First, check the thrust washer clearance with a feeler gauge. Second, get a light and magnifier to look at all the needles in the bearing. Thrust washer clearance, cracking in the needle bearing cage, damaged needles, sometimes it gets hot and turns the big end of the rod blue, and look for dis-coloration on the journal. If it was the main bearings, there should be up and down play at the rotor or the drive gear(the ends). If that is the case, the crank is probably okay, except for the 50 or so race hour lifetime?