hi all . recently i built a 350 SBC and installed it on a run in stand . the problem i'm having is the starter wont disengage off the fly wheel . it doesnt do it every time and i've tried 3 different starters , same thing with all 3. i've also shimmed the starter thinking the gap was too tight , i shimmed it so far that the teeth dont make full contact on the flywheel and makes a god awful sound , even shimmed that far out ,the gear still doesnt retract back in the starter. any thoughts ??