How do you know if a crank needs to be turned?
 

I am selling my crank and have had a few people ask if it needs to be turned. I don't really know what that means or how I can tell if it needs it. Can someone explain?

Any evidence of wear-scratches etc on the crank or rod journals. Turning is milling these surfaces down, smaller journal diameter, to a correct clearance with bearings for proper oil pressure. Basically a good smooth surface for the bearing surface. You turn the crank down then put larger/thicker bearings in.

Hope that makes sense

what ky said. also you can check the clearances with plastigauge. though i don't know what the specs are for the genIII motors.

What Ky and bluecajun said + using micrometers to actually mic the diameter and compare with factory specs and tolerance. Basically on most late models if it is a smooth surface without scratches that you can really catch a finger nail on you are most likely ok.

if the journals need a little cleaning up, you can use emerycloth to smooth it out fine...