Starter not engaging
I think maybe toward 67dart273's point, it may be a crappy rebuild...meaning the core they used might just have the mount holes wowed out or some other issue that is not allowing it to engage properly. Do you still have the original one stud, one bolt combo?? This is important because of the shoulder on the stud. Some units even had a sleeve (prolly aftermarket repair) to fix sloppy cases. This means the case could have been drilled previous. Look carefully at the setup for slop. HTH, Lefty71
