You've got an internal short in the starter, or something's locking the crankshaft up enough to stall the starter down. Is the positive cable from the battery to the starter routed properly? If it's shorting out against something, you should be seeing some sparks, not just heat buildup. I'd suggest pulling the starter, and trying to run it on the bench with a hot battery and some jumper cables.
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!