Re: To turn crankshaft or not to turn

Posted by Dave C. on March 26, 2002 at 07:04:00 from (153.91.1.194):

In Reply to: To turn crankshaft or not to turn posted by Dave on March 25, 2002 at 16:58:05:

Dave, there are three areas of concern when it comes to cranks. 1. Are the journals smooth? Yours sounds like it is. 2. Are the journals round?. The only way to really tell completely accurately is to chuck the crank up in a turning lathe and put a dial indicator to it. It should be round within .0003". Since the bearing to journal clearance is about .0015" to .002" that doesn't leave a lot of variance. 3. Is the crank straight? Again, you chuck the crank up in a lathe and put a dial indicator on the main journals. There shouldn't be any more than .001" runout on the crank itself.
Other things to think about. Is the crank cracked? You may not be able to see it, but a magnaflux will show it up. Are the areas where the seal or seals run worn. You may have to have those areas dealt with so that the seals don't leak excessively. Since we don't turn tractor engines as fast as we do cars or truck engines these factors aren't as absolute as you would believe, but they are still very important. Also be aware that cranks are made out of Cast Nodular iron most of the time, so they are very soft. You can ruin a crankshaft very easily with a sharp tool. They should always be stood up on their flywheel end and kept away from any moisture where they can get surface rust on the journals. Good luck with the engine!!!

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