1982 Dodge Ram ram wont start

take off the belts and check to make sure all the pulleys spin free. if so then rotate the one at the bottom, the crankshaft pulley, to make sure the engine turns. you cant turn it by hand, so youll need a big breaker bar and socket for the bolt in the middle of the pulley. if that's all good, remove the starter and look at the gear on it and the flexplate(the gear the starter turns). rotate the engine all the way around while someone watches in the hole where the starter was and look forn worn down/broken gear teeth. that's the grinding sound you heard.