Due to the age of this bike and the oily grunge I found on the compression plate, inside the clutch bell housing and on the top of the shelf under the transmission, I suspect there is oil leaking from the rear crankshaft main seal and/or the oil pump cover o-ring.

That can contaminate the clutch plates and cause the clutch to slip. Since I have to remove the clutch to get the flywheel off so I can access the rear main seal and oil pump, I remove the clutch and inspect it.

NOTE:
I removed my engine from the frame since I am rebuilding this bike. But you can do this work with the engine in the frame.

Parts List

Upon inspection, I find that oil and transmission spline lube are spattered on the diaphragm spring and the compression ring. So I had the clutch refurbished at Southland Clutch. I was very pleased with their service and response when I first used them on my 1975 R75/6. The only part I need to buy is the diaphragm spring (Part# 21 21 1 234 035).

The specifications for the 1977 R100RS diaphragm spring finger height is different than the 1975 R75/6; the R100RS maximum height (17.7 mm) and minimum height (17.1 mm) are less than the R75/6 maximum (19.5 mm) and minimum (18.5 mm). The reason is the spring metal finger is thicker (2.8 mm) on the original R100RS diaphragm spring than the R75/6 spring (2.6 mm).

Mine is still serviceable, but since the diaphragm spring is not that expensive I replace it. That way it’s an entirely new clutch with no need to replace anything again for a long time.

That said, the replacement “heavy duty” spring has a higher finger height than the specifications. It’s better to have more height than too little.

Tools

I use the same tools for the R100RS clutch work as I used on my R75/6. You can find them here.

• 21 BMW 1975 R75/6 Remove, Refurbish, Install Clutch
  • Tools

The Cycle Works clutch extraction bolts and a cordless impact driver make removing the clutch straight forward.

Removing The Transmission

I documented the procedure for my 1975 R75/6. The procedure is the same for the 1977 R100RS.

• 21 BMW 1975 R75/6 Remove, Refurbish, Install Clutch
  • Remove Swing Arm, Rear Wheel & Transmission

NOTE:
You can keep the rear drive on the swing and just remove the swing arm. The swing arm is heavy and harder to install with the rear drive attached, but it’s not very difficult.

Here is what the transmission input spline looks like. It’s rusty but not damaged.

And the clutch plate splines are covered in moly paste which is WRONG.

The paste is applied to the transmission splines NOT the clutch plate. As is evident the paste was put on the outside of the clutch plate spline, never penetrated into the splines and contributed to the crud coating the compression plate and inside of the clutch bell housing.

Remove Clutch

I documented the procedure for my 1975 R75/6 and they are the same for the 1977 R100RS.

• 21 BMW 1975 R75/6 Remove, Refurbish, Install Clutch
  • Remove Clutch

Here are some pictures of the R100RS procedure.

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Inspect Clutch

Here are the clutch parts after removing them.

The diaphragm spring has smears of lubricant across it. This is a combination of moly paste inproperly applied to the clutch plate and oil leaking from the rear main seal and from a flywheel bolt hole that I discovered when I removed the flywheel.

I measured the diaphragm spring finger height and found it on the low end of the acceptable range for the original R100RS spring.

Inspect Refurbished Clutch & Prepare For Installation

I packed up the old clutch compression plate, clutch disk and pressure plate in a sandwich secured with tie wraps in all six holes. I packed it in box with bubble wrap and peanuts to avoid damaging the delicate pressure plate. In about 10 days, I received the refurbished clutch packed the same way to avoid damage.

I believe Southland balances the parts so before I remove the tie wraps I made a registration mark on the compression plate and the pressure plate.

Here are the refurbished clutch parts.

I cleaned the new diaphragm spring with brake cleaner to remove any oil or crud. It was a bit dirty.

I use a que tip to put a trace of Moly 60 paste on the top of the diaphragm spring fingers and in a very light smear on the back of the diaphragm plate where it contacts the flywheel. As the spring compresses and releases these contact areas wear and a small bit of lubrication will extend the life of the spring. I want the moly 60 to be very light so it won’t come off and contaminate the clutch plate.

Install Clutch

The installation is the same procedure for the R100RS as for my R75/6.  You can read how I installed the clutch here.

• 21 BMW 1975 R75/6 Remove, Refurbish, Install Clutch
  • Install Clutch Parts on Flywheel

Clutch Installation Video

I made a short video of how I install the clutch so you can see the procedure in real time.

Minimize Clutch Run-out

After I assembled the clutch, I learned that the clutch bolts do not guarantee that the clutch pack will be centered on the crankshaft. This contributes to unnecessary engine vibration.

I have a dial gauge that attaches to a goose neck attached to a pair of vice grips. I clamp them to the tube the rear engine stud goes through, put the end on the edge of the clutch compression ring. I rotate the engine using the compression plate and watch the dial indicator. At one of the needle extremes, I adjust the dial to set the zero on the needle. Then I put a Sharpe mark on the edge of the opposite edge of the compression plate.  This helps me know which direction I need to move the clutch pack to get it centered on the crankshaft.

NOTE:
The compression ring is close to the flywheel, so be sure the tip of the dial gauge is on it and not the flywheel or you will not measure the run out of the clutch pack, but the flywheel and it’s run-out will likely be about zero.

It shows about 0.025″ of run-out which is quite a lot. So I need to adjust the clutch pack so it’s centered.

DANGER:
I have to loosen the clutch bolts to get the clutch pack centered. BUT, there is considerable spring pressure from the diaphragm spring on the compression plate. Be careful and don’t loosen the bolts too far or the spring can suddenly decompress and damage the screw threads and/or you. Go slow and stop loosening when the clutch bolts are still a bit snug against the compression plate.

I loosen the clutch bolts carefully until they are just snug on the clutch compression plate. The way my dial moves when it shows run-out means the zero mark I set is where the pack is closest to the crankshaft.  You may end up with the zero being at the point the clutch pack is farthest from the crankshaft. If so, then rotate your engine until the sharpe mark is under the dial indicator tip as that will be the point where your clutch pack is closest to the crankshaft.

When I’m at the zero point on the dial indicator I use a piece of wood and place it against the inside edge of the compression plate next to the tip of the dial indicator and hit it with a mallet to move the clutch pack away from the crankshaft. It takes several tries to get the pack centered. I stop adjusting when the maximum run-out is 0.002″.

I’ll wait to snug up the clutch bolts to 16 FT-Lbs until I can use the transmission to center the clutch disk and ensure the transmission will fit in the bell housing of the engine without any interference.

Revisions

2017-05-11 Added section on minimizing clutch run out.