Throwing serpentine belt

[Cooljesus]

Hello, I recently purchased a 2004 tige 22v riders edition with a PCM ZR6 390. We had it out surfing yesterday and the serpentine belt popped off the engine. I couldn’t see any obvious problems. I spun all pulleys by hand and the impeller seemed to have more resistance than I expected so I changed out the impeller (impeller looks perfect and without the pulley installed it spun freely) and put the belt back on. Within 10 seconds the belt flew off again. We limped back to the marina without the serpentine belt installed. Just wondering if anyone else has experienced similar issues and or diagnostic advice for pinpointing the issue?

I’ll be checking pulley alignment with a alignment laser tool tomorrow. My best guess, without any diagnosis, is perhaps the crank pulley which I assume is part of/or bolted to a harmonic balancer that is separating.

Any advice or insight will be greatly appreciated.

[UNSTUCK]

I would guess that if there was no play in any of the pulleys your alignment is fine. I'd look very close at the ribs of the belt and also the ribs/grooves in pulleys. There could be something small stuck in a groove that is causing the belt to jump when they meet. If you decide to throw parts at it, start with a new belt.