Last month I changed the clutch in my '81 R80G/S. The bike only had 20k miles on it. The clutch was in good shape, however I was concerned over rumors I had heard about the old stock clutch in this particular bike. Several sources had told me that the stock clutch in this bike was prone to breaking. I haven't heard a definitive source to say what year the new style clutches are used. However, Ed Culberson's bike (Amigo) which was several years newer than my bike had the old style clutch that broke, and so chances were pretty high that my '81 had the old style. Not to mention, '81 was the first year to have the redesigned light weight clutch assembly. The difference between old and new clutch can be seen between the outer clutch pad material and the splines. The old clutch has eight evenly spaced 1/2" diameter circular holes interspersed with eight 1/4" holes. The new clutch has only six half moon like holes. As Pete Serino pointed out to me, you can stick a mirror in between your tranny and engine next time you do a spline lube to find out what type of clutch you have.
Since my wife and I are planning to take a 2-3 year round the world motorcycle trip on our '81 R80G/S and '92 R100GS this Spring I decided to change this clutch as preventive maintenance. While doing this, I was able to check and service other things that needed replacing such as a new drive shaft booty, replace the clutch fulcrum booty, lube the splines, and do a general check up on many of the bike components.
I've written up a "here's how I changed my clutch". Note that information on the clutch is relevant to '81 and later 2 valve boxers. I wanted to keep track of which tools were used on this project so that I would have a good idea how complete the set of tools I carry around is, should I need to do some major surgery while on the road. In certain steps, other tools may be used rather than the ones I chose.
The order of removal could be rearranged a little... However, this is how I did it this time...
remove luggage system remove seat remove gas tank 11.3 gallon Acerbis tank 13mm socket remove battery 10mm socket + 3" extension remove negative lead first, so that the frame isn't grounded should your wrench accidentally cross when you undo the positive side. 6mm allen 13mm socket had to remove the ohlin shock to remove the battery... problem with G/S... 17mm socket 17mm wrench remove rear wheel 17mm lug wrench hammer 10mm wrench to loosen rear brake rod so as to make it easier to remove wheel. remove air intake cover needle nose pliers remove air filter remove air filter cover retaining clips remove battery holder 10mm socket + extension 10mm wrench remove carburetor & air intake elbow tube standard screw driver 10mm wrench remove starter cover - this step was to simplify removal of breather tube into air box 5mm allen remove lower air box 13mm socket - for two bolts universal joint 3" extension 12mm wrench - for nut drain final drive 19mm wrench - drain plug 17mm wrench - filler plug 14mm crush washer - drain plug 18mm crush washer - filler plug drain drive shaft 17mm wrench 12mm ID crush washer x2 (drain and fill) remove speedo cable & ground cable 10mm wrench open drive shaft booty gear oil spills out... small standard screwdriver needed to loosen clamp. remove the 4 drive shaft bolts put the engine in gear to stop the drive shaft from spinning 12pt 10mm wrench 32oz ballpeen hammer remove rear brake rod and pedal 10mm wrench for rear end of rod 13mm socket 13mm wrench - rear brake pivot axle remove swing arm ground 27mm or 1 1/16" socket wrench extender bar 6mm allen socket loosen clutch booty clamp small standard screw driver remove clutch pivot axle for clutch fulcrum assembly my clutch booty had been damaged and patched up by the previous owner. it was now weakened, and ripped when I removed the the clutch pivot axle. 10mm wrench drain transmission 19mm socket - drain plug 6" extender 14mm crush washer - drain plug remove shifter lever 5mm allen socket 6mm allen socket remove transmission 6mm allen wrench 12oz ballpeen hammer 13mm wrenchThere are four bolts that hold the transmission housing to the engine. Two of these connect through the air box and so have already been loosened. The lower two require a 6mm allen wrench and a 13mm open ended wrench. I also used a small hammer to break the torque. Pull the transmission back until the transmission input spline clears the clutch spline (about an inch). Then rotate the bottom of the transmission up to the left (clockwise) so that the neutral switch can be disconnected. The upper right transmission housing bolt can be used as a pivot for rotating on. This switch may have an insulated grounding, but just in case it didn't I made a note of which terminal the brown and the brown/black connector connected to by marking them with masking tape. Pull the transmission out from the left side.
