One of the things all the pros do is to check all parts before assembly..good tip for all racers..my life long round track driver, “ Krash” had a real head scratching problem. The starter he ran for years was now not turning over the engine. It was hanging up at the same point of rotation. We first thought because he stored the engine over the winter letting it rest on the oil pan and “ flywheel” ( actually the torque plate from an automatic transmission ) thinking was be may have bumped into the engine and warped the flex plate. ( stock car class with restricted rules do not address this area in the rules...OPPORTUNITY --- so the hot set up is to run a 5 1/4 inch dual clutch disc package on this ring to cut down rotating weight). well when we disassembled the whole thing we found the flex plate was perfect over 180 degrees..but..the other 180 degrees was about .100” under cut. This was a manufacturing error when the teeth were being machined. So t he starter engaged the teeth on the starter ring up until the teeth were wore to the pint that the starter could not engage that half of the ring. We never would have found it unless we compared a few of the other production flex plates. You could feel the perfect alignment over half the diameter but it dramatically dropped off the other half..Let that be a lesson to you..there are manufacturing defects and check, CHECK and Re check..