Installed new belt tensioner idler pulley and crank pulley. And its shredding the belt again. Any ideas?

 

When the belt is off does everything spin freely?

 

Locked up a/c compressor or alternator pulley maybe. Even if one of the pulleys is chipped a little it could shred a belt.

 

Ac compressor works and kicks on

 

alternator was replaced about 8k miles ago

 

This is just a thought, but I had an issue with an R50 where the belt kept slipping after I replaced the alternator. I had replaced the alternator with a refurbished unit from Autozone. The pulleys looked the same between the original alternator and the one on the replacement alternator, so I didn't swap them. It took me a long time to realize the pulley was the issue. I ordered a new pulley from ECS Tuning, and never had an issue again. I turned out the pulley on the replacement was not 100% in line with the tensioner and other pulleys, thus putting stress on the belt.

 

I hope it’s just the pulley. That would be a pretty cheap thing to try.

I can’t think of anything else besides the supercharger locking up some and not spinning right. I pray that’s not your issue. That could eat a belt quick. But if the supercharger whine sounds normal when the belt is on and your car isn’t overheating from the water pump not spinning, then that’s hopefully not it.