I remember this happened to Moregrip a while back.... It happened to me today, too. The last post on Grip's thread was by Big Tex and is quoted here...

I saw this on my set up and didn't worry about it. Well today it tossed and ripped the belt so i was forced to look harder at the situation under the hood. The problem looked exactly as Tex described it. The stationary idler pulley below the snout pulley looked to be set too far out from the backing plate/mount. Because of this, the belt rides up against the inner lip of the pulley and that can cause a problem on some vehicles if the tolerance is too close as ours apparently were.

What I believe happened was that when I crested a hill the supercharger went from 5 psi boost to vacuum and this may have shocked the tensioner causing the belt to be able to get tossed off based on the above existing condition.

The fix... it always looked like my belt was a little on the long side so I bought a new belt 30mm shorter (a 6PK2830 is 2830 long) whereas the stock was a 6PK2845 (2860 long). The new belt has the tensioner located almost exact center of it's operating range. That should work very well. But it still didn't fix the belt hitting the inside pulley lip described above. To fix that we first took it off and looked at the pulley and mounting spacer. The spacer is a nice "shoulder style that fully supports the idler bearing race. The problem is that the spacer portion (that offsets it from the mount plate) was too thick. So we took it to a local machine shop and had a 10th of an inch shaved off. This put the belt almost perfectly centered on the idler so it can't happen again.

We did run into a small issue after getting the spacer cut down. Directly below the pulley is a mounting boss that can rub the pulley since it is sitting closer now. The fix for that is to file the boss a little to allow clearance for a free spining pulley.

Now it is perfect and should not happen again. I still love the kit!

 

good info! thanks

 

It only cost me $15 (not including the $30 belt) and about 1 hour to get it all working good.

 

Very informative post. I was looking at that again last night when I was changing my pulley. The belt does sit right up against that pulley shoulder. I'm interested in modifying it similar to what you did. I'm sure my belt will end up breaking at some point.

I already needed to go with a shorter belt. My truck has a mild lope at idle. With the stock belt, every good lope would cause the tensioner to tighten up, the belt would get slack on the other side, then snap back and cause the compressor rotors to knock. The tighter belt helped some. Idle tuning helped out more.

 

Thank you for the first post you made. When I read it, I knew we were seeing the exact same thing! That's why I brought your quote over to the new thread.