06-03-2012, 12:46 PM
Location: Houston, TX
Join Date: Mar 2008
Mein Auto: 2007 Alpina B7
Alpina B7 supercharger chirping/pulley wobble - clutch/bearings
Car: 2007 Alpina B7 / 70k miles
Relevant history: Centrifugal clutch on supercharger replaced around 26k miles several years ago.
Since I bought car a week ago there has been a metal-on-metal chirping. It has gotten more frequent with each day, then a few mornings ago it sounded HORRIBLE, like an index card in your bicycle spokes. I pulled off a small cover and saw the supercharger pulley wobbling in time with the chirps and clangs.
So, I started pulling it apart. Pictures and descriptions are in the link below, but I'll describe a little bit here, too.
Normal centrifugal clutch operation: (a more comprehensive training document on the Alpina B7 can be found on BMWTIS.com / BmwTechInfo.com)
The belt-driven pulley is bound to the inside portion of the supercharger's clutching mechanism, which can be best described as drum brakes where the outside belt-driven pulley acts like an axle or wheel, which normally spins freely. Once the pulley spins up to about 1,100 rpm, the centrifugal force begins to push the clutch shoes out against the "drum", beginning to lock them together. This inner "drum" is what actually spins the supercharger.
Problems that I've seen so far:
In my pictures you can see that while the centrifugal clutch shoes have plenty of life left on them, a ball bearing and spring have come out of place. These normally help keep proper spacing between the metal pulleys, plates, and clutching components. In addition, there is an inner bearing or spacer that the pulley and clutch assembly rotate on. This bearing was fairly stiff when attempting to wiggle at any angle but one. The bearing wiggle at this one sloppy angle definitely caused the scoring seen in the various pulleys and plates.
Resolution / fix:
I ordered some sort of unlisted supercharger / radial compressor clutch rebuild kit from a local dealer, part number 11-6-57-973-081, for around $952 after taxes. They did not have any diagrams for this, so they could not confirm that it had the parts I needed, but they believed this to be what I needed and got the part number from the supercharger clutch recall repair previously done at 26k miles. I will post more pictures and info about this once the kit comes in.
Kit came in and DID include all parts needed. Used gear-puller tool included in kit to pull clutch/bearing off and press the new assembly back on...process was fairly smooth.
Took one evening going very slowly and taking lots of pictures.
See pictures, videos, basic steps, descriptions --> here.
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Last edited by Keif; 06-09-2012 at 04:20 PM.