We see this all the time at our Marina, on small block Chevys. Two things can cause it. Bolts that aren't torqued tight enough (or are the wrong ones....some use metric, some sae) or a backfire while cranking. There is a lot of force on those bolts while the engine is starting, trying to shove the starter sideways.

Buy brand new bolts, and torque them to the manufacturers specs, which generally is 50 ft lbs.

If the starter had a brace on the backside originally, reinstall it. Some do, some don't. People leave them off when replacing starters to take a shortcut.


Don