Can you glue magnets back on a flywheel without having them come off and causing catastrophic failer?

 

Personally, I wouldn't risk it. The makers obviously thought they could stick 'em on, but by the number of failed Suzuki Eiger/400 KQ flywheels, they (or their suppliers) couldn't. I have tried it on starter motors, and it seemed to work, but that doesn't do damage that results in an alternator case full of mangled stator windings and magnetic shrapnel.

 

I've done it on outboard engine flywheels with no issues. You need to clean and scuff the area well, use a high-temp epoxy paste, and make sure you have them in the exact right spot.

Because of so many magnet failures, Evinrude used to make a magnet attachment kit that was really cheap for anyone who had these issues. If you do it right, they won't come back off, at least none of the ones I've done over the years has. One of them is a neighbor, and that has to be 10+ years ago, and he's still cruising along with no issues.

You might want to check Ebay or Craigslist or FB marketplace to see if you can just find a flywheel if you aren't confident.