What was found
(CAN) WHILE BIRD TOWING WITH STC SH04-57 INSTALLED, THE GEN WENT OFF LINE. THERE WERE REPORTS OF A BURNING ODOR IN THE CABIN, FOLLOWED SHORTLY BY THE GEN FAIL WARNING. THE PILOT MADE AN UNSCHEDULED, UNHURRIED LANDING. DISCOVERED THE STARTER GEN HAD TWO BURNED, ERODED & DISINTEGRATING BRUSHED & A COMMUTATOR IN POOR SHAPE. THE STARTER WAS REPLACED, THE ACFT BEHAVED NORMALLY & WAS RETURNED TO SERVICE. THE STARTER WAS SENT FOR INVESTIGATION & OVERHAUL.