I dought it is the blade probably the rotor shaft, A new motor is in
order but at the price of parts a new mower your idiot friend owes you.
He wont be your friend now. And you wont loan out your stuff. My
neighbor wanted to borrow my mower I said its broke, He borrowed someone
elses and I heard him hitting rocks for an hour stalling his loaner
mower.

Dave HVac electric motors dont have Crankshafts.