I've got an 05 Yamaha big bear 400 and have been having issues with the electric start just spinning freely. I took the starter out to try to swap it and saw that half of all the gears were ground down. Went a little further and saw that the idler gear had a tooth that was missing. The PO said it didn't have any issues till he put the new starter on and then a week later it started acting up. Could a cheap starter cause the idler gear to break or could it be something else

Picture of the old starter teeth compared to the new OEM starter


Broken idler gear