R & R'd the a/c compressor clutch this afternoon . . .
The a/c clutch was screaching badly whenever it would engage above 2000 rpm. The gap was way over 0.080" where it's supposed to be 0.013-0.020". It's a Seiko-Seiki rotary R-12 compressor & from what I gather, most BMW compressors are either Bosch or Nippon Denso. All other aspects of the system are working great. Clutches for these puppies are scarce & expensive, the cheapest I found was $277, dealer gets more than $400 for them (just the clutch alone!)
They come apart easily, turn the ignition on & a/c on to lock the clutch & remove the center allen head screw, the fanbelt keeps the pulley from turning. Turn the key off & & take the belt off & wiggle the front plate off of the splined shaft. There is a large snap ring that keeps the pulley on at the center bearing. I had to modify a gear puller to get the pulley/bearing to pry off of the compressor nose, even after wetting it with P.B. Blaster.
I didn't have to take it apart any further, the electro magnet stays put on the compressor. Once off, I chucked the pulley in the lathe & indicated the run out of the friction face within +/- .0005" & took a 0.005" skim-cut off the main friction surface. There were ridges ~0.040-0.050" higher than that from the flux escapement grooves in the front plate. The pulley's clutch friction surface is mild carbon steel and machines easily. The front plate friction surface is hardened but didn't show any appreciable wear & cleaned up nicely with a jitterbug. It only had one 0.040" shim in it so put it back together without it but then the gap was only ~.005" so machined a 0.010" shim for it from shim stock & that put the gap right at 0.016" so I called it good.
Back together & engages sweet with a subtle "click" at 3500 rpm. Fixed the intermittant blower motor (sword) earlier this week, had the R-12 recharged last Spring, so should be set for several more seasons (fingers crossed).
