I had a number of “freshen up” projects I wanted to do on this one owner, 1975 R75/6 with 106,000 miles. I worked on the bike extensively in 2009-2010 and five years later it’s time to work on some projects I put off then. One of the projects is to remove and inspect the clutch. At 50,000 miles the clutch splines failed due to lack of routine greasing of them by yours truly. I believe the clutch plate with the splines was replaced then but I don’t know if any other clutch parts were replaced back then.
I have taken the bike apart down to the frame for powder coating, so the engine is out of the frame when I remove the clutch. But, you can remove the clutch with the engine in the frame easily.
When I removed the transmission, I removed the clutch activation assembly. This includes the parts shown below.
The clutch is simple consisting of four main parts and a clutch activation mechanism (above). The diagram below from MAX BMW’s on-line parts fiche for the R75/6 shows the four main parts.
Here are the parts I used
|23 21 1 230 440||FELT RING||1|
|23 13 1 232 088||WASHER||1|
|23 13 1 232 079||NEEDLE CAGE – 23X6X2||1|
|23 13 1 232 089||ROD||1|
|21 21 1 234 035||DIAPHRAGM SPRING||1|
|Southland Clutch||Refurbish Clutch|
There are other parts that you will need when you remove the transmission; the four bolts that connect the transmission output shaft to the drive shaft and if you remove the rear drive from the swing arm, the paper gasket between the rear drive and the swing arm.
|26 11 1 242 297||SCREW – M8X1 (from 09/80)||4|
|33 17 2 311 098||GASKET ASBESTOS FREE||1|
There are some special tools that I use. I bought them from Cycle Works. They make removing the clutch and flywheel easy.
To remove the flywheel, I use three M8x1 35 mm hardened (Grade 8) bolts with nuts and washers. These are about twice as long as the clutch bolts.
I also like to use a battery powered impact driver to remove the clutch bolts. You don’t need it, but it removes the bolts without worrying about the clutch rotating.
I previously did this work on a 1973 R75/5 and the procedure is the same for the 1975 R75/6. You can read about the entire procedure here:
Differences Between R75/5 and R75/6 Clutch
On the R75/5, the compression ring design let me fashion a piece of 1″ steel stock to keep the flywheel from rotating as I removed the clutch bolts. The R75/6 compression ring has a different design with ribs that prevent using the bar. That’s why I used the electric impact driver. The R75/5 compression plate is flat so I could measure the thickness, but the ribs on the back of the R75/6 compression plate prevent doing this.
Other on-line resources that discuss this work include:
Remove Swing Arm, Rear Wheel & Transmission
I use the rear wheel to help loosen the four bolts holding the drive shaft to the transmission output shaft. I documented how remove the swing arm here.
Once I get the drive shaft off the transmission output shaft, I remove the rear wheel. Then I remove the rear drive from the swing arm but you don’t have to do this.It’s easier to install the swing arm without the weight of the rear drive. However, if you remove the rear drive you will need to get a new paper gasket that goes between the rear drive and the swing arm.
Now I remove the transmission.
At this point, the clutch compression disk is exposed with the clutch bolts.
I did very similar work on my 1973 R75/5 as noted above. That said, I document below how I did the same work on this 1975 R75/6.
Keep Clutch Parts Aligned
The clutch is simple consisting of four main parts and a clutch actuation mechanism that I’ve already removed when I removed the transmission. The diagram below from MAX BMW’s on-line parts fiche for the R75/6 shows the four main parts.
Remove Compression Ring
The clutch compression ring is secured to the flywheel with six Allen head bolts. These bolts compress the diaphragm spring and it exerts considerable force. Therefore, these six clutch bolts have to be removed so as to slowly relieve the diaphragm spring pressure.
This requires using three high strength bolts longer than the clutch bolts. They are inserted in every other bolt hole. I use a small electric impact driver to remove the clutch bolts. It breaks them loose but the crankshaft doesn’t rotate.
I set the nuts on each of the three long bolts so the washer is at the depth of the threads on a clutch bolt. I have 35 mm long bolts, so the nuts are about half way down the threads from the bolt heads.
I screw in the long bolts until the nut washer contacts the face of the clutch compression ring and then hold hold the bolt so I can snug the nut down.
