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Old Thu, Nov-07-2019, 02:33:48 PM   #1
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Default Rotrex/AA belt skipping back/forth on SC pulley

first of all, I hope this is the right place to put this. There doesnt seem to be much activity in this F/I section...

In summary, My belt doesnt seem to be lining up correctly with the supercharger pulley.

I recently started having problems with my supercharger belt. It started squealing on startup and then the squealing would go away after about 10 minutes. The squealing was coming from the supercharger pulley area.

I ended up installing a new gates fleetrunner belt. The new belt is the same as the original but slightly longer because the original was short and barely fit over the tensioner at full lock. Once the new belt was installed, it started skipping back/forth on the ribs of the supercharger pulley. If I pull the supercharger forward gently (slightly bending the bracket) it stops skipping. Skipping also stops if I put a wrench on the tensioner and increase tension slightly. Anyone else run into this issue?

possible fixes jumping out to me:

1. Adjust the angled support on the back of the supercharger bracket to push the supercharger forward. not sure this is a good idea because, if I remember correctly, I believe AA instructions say to tighten it as it sits w/o the belt on. I could be wrong there though. I haven't looked at the instructions in a while.

2. Buy a new belt tensioner. I checked the tensioner with a torque wrench and it has about 18 ft/lb of tension where the new belt has it sitting. Could I have stretched the spring in the tensioner by having it at close to max tension? Would someone be able to check the tension of theirs for comparison? If my tensioner is weak, would a new one pull the supercharger forward slightly and cause the grooves to line up better? I remember someone mentioning that before. I also haven't seen any rubber dust that would indicate the belt is slipping.

2005 M3
AA gen 3 kit with new rotrex c38 installed less than a year ago
6 rib belt/pulleys (except 8 rib supercharger pulley) with Gates Fleetrunner belt
belt installed in center grooves of supercharger pulley as instructed
not sure when the tensioner was last replaced

Video of issue:

Any help is appreciated!

Last edited by iturnright; Thu, Nov-07-2019 at 02:37:19 PM.
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Old Thu, Dec-05-2019, 03:25:01 AM   #2
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Default Re: Rotrex/AA belt skipping back/forth on SC pulley

Little bit tough since your blower pulley is 8 rib otherwise I'd say you should straight edge the pulleys. They a new tensioner. They are cheap. I like to have the belt tensioner around the midway swing.
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active autowerke, belt, rotrex, tensioner

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Discussing Rotrex/AA belt skipping back/forth on SC pulley in the Forced Induction (F/I) Forum - Discuss the ever growing F/I options here! at BMW M3 (E30 M3 | E36 M3 | E46 M3 | E92 M3 | F80/X)