When I removed the clutch and measured it, I decided to replace it as most of the parts were worn to minimum tolerances. You can read about how I removed the clutch here:
21 1973 BMW R75/5 Clutch Removal and Inspection
I purchased the new clutch parts from Tom Cutter at Rubber Chicken Racing Garage including:
|21 21 1 250 035||Diaphram Spring (Heavy Duty)|
|21 21 1 251 801||Pressure Plate|
|21 21 1 236 332||Clutch Plate|
|21 21 1 231 666||Compression Ring|
|21 21 1 231 463||Filister Head Cap Screw (6)|
Preparing for Installation
Here is a picture of the old and new clutch parts. The new parts include an updated design for the compression ring and the clutch plate.
The new compression ring does not use the spacers but has thicker sections at the edge.
The new clutch plate has more rivets than the old one.
The parts need to be cleaned before installation and I used brake cleaner. I also use long bolts, M8 x 1.0 x 35, to help assemble the clutch and three 1/4 inch diameter wood dowels, 2 inches long to support the parts until I can get the long bolts threaded. I use Honda 60 Molypaste to lubricate the diaphragm plate where it contacts the face of the flywheel and the tips of the fingers where they contact the pressure plate. I use the metal bar I made to keep the flywheel from moving when I removed the clutch to hold it when I torque the clutch bolts. And, I use a torque wrench on the clutch bolts.
Here’s the junk I removed from the new clutch parts.
Lubricating the Diaphragm Spring
To reduce wear, I put a thin amount of Honda 60 Molypaste on the edge of the diaphragm spring where it touches the face of the flywheel and on the edge of the fingers that contact the back of the pressure plate. I put on Nitrile gloves and I used a flat toothpick and just a little molypaste on it. I cleaned the edge of the diaphragm spring to remove any molypaste that got on the edge.
Mounting the Clutch on the Flywheel
I put the three dowels in every other clutch hole in the flywheel and then placed the diaphragm spring against the face of the flywheel with the fingers facing me.
I removed the gloves and used a clean pair to continue the work. I don’t want to get any of the molypaste on the other clutch parts. I mounted the pressure plate with the hub against the diaphragm fingers and hung it on the dowels.
Then I put the clutch plate in the center of the pressure plate making sure it is facing the correct direction and hung the compression plate on the dowels and secured it with the long bolts so the washer is against the compression plate followed by the nut. I screwed the bolts in finger tight.
I tightened the long bolts tight enough that I could move the clutch plate and center it by eye but not so loose that it would move easily.
Centering the Clutch Plate
I removed the wood dowels. I used the transmission to center the clutch plate. I hung it from the stud on the top right of the engine and then pushed the clutch plate until it lined up with the transmission input shaft. Then I rotated the transmission input shaft just a bit until the splines lined up and I could insert the transmission input shaft into the clutch plate. I added the other transmission bolts and adjusted the transmission so it was as far into the clutch plate splines as it would go. The heads of the long bolts prevent it from going all the way.
I eyeballed the alignment of the transmission with the engine housing so it was centered left to right. Then I used an open ended 13 mm wrench and tightened the nuts on the top two long bolts to secure the clutch plate and then removed the transmission carefully to avoid disturbing it.
I tightened the nuts on the long bolts 1/2 turn rotating around each bolt until the diaphragm spring was compressed enough to thread three of the clutch bolts in the other holes. I tightened the three clutch bolts until they had bottomed and removed the long bolts.
I slide the transmission back into the clutch plate splines to be sure the tabs on either side of the transmission clear the engine case. I was pretty close but not perfect. I used a rubber mallet to tap the transmission on the side with the tab touching the engine case to center the transmission so it can slide into the engine completely.
I threaded in the other three clutch bolts and snugged them up. I hung the metal bar on the top left transmission mounting bolt and put it inside the engine housing and against one of the ribs in the compression plate. The old style compression plate does not have ribs so the bar can contact a clutch bolt to stop the crankshaft from spinning as the clutch bolts are torqued. But the new compression plate ribs are exactly as high as the clutch bolt head, so this doesn’t work. I kept the bar against the rib with one hand while I torqued the bolts with the other to 17 FOOT/pounds. I had to rotate the engine a bit so none of the clutch bolts were obstructed by the bar.
I remounted the transmission on the clutch splines to be sure it was square with the engine and would go all the way back to the engine clutch housing.
