I modified my 1976 R90/6 a couple of years ago:
Siebenrock 1000cc, Dellorto 38mm carbs, Ted Porter dual plug heads, R90S drilled air box, OSHMO lightened flywheel, tall gearing (32/11 rear drive, rebuilt transmission by Boxer 2 valve with tall 5th gear). Â It revs up much quicker and pulls stronger than stock but in 6000 miles I gone through 2 new clutches, one stock BMW and the other from Southland clutch. Anyone have any experience with the Siebenrock oil resistant clutch? Â Anyone know of any other set up with more friction? What kind of clutch do sidecar racers use?
Curtis #2811
When you say you replaced the clutch, do you mean the friction disc and the diaphragm spring ?
Owning an old Airhead is easy.
Keeping an old Airhead running great is the true test.
Yup. The first time around I bought the whole kit from Bob’s.  Friction plate, pressure plate, heavy duty spring, etc. Powered through it in 4000 miles. Second time I sent it to Southland Clutch.  They machined it and bonded their own friction materials. Lasted 2000 miles.  I might call San Jose BMW and see what they used on their race bike.
Assuming that oil seals on the engine and gearbox are oil-tight and you are not actually fighting an oil-on-the-friction-plate issue, then that would be my advice.Â
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Owning an old Airhead is easy.
Keeping an old Airhead running great is the true test.
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