American Motors: amc 5.9 v8 starting problem, pep boys, starter motor

Question
hi i have a 78 5.9 v8 jeep, when i turn the ignition to start engine the starter engages the ring gear but tries to grind the teeth off, i checked the starter drive and ring gear for wear and found both showing damage, i replace both ring gear and starter motor turned the ignition key to start the starter engaged again trying to grind away the ring gear, engine turns by hand so not ceased, it seems that the starter is in full cranking mode before it reaches the ring gear and there fore tries to grind away at the ring gear , any thoughts on this.  

Answer
I had this problem once. I replaced tha starter with a generic rebuilt unit from Pep Boys. I later found out that they gave me a Motorcraft starter for a Ford.
Though AMC used Motorcraft starters, the nose of the starter is longer than one used on a Ford.
Try comparing starters down at the parts store, make sure it is for an AMC/Jeep.