[Christ]

Well, from rebuilding starter motors, I know that the number one cause of irreparable damage is the "hammer trick", wherein people somehow think it's a good idea to whack the button on the back of the starter with a hammer, even though there's a compressed ferrite powder magnet on the inside of the housing with no cushion against the impact.

That said, you're working with a slightly larger motor, but you're probably better off using a deadblow hammer or a rubber mallet, or at least using a wood dowel to absorb some of the impact shock.