Starter grinding
 

Hello This is my first tome posting.
I have all of a sudden gotten starter problems. I had sheared off a bolt awhile ago. No bracket. Installed the bracket. Then several weeks later Starter sheared off bolt in the bracket and block. I tapped and redid the threads. Was fine for quite awhile then suddenly it started grinding. Have been trying to put shims in a bunch of different ways and it still wont mesh. Fly wheel appears fine and its a new starter not rebuilt. Any ideas would be much appreciated!!!