From here on I try to not stand in front of the clutch until I have removed the clutch compression plate. Should something go wrong, I don’t want to be hit by a flying compression plate.
When all three long bolts are installed, I remove the other three clutch bolts.
I back off the pressure on the clutch diaphragm spring with a socket on a bolt head and use a wrench to back off a nut a 1/4 turn. I move around to each of the three bolts and back off each nut 1/4 turn at a time.
When the nut has reached the head of the bolt, most of the pressure has been released from the clutch diaphragm spring. Now I back off each bolt a turn at a time.
I hold the clutch compression plate so it doesn’t fall off as I remove the bolts. I put a dab of white paint next to a bolt hole on the compression plate and the corresponding hole in the flywheel.
This flywheel was lightened when I raced the bike, so that’s why you see a lot of holes along the edge. Your flywheel won’t have these holes.
When I remove the compression plate, the clutch plate is behind it. As I remove the clutch disk, with one hand, I keep the pressure plate on the flywheel with the other so it doesn’t fall off. Then I put another dab of white paint on the pressure plate hole that aligns with the flywheel hole I marked.
Underneath the clutch pressure plate is the clutch diaphragm spring. I put another dab of white paint on it next to the flywheel hole. I’m not sure this matters but I’d rather be safe than sorry about keeping the clutch parts aligned.
This exposes the flywheel. Again, mine was lightened when I raced the bike, so yours won’t have all these holes in it.
Inspect Pressure Plate, Clutch Plate and Compression Ring
The pressure plate and compression ring are discolored and have grooves in them.
When I inspected the clutch plate, I saw that the side against the pressure plate had worn unevenly. There was no noticeable wear on the inner part of the clutch plate and I could see some of the part number still showing.
The pressure plate and compression ring show signs of scoring and discoloration. When I inspect the clutch plate, it is clear it has not worn evenly against the pressure plate and compression disk. On the pressure plate side of the clutch plate, the part number is still visible at the inner edge of the friction material.
Clearly the pressure plate and compression disk need to be replaced or machined so they are flat and parallel. Also, due to the traces of oil I found on the back of the flywheel when I removed it, and the back of the pressure plate, I suspect the clutch plate is starting to get fouled with oil so it needs to be replaced or relined. I decide to refurbish the pressure plate, clutch disk and compression disk. I send these three clutch parts to Southland Clutch in California for rebuilding. They machine the pressure plate and compression plate so they are flat and build up the clutch plate to make up the difference in thickness. The cost is about 1/2 the cost of new parts.
Inspect Diaphragm Spring
I measured the distance of the fingers on the clutch diaphragm spring from the edge. I use a piece of glass for a flat surface and place the diaphragm on it with the fingers pointing up.
The specifications place the lower limit on the height of the fingers at 18 mm, so this diaphragm’s fingers are collapsed too much so I will replace the diaphram with a new “sport” version, or heavy duty diaphragm spring.
Inspect Clutch Actuation Mechanism
Here are all the clutch actuation parts I removed before I removed the transmission.
As I inspected the parts I could see that the throw out rod was damaged. The rod is discolored from high heat, the end of the rod next to washer has mushroomed and the washer is welded to it.
I find that the roller bearing plate is damaged and bearings are falling out. I think I took this clutch apart none too soon.
Refurbishing Clutch at Southland Clutch
Southland Clutch advertises in the Airmail magazine, the publication of the Airheads Beemer Club. I have read notes on the Micapeak Airheads Forum that are complimentary of their work. I found them knowledgeable about BMW airhead clutches when I spoke to them on the phone. I shipped them my clutch parts (they are in greater Los Angeles, CA) and got the refurbished parts back in my hand 10 days later. I was promised 48 hour turn around after they received it. I got a phone call the day it arrived, another when the work was done. I am completely satisfied with their customer service, BMW airhead knowledge and ability to complete work when they promise to.
I shipped the three clutch parts in a sandwich using tie-wraps through the bolt holes to protect the thin metal edge of the pressure plate from damage during shipment.
Here are the refurbished parts I received from Southland Clutch help together with tie wraps.
