Chech the battery terminal voltage while cranking. If a fully-charged battery is dropping below 5 volts while cranking, there's too much drag on the crank, or you've got a shorted armature. Now, remove the starter, and check terminal voltage while doing a no-load run. If voltage is still low, you've got starter problems.
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!