I mentioned to one of my mechanics my interest in a 312 crank that had the rod journals turned .040", and could tell by his concerned expression that he would have taken a pass. I had assumed that since bearings were available in that size, it must be OK. What IS the practical turn limit? Does a large cut risk more machining error? Is the crank surface-hardened and thus will score more readily? Is there a problem with thicker bearings? What's the story?

6 VOLTS/POS. GRD. NW INDIANA