It's been a fun few days for me. Last week leaving work my idler pulley started making noise and completely gave out, throwing the belt. I replaced the idler and the belt and everything seemed fine. I drove all over town and everything looked and acted just fine. The next morning I left for work and made it a few blocks before it shredded the new belt. I got time to replace the tensioner and throw on yet another new belt today and now the belt is walking off the supercharger pulley by a single rib, toward the outside of the engine, in effect also riding slightly off the idler pulley. The only mods to the drive belt area are a 15 percent reduction SC pulley and an ATI super damper that have been on there for at least six months without issue. I'm usually pretty good at diagnosing issues but this one is driving me insane. If the belt were walking the other direction I would think my SC pulley had come loose and moved a bit, but it's still just as tight as the day I put it on. It's also weird that the walking issue only happened after getting this new belt. There is a little wear on the damper, but it just looks like the paint has worn off on a couple of ribs, and there's no discernible difference between the ribs as far as I can tell. Not having a car is really stressing me out and I'm about to start throwing parts at it.

 

I am certainly no expert - but it appears to me those 3 inner ribs look unusual/worn. I see the paint wear...However...
I also installed a 15% (w/stock damper) and was concerned about alignment and belt walking. It's been near 4 months now and (luckily) no issues.
My apologies for not having a an answer to solving your dilemma.

 

Is the dampener all the way seated? It looks like it maybe out some and that would throw the belt out of alignment.

 

Since this started happening after the new idler pulley was installed, I would check to make sure it’s mounted in the correct hole. There are two holes close to each other and sometimes the bolt for the timing cover is missing making it possible install the pulley in the wrong one.

The clearance between the idler and crank pullies looks tight and maybe belt bouncing/slapping is causing the belt to hit the crank pulley. An idler pulley mounted in the wrong hole and/or a larger crank pulley might make this even tighter. Not sure which ATI you have, but even the “stock” ATI pulley is almost 1% larger than stock.

This thread has some info and pics which might help. Be sure to read all of the posts as there’s some conflicting info in it: https://www.northamericanmotoring.co...er-pulley.html

 

Good eye! I went out and took a closer look at it and noticed that the inside surface of the damper was further out than the idler pulley. Just about the width of a belt rib. I took the impact to it and it didn't take much to put it back in place. No more belt walk! I'll have to grab a new bolt and some fresh loctite just in case.

 

Glad you got it figured out!