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Keif 06-03-2012 11:46 AM

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 /
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.

Time required:
Took one evening going very slowly and taking lots of pictures.

See pictures, videos, basic steps, descriptions --> here.

Keif 06-03-2012 11:47 AM

Labeling / descriptions on pictures and videos complete. Supercharger working perfectly now.

lendog15 06-24-2012 04:06 PM

I love reading posts like this. Not that I would even ATTEMPT to do something THIS detailed but I guess I'm a sucker for happy endings when it comes to an issue most would chalk up to "NEVER TRYING THIS DIY DEAL..." which is sort of me.

Thanks for posting.


Hossy 07-19-2012 09:46 AM

Very well done, Keif - this just happened to my B7, almost at identical mileage and with the same issues. Fortunately warranty is replacing the entire supercharger, but great to know that a full replacement is not always necessary in the future. Very nice detailed step-by-step pics and vids!

Keif 07-19-2012 01:36 PM

Gracias! =]

fieldydwb 01-13-2014 11:59 AM

Having the same issue.

Keif, where did you order the kit from? I am thinking of doing the same thing.

Is it a difficult process?


dadasaab 04-21-2014 04:18 PM

Hey Keif,

Were you able to figure out why there was oil in the intake of Supercharger?

ados 05-14-2014 08:11 AM

Hey Keif, could you please provide map for this supercharger. We are going to install it to m50 engine and need this for calculation. Thanks in advance.

F-Tar 06-12-2014 12:40 AM


Originally Posted by dadasaab (Post 8292155)
Hey Keif,

Were you able to figure out why there was oil in the intake of Supercharger?

Crankcase ventilation.

Nice description!

Sent from BimmerApp mobile app

SeeYal 06-12-2014 04:34 AM


Originally Posted by Keif (Post 6961242)
Gracias! =]

Keif, glad to hear you sorted this out... Nice work!. No issues on mine yet...:thumbup:

Where are you located in Houston? Let's get together once after work... Bayou City and I go once a while enjoy some refreshments after work at Nextdoor Cafe on Memorial west...

Iwo 09-10-2014 10:11 PM

I have a question regarding the B7. I'm looking in to buying 2008 750i or the 2007/08 B7. I'm curious if the B7 is more challenging to work on then regular 750i ? Is the supercharger prone to failures ? Has the 4.4 in the B7 have tendency to leak like 745s ?
I know it's a little different from regular 4.4 and I know the 4.8 in the 750 is pretty reliable...
I'm not a BMW newbie.. ( on my 7th bimmer now) and I'm mechanically inclined plus I have access to parts so I'm not afraid of 7s :-)
Thank you in advance for any input !!!

ssmokn 10-10-2014 03:58 AM

Well done!

transporter1740 10-13-2014 07:29 PM

4.4 turbo
Google Bentley Arnage

MontanaRob 12-19-2014 10:27 PM

Great write up thanks!

TPIOlds 01-12-2015 09:09 PM

This may be a little off topic.

Is there any one here that would like to sell the old clutch assembly.

Please let me know

MontanaRob 11-30-2015 07:07 PM

FYI time to replace mine. I searched hard and found a complete repair kit for $619 including shipping from BMW of Fairfax VA. They have a special on parts via online order.

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