Did my first Autocross of the season today and had a near disaster happen. On the last hairpin of the last run for the day, my serpentine belt jumped off. Fortunately, it did no damage, but I'd like to know why it happened. The car has 17,800 miles on it, and what has changed on the car since last season is: 1.) New EC SC pulley & tune 2.) New PSK from NW's. Other mods are in my sig.
It was fairly hot out (95deg.) and towards the end of the day I was seeing 130-140 deg.'s IAT's and about 204 deg.'s ECT's. I've been running with the new setup for a few months now, but of course haven't pushed it like I did today. After getting the belt back on, drove 2 hours back home (some places fairly aggressively) w/ no problem. The belt seemed pretty snug on the install, and I'm pretty certain Rob gave me the correct belt. Belt stretch? Weak tensioner pulley? What da ya think? It could have taken out many expensive parts today; I was very lucky!

 

next to the pulleys is the coolant reservoir overflow. it should have a small line attached to it. its possible some of the coolant came out and got on the belt causing it to slip off. or the tensioner itself may be weak allowing the belt to come off.
the tensioner has a spring on the backside. it should be centered in the slot on the backside of the tensioner. hard to see but look . if its not centered or close it could be the cause

 

Is it possible that the crank pulley is coming apart. That is, that is is separating from its hub and the pulley has come too far forward putting it out of alignment with the other pulleys?

That could cause a whole lot of damage if it did come off.

 

I am with Steve on this one, some fluid had to have gotten onto the belt. Especially, since it was fine after re-install. Just keep an eye on it... It could be something else, but, running in those conditions, it is possible it puked some fluid.

 

Yes, check this, it happened to someone on here.

 

my son put a psk on my srt last winter, after the installation he noticed the serpentine belt was riding very close to the outer edge of the tensioner pulley with the engine running. in fact it was on the outer rounded edge w some gap.
we had to respace the pulley out, about 1/4" or so more than the orignal spacer, to get the belt away from the outer edge of the pulley.
we cut down a sleeve from the parts drawer.
if your crank isnt coming apart you might want to check the tensioner to belt alignment. young eyes wont need a smart stick.and after you are aware of it you wont either.
i think it was mentioned in a post on this forum but i cant find it right now to reference. maybe it was in the needswings lit.
good luck hope the fix is cheap.

 

Thanks for the replies. The crank pulley looks good, all other pulley alignments look good also. Steve may be right, I noticed a few tell tale drops/stains around reservoir, but very minor. I may have been slightly over full and expanded or sloshed a bit out. It's hard to believe a few drops could throw a belt though. Is there a way to determine if the tensioner is getting weak, other than by feel? Is there a torque level setting that we should be able to achieve before the tensioner pulley starts to overcome the spring strength and start to rotate?

 

Steve, could you please elaborate on this a bit. I just can't see it; maybe w/ a mechanics mirror? Are you saying that if it's past center, that the spring is getting weak?

 

I just don't see this happening on a stock crank pulley. Any pulley failure I have heard of was from an aftermarket crank pulley, not a stock one.

 

http://i291.photobucket.com/albums/l...p/IMG_0819.jpg
Here is a photo from another members thread, of a failed one. It moved forward almost 1/2" but didn't fly off. He totally dodged a bullet w/ that one.

 

My guess would be the tensioner but I don't know. I pumped oil all over my belt and it stayed on. My temps hit 245º and IAT's 180º and my belt stays on. Good luck on your search for the cause.

I had a Code3 before and now a 178 with the PSK.

Les

 

its hard to see but if you look hard enough you can see the slot that the tensioner pivots on. half way is were you want it.

matt my oem crank pulley failed at 30k . elastomer came out halfway around

 

Here is the part and the slot is on the right of the pulley starting at 3 o'clock.