------------------
ICON Motorsports
1st & 3rd
MM Black Diamond 538 F&AM

 

You can lay it in just the front & rear main bearings in a block, and check the runout with a dial indicator; or do it in a lathe.

It has to be kind of alot to hurt the bearings very much, as the force required to bend the shaft a couple of thousandths is rather small. What I'd mostly be worried about is grinding on a bent shaft; because it would have runout in the grinding lathe, and then the journals would be ground opposite to the bend... sure the journals might be straight, but then the throws could be off just anywhere...

They're easy to straighten though; in machine shops, I've seen people do it with a couple of wood V-blocks and a hydraulic press, and also with a dead-blow hammer. I don't believe I'd try to do a cast one for fear of breaking it, only a steel one. Find the runout with the dial indicator setup and then have at it, and recheck often. They're easier to bend than most people think. Legend has it that some cranks (especially older steel ones) will bend just from sitting on their side on the ground if you put something heavy on them.

------------------
"So many Mustangs, so little time..."
ICON Motorsports