This page covers the removal of the clutch and inspection after the transmission has been removed. Refer to following page and sections for details on how I removed the transmission:
02 BMW R75/5 General Tear Down
– Remove Rear Wheel, Fender and Sub-frame
– Remove Rear Drive
– Remove Swing Arm
– Remove Transmission
When I measured the clutch parts (see below), I decided that they were worn enough to replace the entire clutch. The clutch replacement with new parts will be covered in a separate web page when I complete that work.
I had previously removed the engine so I could powder coat the frame. I had placed it on a cradle using my Park-n-Move dolly when I got it out of the frame.
I needed a way to work on the engine without it moving around and used my motorcycle lift from Harbour Freight for that purpose. The engine is light enough to lift by myself as I had removed the heads, cylinders, pistons, air box and starter motor covers. I lowered the lift as low as it would go, placed some 2×4 across the lift arms and then picked the engine up using my legs to lift it and placed it on the lift. I strapped it down across the lift arms to secure it and then raised it to a comfortable height to work on from my shop stool.
Blocking The Crankshaft
As documented in many write-ups, if the flywheel is removed, the crankshaft is free to move forward and can easily be knocked off the thrust washers.
If you are only removing the clutch, and you are not removing the flywheel, you don’t have to block the crankshaft. Details on how I blocked the crankshaft are in the “11 BMW R75/5 Remove & Replace Flywheel, Replace Rear Main Seal, Oil Pump Cover & O-Ring” web page.
Making a Clutch Locking Bar
I used a piece of 1 inch mild steel bar stock to make a bar to block the rotation of the clutch so I can remove the bolts around the perimeter without the clutch spinning. I drilled a 3/8 hole at one end so it can slide over the transmission stud on the top, right side of the engine. I modified this same bar later to hold the flywheel stationary so I can remove the flywheel bolts.
I cut the bar stock to length so it would just reach the inside of the engine housing and rest next to a clutch bolt and on the inside of the engine housing. I ground the corners off the cut edge so the edge of the bar wouldn’t gouge the engine housing. Then I mounted the bar so it was between one of the bolts at the circumference of the clutch and the engine housing.
Removing the Clutch Assembly
–> The clutch is under great pressure from the clutch diaphragm spring
–> ONLY REMOVE EVERY OTHER BOLT.
–> DO NOT STAND IN FRONT OF THE CLUTCH ASSEMBLY.
Be safe and work carefully.
By removing every other bolt, the remaining three bolts are sufficient to keep the clutch assembly together against the pressure of the diaphragm spring. After I removed the three bolts, I used three 8mm x 1 bolts that are longer than the original ones with washers and nuts. I purchased these at my local Ace Hardware. I set the nuts so the exposed thread is about the same as the thread length of the original bolts. Then I threaded the three longer bolts into the three empty holes until the washer touched the clutch housing and I tighten the nut with a box wrench to secure the bolt.
I removed the remaining three original bolts. At this point the three longer bolts are holding the clutch together. I backed the longer bolts out about 1/2 turn at a time going around to each bolt in turn. The idea is to release the diaphragm spring pressure slowly and evenly.
–> KEEP TO THE SIDE OF THE ENGINE WHILE DOING THIS TO AVOID INJURY
Despite my care, one bolt came loose sooner than the others and the clutch assembly jumped outward on one side with a loud BANG. I cleaned out my underwear and continued to loosen the other two bolts. 🙂
The clutch assembly comes out with the clutch compression ring (5) facing you and the clutch pressure plate (2) behind it with the clutch plate (3) sandwiched between them. The diaphragm spring (1) is last as it presses on the back of the clutch pressure plate. In between the clutch compression ring and clutch pressure plate are spacers (4) each clutch bolt goes through. You can see one of them in this picture.
I marked the clutch pressure ring and pressure plate so I can assembly them in the same orientation if I decide that the parts weren’t too worn.
Here is a picture of how the parts go together but without the spacers: at the bottom is the clutch pressure ring that faces you and at the top is the clutch diaphragm spring that is against the flywheel.
Measuring Clutch Parts and Inspection
I took measurements of the clutch parts and used the information I found at Duane Ausherman’s site to decide the condition of the parts.
Clutch Diaphrapm Spring Condition
Here are pictures of the clutch diaphragm spring showing the condition of the fingers.
One edge of the fingers show wear. I judged them still usable (not badly worn, but certainly worn) based on pictures I found at Duane Ausherman’s site which I have reproduced below.
I measured the finger height above the bench top at 18 mm. Duane indicates that original height is 17.7 mm so mine hasn’t compressed.
