Not sure if I'm in the right place, but I have a 454 in my '67 that is giving me starter problems. It started grinding when I started it. I put in a shim and everything worked fine - for 6 or 7 starts. Then it started grinding bad again. I took out the shim and the same thing. Worked fine for a few starts, then back to grinding. I put in a thinner shim with the same results. Also changed the starter, but you guessed it: same ol' thing. Anyone have any ideas? Is this common for a big block (this is my first foray into the big block world)?

My truck: She may not be the prettiest girl at the dance, but she's all mine!