There was evidence of oil leaks at the rear of the engine when I did the disassembly.  And, with 97,500 miles and 40 years on this R75/5, replacing the seals is a good investment.  I removed the rear sub-frame, rear drive, swing arm, transmission and the clutch before doing the work described here.  You can read about how I removed the other parts in the following pages.

02 BMW R75/5 General Tear Down
– Remove Rear Wheel, Fender and Sub-frame
– Remove Rear Drive
– Remove Swing Arm
– Remove Transmission

Here is the parts list.

Part # Description Qty
11 11 1 338 342 Rear-main Crankshaft Seal 1
11 22 0 016 759 Screw M10x1 24mm, Flywheel 5
11 11 1 256 974 Thrust Washer (Stop Ring), “Blue”
11 41 1 260 182 Oil pump cover 1
11 41 1 335 895 Oil pump cover O-ring 1
07 11 9 913 464 Hex Bolt, M6x16 (Oil Pump Cover) 4

I ordered the following from Cycle Works in Kansas.

I ordered the following from Tom Cutter at Rubber Chicken Racing Garage. Do not reuse the flywheel bolts. They need to be replaced whenever you remove and install the flywheel. Should they break, it gets very expensive. The old style oil cover with Philips head screws has been updated with a new cover design that uses bolts and is a good upgrade when replacing the oil pump cover o-ring.

I used Blue Permatex thread locker and Permatex Ultra-Grey RTV Silicon to stop an oil leak from one of the crankshaft flywheel bolt holes. I used a torque wrench that measures in INCH/pounds, not FOOT/pounds with a range of 20 – 200 INCH/pounds to tighten the oil pump cover bolts and a I used a regular torque wrench to tighten the flywheel bolts.

Secure The Engine & Set Top Dead Center

After I removed the engine from the frame, I put it on my lift and secured it with straps so it was easier to work on.

Make-do Engine Stand Makes it Easier to Work

I moved the connecting rods so they are fully extended which placed the flywheel at top dead center (TDC) with the “OT” mark showing in the timing window. I put rags in the cylinder openings and secured the connecting rods with some wire.

Securing Connecting Rods with Wire at TDC

Blocking the Crankshaft

DANGER: It is absolutely critical to block the crankshaft from moving forward or backward when removing the flywheel.

It you don’t block the crankshaft, it will move off it’s mounting perch and jam when you remount the flywheel. If that happens, you spend big bucks correcting the damage.

I used a 10 mm long bolt from one of the battery terminals and inserted the threaded end into the allen head cap screw that secures the alternator to the crankshaft at the front of the engine. As shown below, the head faces outward.

10mm Long Bolt in Alternator to Block Crackshaft

I mounted the timing cover and hand tightened the three allen head bolts to snug the cover on the head of the 10 mm long bolt in the alternator. I used a socket extension and Allen socket without the socket wrench handle to tighten the blots hand tight. I didn’t want to over tighten the cover bolts and damage the timing cover. This left a small gap between the timing cover and the engine indicating the cover was snugly pushing on the bolt inside the alternator bolt forcing the crankshaft into the rear thrust washer.

I plugged the tachometer cable hole to keep junk from getting inside the front cover area, although I had to put more blue shop towels in the hole after I took the picture :-).

Cover Bolted Down to Block The Crankshaft from Moving Forward

Mark the Flywheel and Secure It

There are five bolts that mount the flywheel to the rear of the crankshaft. To ensure it will mount correctly with the TDC marking on the edge of the flywheel in the timing window when the connecting rods are fully extended, I made several registration marks with a Sharpie pen identifying the bolt at the bottom of the flywheel and a mark at the perimeter. To keep the flywheel from rotating when I removed the flywheel bolts, I used the metal bar I made for securing the flywheel when I removed the clutch and connected it to the top left stud in the engine block. Then I marked where a clutch mounting hole was at the edge of the flywheel, drilled a hole in the bar and secured it to the flywheel using a clutch mounting bolt.

Bottom Bolt and Perimeter Registration Marks and Metal Rod Securing Flywheel

I removed the five bolts holding the flywheel to the crankshaft. One of the crankshaft bolt holes leaked oil.  I learned from Tom Cutter at Rubber Chicken Racing Garage that sometimes these holes crack through to the crankshaft oil passage behind them. Later, I’ll show how he suggested I fix the oil leak.

Flywheel Bolts out And Oil Leak From One Crankshaft Hole

Remove the Flywheel

This turned out to be a bit difficult.  I could not remove it by hand and I did not have the flywheel puller tool available from Cycle Works. I strongly advise you to use a flywheel puller, such as the one I purchased later from Cycle Works . I didn’t think I needed it.  I was wrong.  After 20 mins of effort I got the flywheel off using a technique THAT IS NOT A GOOD IDEA!!!

