Just last year I put a used tilton starter that I hadn't used for a couple of years, and when I installed it, it would do the same thing regardless of how I shimmed it. What was happening is when it kicked out and turned the engine over, it wouldn't retract as though it was stuck in the flywheel, but it wasn't actually stuck. When I took it out of the car and tested it with a battery and cables, it would kick out and stay that way until I pushed it back in. I went and bought a new starter and problem solved. Now, if you're using a new starter, then disregard. fyi..........