Help...trying to diagnose belt snapping issue. Earlier had problems with excessive belt slippage and changed belt and increased belt rap on vortec head unit. Snapped 2 belts in 2 weeks. Head unit has over 60k miles on it and spends freely by hand with no leaks or rattles or excessive play. I don't see an alignment issue or other pulley problems. BOV seams to be working normal. Am I getting excessive blower load under WOT due to mileage on blower? Time for a rebuild? Towing is getting expensive!

 

Check alignment with laser alignment tool. Also check all pullies to include idler pullies to make sure they rotate freely.

 

Check pulley alignment and also make sure the tensioner isnt binding or hitting anything under load. Also make sure the belt isnt rubbing on anything and no, you wont get "excessive blower load" due to mileage. Just make sure the blower spins freely without the belt and that its not binding or getting held up.

 

If alignment is a issue there should be belt fraying on an outer edge

 

When I put the last belt on, I checked all the other pulleys and spun them by hand. No binding or excessive play. I can easily spin the blower. I put over 100 miles on that new belt and no edge fraying was occurring. Just snaps under WOT. I have Superdamper balancer installed years ago. Thanks for the comments.

 

What does the belt look like after it has snapped off? Any fray around the edges?

I'd do what everyone else has suggested - laser alignment. Dayco makes an affordable tool.
Also check that nothing is binding or twisting under load. I had a procharger bracket where everything was laser aligned and properly torqued, but under load the tensioner arm would twist ever so slightly, snapping my belt under WOT. Replaced with an A&A bracket and no problems since.

 

jmule, Indeed serpentine and/or cog belt drives are the Achilles heel of centrifugal superchargers. When everything is right, they are good to go... but it doesn't take much to cause headaches. Looks like you've covered a lot of the bases already. A couple of additional thoughts come to mind that I might share.

1. Make sure all the grooves of all the pulleys are clean and free of debris. Sometimes belt slippage will pack melted rubber in some of the grooves causing severe vibration that will snap a belt under full load.
2. The pulleys may spin freely... but are the bearings smooth? Is there any play in any of the bearings? At 60K miles, I would be tempted to freshen up the bearings in the idler pulleys and blower so they spin free and precise. I also want to make sure there is no deflection of the blower pulley due to tired bearings.
3. Make sure none of your blower or idler bracketry is flexing under load.
4. Are you using a spring tensioner and is it positioned mid way of its travel following installation of the belt? If the belt is too short, then the tensioner and belt will bind. It will not be able to react to the loading and unloading as you accelerate and decelerate causing it to snap.

All the best of luck to you bud. I've got a 50MM cog drive on an F1 with ATI pulleys. Fortunately I've only lost 1 belt during the past 2 years. That was because my transmission decided not to shift causing me to hit the rev limiter a few too many times. I have a brand new F2 to go on the car now, but I cringe at the thought of the additional load on the belt. I'm looking hard at installing a crank drive on it if I can resolve the rack/pinion issue. It never ends....

 

Thanks for all the good information! Come to find out the 35mm blow off valve was starting fail and not opening correctly. I replaced it with a new 50mm value and no problems so far.

 

I would have said check your alignment as well. Nice catch on the bov.