Clutch Plate Condition
I measured the clutch plate thickness at the outside diameter at 0.202 inches and at the inside diameter at 0.190 inches. Duane indicates that original thickness is 0.240 inches and he has seen them still working at 0.200 inches. Mine is about worn out.
Clutch Compression Ring Condition
The clutch compressing ring I have looks like the /2 ring shown in Duane’s article
Note: Duane refers to this as the clutch backing plate and Max BMW parts fiche calls this the compression ring, which is the term I am using.
I measured the thickness as 0.218 inches at the at the inside diameter. Duane indicates the original thickness is 0.234 inches, but mine measured 0.227 inches at the unworn part. He doesn’t indicate what the minimum value is but does show some “worn” values for this plate: outer edger at 0.229 inches; inner edge at 0.225 inches. Mine is less than these and combined with the clutch plate being thin, it wouldn’t be long before the clutch starts slipping.
Clutch Pressure Plate Condition
Duane indicates it should be 0.417 inches for the /5 plate. He indicates that deep grooves are “bad” and I take that to mean deep grooves where the diaphragm spring fingers press on the back of the pressure plate. I definitely have pronounced grooves.
Keep or Replace the Clutch?
I decided to replace the entire clutch assembly; clutch diaphragm spring, clutch pressure plate, clutch plate, clutch compression ring and clutch bolts. I ordered the following parts from Tom Cutter at Rubber Chicken Racing.
|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)|
Pingback: 1973 R75/5 Rebuild: Clutch Removal and Inspection | Motorcycles & Other Musings
Do these parts apply to a 1976 R75/6?
Yes, I believe the /6 clutch design is the pretty much same as the /5.
You can check MAX BMW on-line parts fiche for /5 and /6 parts. IF the numbers match, so do the parts.
/5 fiche: http://www.maxbmwmotorcycles.com/fiche/DiagramsMain.aspx?vid=51885&rnd=04282014
/6 fiche: http://www.maxbmwmotorcycles.com/fiche/DiagramsMain.aspx?vid=51887&rnd=04282014
There is one part, (21 21 0 070 51 SPACER) that shows up for the /5 that doesn’t show for the /6. It is used with the /5 compression ring which I think is NLA from BMW. If you replace the compression ring (21 21 1 231 666), then this part is not used any longer due to the design of newer compression ring.
In fact, Rusty in the MAX parts department is very knowledgeable and always a valuable source of parts interchange knowledge between models.
I hope this helps.
very nice presentation! OK, I have a crazy idea and I need help. Want to install a R75/6 motor to a Citron CV transmission. BMW (push pin) type clutch will not work BUT it appears that I might be able to modify the BMW flywheel to take the (throw-out) Citron clutch.
Any thoughts or am I just nuts!
Well, no, I have no idea how to get the French and Germans to coexist in an intimate way 🙂
Best of luck.
First of all, I want to say thanks. Your site has been enormously helpful with my own ongoing ’72 R75/5 restoration. Great pictures, easy to understand text, I really appreciate all the work you’ve put into this, and I always read your stuff before I do any work on the bike.
Secondly, when I was pulling my own clutch, I experienced the same loud “BANG” when loosening the bolts. I realized later (after I’d finished) that I was doing it incorrectly. It’s the inner nuts that need to be gradually loosened, not the outer bolts. That way, the bolt threads, under pressure from the clutch spring, never disengage suddenly from the housing — no bang, no damage to the threads, and the clutch spring slowly releases without causing Dirty Underwear Syndrome.
Again, thanks for all your help. This is a big job, and you’ve made it a lot easier!
Well, your explanation makes sense. BTW, I have a number of “underwear trophies” from my DUS experiences, so welcome to the club 🙂
Add, thanks for the kind words. I’m glad this material helped you and you helped me by explaining where the load BANG came from.
Brook, it appears you replaces your transmission studs with stainless ones?
Any precautions besides double nut and twist them out?
Thanks for stopping by and looking at the site. I did not replace any of the transmission studs or fasteners. The studs were secure so I didn’t disturb them.
Thank you so much for your information Brook. It has made working on my /5 such a pleasure. Wonderful pictures, with easy to read details.
I’m pleased my write-ups have been helpful to you. Best of success on the /5 work.
When you replaced all the clutch components did they come balanced (with marks to line up) or does balancing not have to be done with new parts ?
IIRC, the new parts are balanced and have marks.
Be safe during these tough times.
Thanks much for your detailed explanations. When I did the clutch plate removal on my 1975 R75/6 this week, the three long bolts were threaded in to the bottom of the hole then backed off a few turns. The nuts were brought down to the plate surface then the three remaining short bolts removed. Holding the bolt heads with one wrench, the nuts were then backed off slowly with another wrench. No Dirty Underwear Syndrome as the bolts stay inserted until the spring plate is entirely released.