i use left hand drill bits. they drill in with the drill in reverse. you drill in one size, the go up one size, it grabs and screws it right out.
the harbor freight one's work ok as long as you drill straight and carefully.
it's only a common problem if your motor's not mounted properly. happens to people who think rubber mounts work.
overtightening, crooked mounts, and cheap hardware will break sooner or later.
i use grade 5.8 metric allen head cap bolts in all my bikes, and never broke one. only time i've snapped a stud was from stock hardware, or when my chain snapped and broke the case.