I have a Pioneer fra-100 flywheel which is a 168 tooth flywheel. I also bought a new starter with a staggered bolt pattern which is for 168 tooth flywheel. When I put the starter on, I had to shim it to .020" for it to start fine. It did one or two times, then I had to shim it to .060". Same thing with that, then I had to shim it to .100", then .140". Before I kept shimming it each time, it grinded. So why do I have to keep shimming it? What's the problem?

I put half shims on the outboard side.