In order to replace the rear main seal, oil pump cover o-ring and flywheel o-ring, I remove the transmission, clutch, flywheel, oil pump cover and rear main seal.  You can see how I do that here:

• 23 BMW 1983 R100RS Remove Transmission
• 21 BMW 1983 R100RS Remove Clutch
• 11 BMW 1983 R100RS Remove Flywheel & Rear Main Seal
• 11 BMW 1983 R100RS Remove & Inspect Oil Pump

Tools

I use the Cycle Works rear main seal removal/installation tool to install the rear main seal.

NOTE:
I don’t use the two sharp sheet metal screws show at the left in the picture below. They are only used for removing the seal. I use all five of the flywheel bolts, two of which are shown at the right in the picture below.

Parts

This is a list of the parts I used. I bought an engine gasket kit from Euro MotoElectrics that includes the oil pump cover o-ring and the flywheel hub o-ring and the rear main seal. I show the part numbers for them below along with the EME part number of the engine gasket kit. If you don’t buy the gasket kit, you need to order the individual o-rings and rear main seal.

Part #	Description	Qty
GSK-EngineKit422	Engine Gasket Kit, Euro MotoElectrics	1
11 41 1 335 194	ROTOR INNER (from 09/78), Oil Pump	1
11 41 1 253 293	ROTOR,OUTER, Oil Pump	1
11 41 1 338 544	OIL PUMP COVER (from 09/80)	1
11 41 1 335 895	O-RING, Pump Cover (In EME Gasket Kit)	1
11 22 1 337 093	GASKET RING – 59X3MM (from 09/78), Flywheel Hub (In EME Gasket Kit)	1
11 11 1 338 342	SHAFT SEAL – 100X80X10, Rear Main Seal (In EME Gasket Kit)	1
11 22 1 262 060	M11 BOLT, COARSE, Flywheel	5

I decided to replace my oil pump parts due to wear I found when I inspected it. You can see how I did the inspection here:

• 11 BMW 1983 R100RS Remove & Inspect Oil Pump

Likely, you won’t have to replace your pump, so you won’t need to order those parts.

Video

I shot a short video of highlights of the procedure documented in this write-up.

 

Types of Rear Main Seals

The original rear main seal BMW used was white and was spring loaded. It cut a groove into the original, heavier, flywheel’s hub, as I show in the pictures below from my 1973 R75/5, causing oil to leak from the rear main seal.

I expected to see the white seal when I removed the flywheel on this bike along with a single groove in the flywheel hub. But instead, I found a series grooves in the hub and the black/brown “new-style” Teflon (PTFE) seal installed.

The Teflon seal has a set of ridges in the seal lip and it looks like they cut the grooves I found in my flywheel hub. I learned from Tom Cutter of Rubber Chicken Racing Garage, the Teflon seal was put into production starting with the 1983 model year, so my seal could indeed be original, not a replacement of the white seal by a previous owner as I had incorrectly assumed. He suggested the cause for the grooves in the hub is the accumulation of clutch dust on the hub which works its way under the lip of the seal over 40+ years acting as an abrasive.

My concern is these grooves will prevent the new seal from sealing. See the section below, “Removing The Grooves In The Flywheel Hub”, to see how to solve this problem.

Install Rear Main Seal

I use the Cycle Works rear main seal removal/installation tool to install the new rear main seal. But first, I prepare the seal bore and the seal.

Preparation

Before I install the new rear main seal, I clean up the bore with some brake cleaner to remove oil deposits and gunk.

Then I use 1000 grit wet/dry paper and lightly sand the circumference of the bore to get the last bits of baked on seal out of the bore.

I use my blue shop towel and spray a bit of brake cleaner on it and clean the circumference of the seal bore until the towel shows no signs of black residue.

The new seal was included in the EME engine gasket kit and is preformed on a plastic sleeve.

NOTE:
If your seal is not pre-formed so the seal lip is bent toward the rear of the seal, you need to form it. Put a bit of oil on the brown seal lip and then gently push it onto the flywheel hub so the lip is bent and forms a seal around the hub. Let it stay that way for 30 minutes before installing the seal so it will take a set matching the diameter of the hub.

Seal Installation

I use the Cycle Works seal removal/installation tool to install the rear main seal. I don’t use the two small sheet metal screws to install the seal, and I use all five of the flywheel bolts to evenly pull the black plate into the seal bore to seat the new Teflon seal.

