Starter wont spin flywheel sometimes

[Terry H.]

I have a '90 J model 6.2. Several months ago the ignition swithch locked in the start position with the engine running. I couldnt kill the engine with the switch, and before I could disconnect the batteries, the switch burned up filling the cab with smoke. I was 2 blocks from a dealer, so they replaced the switch and starter motor for me. two weeks later this problem started. Occasionally when I try to start the engine, the bendix engages (click) but wont turn the flywheel. If I keep trying, eventually it will start ok. I have replaced the starter motor, ran an independent exciter circuit, (wire from battery to push button momentary switch on dash to exciter post on starter) and the problem persists. Is anyone aware of an internal engine problem that may be causing unusual compression or binding that may be causing the engine to semi lock up????? Its odd that eventually the starter does spin the flywheel at the normal speed and will crank right up. I have noticed that by turning the flywheel by rolling and popping the clutch to turn the flywheel just a little, will usually result in the starter working then. Since 2 new starers and new circuit changed nothing I believe the problem is internal and not in the starter / electrical. PS have replaced positive and negative battery cables.
Any ideas greatly appreciated.

[john8662]

I'd suspect something to do with your manual tranny, maybe the clutch isn't disengaging completly. If you have a volt meter/ohm meter handy you might test battery voltage when the starter motor doesn't turn over the engine. That way you can see if the solenoid is getting fire to the starter motor, and if its binding. Because if you see a drastic drop in voltage when engaging and not turning over, its probably binding or somethings locked down.

Another thing it could be possibly is that the starter needs to be shimmed, it might be engaging too tightly and causing it to bind.

[jcomp]

Perhaps you have some damaged teeth on the flywheel.