When I get the engine in the frame, I’ll put the clutch actuator rod into the transmission and mount it to the engine, but for now, I’m done.
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Genius – using the transmission itself to center the clutch friction plate. Didn’t necessarily want to spring for the clutch alignment tool, and the other method I’d been told of (by a highly thought of airhead guru) is to wrap electrical tape around the clutch rod ’til it fits snugly in the clutch plate, then use a square to line it up. Liking your method SO much better than either of the others. Thanks!
This technique seemed to work just fine. It takes a couple tries to turn the shaft just enough so the splines can engage, and then everything slides together.
Thanks for dropping by.
Actually, I’ve been scanning this trove of /5 resource for awhile now. You’ve got the whole bike laid out pretty well here, I must say a better job of putting it all together than some of the Grand Poobahs of All Things Airhead, who’s wealth of knowledge I respect mightily, but organizational skills – ehh, not so much.
Thanks for sharing this information to all the beemers society. this is a great gem!
I was wondering if you can advice me…my diaphragm has a small play inside the flywheel. this means that it can “play” around 0.8 millimetre in the outside diameter. is this suppose to be like that on purpose, or it is worn?
on other words, when I place it, since there is this gap, should I need to centre it somehow?
The diaphragm spring is not bolted to any part of the clutch assembly. It sits in a recess on top of the flywheel, so it’s free to move a bit. If you see 0.8 mm of movement (1/32 of an inch) I don’t think that indicates any problem.
Thanks for your answer Brook.
I am a bit worried that I have no way to center it, so the engine might be vibrating. I will try and see the results.
I had my Son help me to install the clutch on my 1976/6. I have already changed the engine seals. I didn’t use the wooden dowels and the clutch ass’y was a bit heavy to line up so the extra hands were helpful. Anyway, we have the ass’y in place(not tightened yet)but I found that the friction plates tend to move around a bit even using the centering tool. With the clutch loose on the engine I centered these plates as best I could and then tightened enough to secure them from moving, centering tool still in place. Now I want to tighten everything up. I’m just wondering if the friction plates do tend to move a little and require a slight centering technique using the centering tool prior to tightening the cover plate.
Yes, the friction plates “self center” when the clutch spins. The centering tool helps get the splines on the clutch plate aligned with the splines on the transmission input shaft so you can slide the clutch plate onto the transmission input shaft easily. If you have the transmission connected to the engine, you should be fine. My technique uses the transmission input shaft splines to align the clutch plate so I didn’t need to use the clutch alignment tool. Either way works.
I hope this helps.
Hello Brook. I have another question if you dont mind.
Im continuing work on my R75/5 with a 90/6 engine and /6 gearbox. (Gearbox shimming fix from a questionable shop, rear main seal and minor stuff)
I might just have shot myself in the foot yesterday while cleaning the clutch components with gasoline, only to see I removed the white paint marks from all but the flywheel.
How serious of a problem can it be if the clutch parts are assembled out of order? I can understand its rare to see vibrations in an airhead coming from the clutch.
I see both the flywheel and the last friction plate have balance holes drilled in them, leaving only the first friction plate in question if you ignore the clutch and spring. Ive considered opposing the balance holes in the flywheel and the last friction plate as my only logical option. Am I overthinking this?
Afterthought: I brought the motorcycle home from a bike shop after quarrels and attitude problems. So my starting point was a box of parts, including the clutch, only marked with white paint. No way of knowing if this was the mechanics personal markings, or BMW’s “120 degree” heavy spot marks. I might not even have assembled it correctly even with the white paint marks.
Love the site. Its a great help.
-Greetings from Denmark – Christian Bjørnholdt
Good to hear you are working on getting another airhead on the road. That’s great.
I’d put the clutch back together and not worry. The “balance holes” removed the out of balance condition of the heaviest rotating parts. It won’t matter what orientation they are to each other when you mount the clutch since they are “balanced”.
What can cause clutch vibration is not having it centered on the flywheel. Getting it centered takes patience. Your target is 0,05 mm or 0.002 inches of run out on the face of the clutch backing plate.
I show how I do this here:
TAKE CARE YOUR DIAL INDICATOR DOES NOT CATCH ON ONE OF THE CLUTCH PRESSURE RING BALANCING HOLES. That would ruin the dial indicator.
I hope this helps.