To remove these screws, I needed to fabricate a tool to hold the clutch/flywheel assembly from turning. I got the idea from figure 3.11a in the Haynes manual. This figure refers to a different clutch design, however the tool was useful here. I cut a flat bar (4-6") and then drilled a hole at each end. In one hole, I put a 8x25mm screw&nut in to use as a peg stop, The other end I attached to the lower left engine/transmission housing bolt with another 8x25mm screw. The three pairs of screw on the cover plate have an indentation to which I inserted the peg stop. With this in place, I could then break the torque of the screws. I first removed one of each of the three pairs. I then turned each of the remaining three bolts at the same time such that pressure from the diaphragm spring would release evenly. Originally I had purchased three 7x30mm screws because a bmw mechanic had left me with the impression that the 7x16mm screws that were in there were not long enough to remove the pressure from the cover/clutch/pressure plate assembly. This turned out not to be the case. The screws come out quite easy with the above fabricated tool to hold the cover plate in place. Once all six screws are removed, the cover plate should come off along with the clutch, pressure plate, and diaphragm spring. There are three alignment pegs centered in between each of the three pairs of screws. One of the pegs stuck and was wedged by the spring, so I had to reinsert the screws to jar the alignment peg.
Both Haynes and Clymer recommend to replace the clutch plate and pressure plate as a pair. Cal BMW recommended that I replace the clutch diaphragm spring as well.
Since this whole operation was preventive maintenance rather than due to a clutch wearing out or breaking, I probably could have skimped on the pressure plate and spring, but I didn't. The old clutch had 20k miles on it and looked about as thick as the new one. The spring looked just like the new with out any visible wear, and the pressure plate looked fine as well. My micrometer reads .196" (outside) - .203" (inside) thickness for the old clutch. I didn't measure the new one before I put it in. As it turned out, my '81 R80G/S did have the old style clutch that is rumored to have a high unexpected failure rate.
As I mentioned earlier, the difference between old and new clutch can be seen between the outer clutch pad material and the splines. The old clutch has eight evenly spaced 1/2" diameter circular holes interspersed with eight 1/4" holes. The new clutch has only six half moon like holes.
Reassembly was fairly simple. Insert clutch diaphragm spring with cone portion facing rear of bike. Insert pressure plate, clutch, and cover plate using the guide pegs to help align. Start the six screws with approximately 3 revolutions. Center the clutch plate before screws are tight. I bought a clutch centering tool for $20 to do this at a bmw mechanics recommendation. It's not clear to me this is needed, since I believe when installing the tranny one should know if the clutch is centered properly by way of the transmission input splines. However, since I haven't done a clutch without this tool, I can't recommend against using it. The tool is basically a solid rod with a tip on the end. The tip fits into the center hole of the diaphragm spring while passing through the clutch like an arbor. Part number is 88 88 6 212 650.
Tighten the six screws at the same time such that pressure is applied evenly. These screws should be torqued to 21Nm according to Haynes. I decided to warm up my torque wrenches since it was about 0 degrees F in my garage before the heater brought the ambient up to about 40F.
Reassembly is pretty much the reverse. Be sure to grease the clutch and transmission input splines. The recommended grease for this is BMW #10 grease which is a red lithium base grease with special anti corrosive additives.
I took the opportunity to clean and repack the bearings in my swing arm. The cover washer for the swing arm was caked with dirt and grease. Further someone had used two different kinds of grease in the swing which I'm leery of after having seen grease react and drastically change characteristics in the past. The tappered swing arm bearings look like the same ones in the front wheel bearings on this '81 R80G/S. The bearings cleaned up well with some WD-40. I repacked with a MoSO2 grease. I have some sodium fiber wheel bearing grease, but opted not to use it since I've never seen this kind used on a beemer. I'd love to see an FAQ someday on the merits of various greases.
Dave Thompson
Champaign IL
'82 R65LS '92 R100GS '81 R80G/S
davet@roadkill.com (http://www.roadkill.com/~davet)