Alternator "pivot" bolt failure

Demonic said
A bent or out of true crank pulley can cause this. The belt gets tightened when the crank pulley is in a "loose' spot, then on every revolution when the belt gets tight, the bolt gets a little tug.

Start it without the alt belt and look at the crank pulley. Or just watch it closely while cranking.

This is interesting. I if I remember correctly, I put a new damper on a few months before the first bolt broke. I should be able to get a dial indicator on and check how true the crank puly is..