The pressure plate and compression ring have been balanced and there is a yellow registration mark on them to ensure they are installed correctly. You can see the holes drilled into the edge of the compression ring used to balance the two parts.
Here are the three refurbished clutch parts. The clutch disk has new friction material with the thickness adjusted to make up for the material removed from the pressure plate and compression ring to make the flat and parallel.
New Clutch Diaphragm Spring
Here is the new “sport” or stronger clutch diaphragm spring I bought with the part number in the middle.
This is what new spring fingers look like.
I measured the finger height at 18.65 mm.
The specifications for the original R75/6 diaphragm spring height is 18.5 – 19.5 mm. But, due to the stiffer spring of the sport version, the spring height is less at 17.0-17.7 mm. It looks like the new sport spring has about 1 mm more finger height than the specifications. I guess that’s better than 1 mm less 🙂
Preparing Clutch Parts for Installation
I put a very faint smear of Moly 60 grease on the tips of the diaphragm fingers using a Q-tip and then use my rubber glove to remove all but a trace of it.
I also put a very light smear on the outside edge of the diaphragm that presses against the pressure plate.
I use brake cleaner to remove oil and debris from the machined surfaces of the pressure plate and compression disk. I keep cleaning them until there is no discoloration on the blue shop towel.
Install Clutch Parts on Flywheel
I use a clean pair of rubber gloves to install the three clutch parts. I don’t want to get any of the Moly 60 grease or grease from my fingers on the cleaned pressure plate, compression disk or clutch disk surfaces.
I use three wood dowels inserted into every other clutch bolt hole on the face of the flywheel to hang the three clutch parts on the flywheel.
I hold the diaphragm on the face of the flywheel with the fingers pointing toward me.
I put together the three clutch parts aligning the pressure plate and the compression ring yellow marks and use a clutch bolt to hold them together temporarily.
Then I insert the sandwich of the three clutch parts on the wooden dowels with the pressure plate against the fingers of the diaphragm spring and remove the clutch bolt. The sandwich of the three parts hangs on the dowels.
I insert the three long clutch removal/installation bolts in the other three holes in the clutch and thread them into the flywheel while holding the clutch parts against the diaphragm spring.
When I have all three long clutch removal/installation bolts threaded into the holes in the flywheel face, I remove the three dowels and I tighten the long bolts a turn at a time while I try to move the splined hub of the clutch plate.
When I can’t move it, I back the bolts off a 1/4 turn so I can just move the clutch plate with my fingers. By eye, I adjust the clutch plate splined hub so it is approximately centered. Then I take the transmission input shaft and insert it into the clutch plate splines. I have to rotate the transmission shaft a bit to get the splines to align.
Then I use the upper right stud in the engine that the transmission mounts on and align the transmission ears so they will fit into the clutch housing without interference. I can’t push the transmission all the way into the clutch housing due to the long bolts but I can get it aligned by eye.
I remove the transmission and tighten the long bolts a turn at a time. As the clutch parts compress against the diaphragm spring, I can start the regular clutch bolts in the other three holes.
When the three regular clutch bolts have been threaded in 3 or 4 full turns, the clutch is compressed enough that the transmission ears will slide inside the engine clutch housing. I install the transmission to be sure it will mate without interference with the clutch housing. The first time I did this, the transmission was a bit our of alignment, so I removed the regular transmission bolts and backed out the long bolts until I could move the clutch plate spline hub again. I inserted the transmission input shaft into the clutch plate splines and adjusted the clutch plate to improve the alignment. When I had the three regular clutch bolts installed 4 full turns I checked the transmission alignment again and the transmission ears smoothly fit inside the clutch housing.
I continued to tighten the three regular clutch bolts until they were snug and then removed the long bolts and installed the other three clutch bolts until they are snug.
Once again, I inserted the transmission again to be sure the transmission ears smoothly slide into the clutch housing.
I insert a wide screwdriver blade in between two teeth of the flywheel and brace it against the left side of the engine to prevent the flywheel from turning when I torque the clutch bolts.
The clutch bolt torque is pretty low at 16 FT/Lbs, and the teeth of the flywheel are strong enough that I won’t break a tooth off the flywheel. I torque the clutch bolts in a cross-wise pattern to 16 FT/Lbs.
This content was originally published here.