I start by putting the seal into the bore as evenly as I can. Then I attach the black plate with all five of the flywheel bolts and tighten them finger tight.

I use a socket wrench with a 19 mm socket and in a cross-wise pattern, I tighten the five bolts a half-turn at a time to pull the seal into the bore. I check the seal as I go to ensure it’s going in evenly and if its too proud on one side, I tighten the corresponding bolt a bit more to keep it from cocking as it slides home.

Eventually the bolts get snug when the hard outer edge of the seal contacts the aluminum lip of the bore. I don’t want to over tighten the bolts and deform the edge of the seal butting against the aluminum lip. But I do snug all five bolts just a bit to be sure they are equally tight so the seal is square in the bore and uniformly against the aluminum lip of the bore.

Then I remove the bolts and the black plate. I visually check all around the seal to be see if  the edge of the seal seems to be the same depth in the bore.

As a second check, I use the back edge of a single edge razor blade as a gauge block. I rest the back edge on the face of the bore in the engine block and slide it around the circumference of the bore. I’m looking to see that it stays in contact with block and doesn’t lift up due to the seal being proud somewhere around it’s edge.

WARNING:
DO NOT USE THE SHARP EDGE OF THE RAZOR as it will nick the surface of the seal. The seal has a hard enough job as it is without being nicked. 🙂

It looks like the seal is square in the bore and up against the aluminum lip.

Install Oil Pump and Cover O-ring

I replaced the oil pump parts–inner rotor, outer rotor and cover–due to the wear I found on them.

I cleaned out the o-ring groove of the new cover to remove some debris I found in it using some steel wool.  Then I cleaned it in my parts washer.

I measure the old oil pump cover o-ring; it is 2 mm thick. I measure the o-rings in the Euro MotoElectrics engine gasket bag of o-rings and find the orange one is the correct o-ring. I compared the new one to the old one just to be sure I have the correct o-ring.

For assembly of the oil pump, I use engine lube, engine oil and blue Loctite.

The engine lube goes on all the oil pump parts to provide lubrication on the first engine start until oil begins to circulate through the oil pump. I use the engine oil to lubricate the oil pump cover o-ring and apply the blue Loctite the the threads of the four 6 mm oil pump cover bolts. I also get out my INCH-pound NOT FOOT-POUND torque wrench to torque the cover bolts.

I apply assembly lube on all the surfaces of the oil pump parts and on the circumference of the oil pump cavity. I fit the inner rotor onto the cam shaft so the flats on the cam shaft line up with the flats on the inside of the inner rotor hole. The faces of the inner rotor are different; one has a flat face and the other is chamfered.  The chamfered face of the inner rotor should go against the engine block with the flat face toward you when you install the inner rotor as shown in the pictures of of the damaged inner rotor below.

I install the outer rotor into the oil pump chamber by rotating it until it slides over the lobes of the inner rotor.

NOTE:
I installed the inner rotor backwards as the chamfered face is pointing toward me instead of toward the engine block as shown in the picture above. This has no affect on operation of the oil pump, so it’s not a problem. The chamfer makes it easier to install the cam shaft on the inner rotor.

I put the oil pump cover o-ring into the groove in the cover and oil it. I also put some engine lube on the cover as the inner and outer rotor can rub against it. I place the cover on the face of the pump chamber. It should fit flush with the engine block without having to push hard.

WARNING:
If the oil pump cover seems to be proud of the face of the pump chamber and you have to push on it to get it to mate with the face, that means the cover o-ring is out of its groove. Don’t tighten the bolts. Remove the cover and reseat the o-ring in the groove. If the pump cover o-ring seems to want to keep popping out of the groove, you can use engine lube on it as it’s a bit sticky, or you could use a small dab of wheel bearing grease to hold it in place

I put a drop of blue loctite on the threads of the four, 6 mm cover bolts and finger tighten them.

I use my INCH-pound—NOT FOOT/pound–torque wrench to torque the cover bolts. I torque them to 75 INCH-pounds–NOT FOOT/pound—in two increments using a cross-wise pattern.

Revisions

2020-01-06  Reorganized and moved flywheel install to separate document.
2020-05-18  Note about which face of inner rotor faces you when you install it.