The Wrong Way to Do It

I decided to try heating the flywheel with a torch and using the clutch bolts to pull it off the crankshaft.  The flywheel would wiggle a little bit off the crankshaft nose, but not very much before the flywheel cooled down.

Heating Flywheel Around Outside of Bolt Holes

Using Long Bolts to To Pull Flywheel by Hand-Doesn’t Work 🙁

Then I used an open end wrench mounted under the head of the bolt with the flat part of the wrench handle placed flush on the edge of the engine housing.  After heating the flywheel around the outside of the bolt holes I would push on the wrench on each of the four bolts to pry it loose. In retrospect

WRONG IDEA !!!! 10mm Wrench Under the Four Bolts to Pry Flywheel Off


The transmission has to mount flush against the engine all the way around, so if had I cracked the lip of the housing or flattened it, I would have had a real problem.  Also, heating the flywheel when it is mounted on the nose of the crankshaft won’t get much expansion as both are steel and the heat difference won’t be very much.

The Right Way to Remove the Flywheel

After I removed the flywheel, I bought the Cycle Works tool and ended up using it to remove the flywheel several times for reasons that will become clear later on.  Here is the right way to remove the flywheel in about 3 minutes with no need to head the flywheel.

Axle Grease on Ball Bearing of Big Bolt

Cycle Works Flywheel Puller Mounted on Flywheel

Cycle Works Flywheel Puller Center Bolt Pulling Flywheel off Crankshaft

The Cycle Works flywheel puller can also be used to hold the flywheel when removing the five flywheel bolts. I had made my own tool that doubled to block the flywheel when tightening or removing the clutch bolts, but this is a handy tool.

Cycle Works Flywheel Puller Can Be Used to Block Crankshaft When loosening Flywheel Bolts

Clean Up the Rear Engine Housing

The back end of the engine housing where the transmission and clutch go was a mess. It looks like oil has been leaking from the oil pump cover mixing with the dust from the clutch to create a lot of grunge.

Rear Main Seal & Engine Housing Grunge

Oil Pump Cover & Engine Housing Grunge

I put a lot of newspaper on the shop mat and then I cleaned up all the grunge with a couple cans of foamy engine cleaner, toothbrushes and nylon bristle brushes until it was shiny again.  I used a spray bottle of water to wash off the engine cleaner and oil and then cleaned it again with some brake cleaner to remove the last traces of grunge. I don’t want the crud to get on the new rear main seal or o-ring.  The newspaper soaked up a lot of the dirty water and I mopped up the small amount remaining on the shop mat with blue paper shop towels.

Engine Degreaser

Cleaned Housing, 5# Lighter and Ready to Start Work

Clean Up the Flywheel

I inspected the flywheel and there are some burrs on the teeth on the perimeter of the flywheel that the starter motor engages the flywheel.  By the  way, the 45 degree angle on the teeth is not caused by wear but is machined to allow the flywheel teeth to engage with the starter motor gear.  That gear runs at 90 degrees to the flywheel, so there has to be a 45 degree angle cut into both the flywheel and the starter motor gear teeth.

Flywheel Teeth Show Some Wear and Burrs from Starter Motor

Flywheel Teeth Show Some Wear and Burrs from Starter Motor

In checking the wisdom on the BMW Airhead forum on micapeak, the consensus is the teeth are not bad, but should be filed with a flat file to remove the burrs on the edge of the teeth.

The outside of the flywheel hub rubs against the rear main seal and wears over time, as is evident in the picture below. The older style rear main seal has a narrow contact patch on the hub which cuts a narrow groove over time. This wear can lead to oil leaking past the old style rear main seal and required old style replacement seals to be located so they contacted an unworn part of the hub.  The new seal that I am using has a larger contact patch and I don’t need worry about installing it so it avoids the wear ring in the hub.

Flywheel Wear Groove from Rear Main Seal

The consensus is this is not a deep groove and the flywheel is still serviceable. The rest of the hub doesn’t show any damage, although there is discoloration caused over time.

Flywheel Hub with Discoloration

Tom Cutter suggested that I polish the hub with metal polish until the discoloration was removed. Below is the hub after cleaning it up.

Flywheel Hub After Using Metal Polish to Remove Discoloration

Finally, I put some Testor’s model paint on the timing marks and letters on the rim of the flywheel to make it easy to see them: yellow for “OT”, white for “S” and red for “F”.  The flywheel is ready for installation.

Replace Oil Pump Cover and O-Ring

The oil pump cover has been redesigned and uses 10 mm bolts instead of Philips head screws.  You can not use the Philips head screws with the new cover, but why would you want to?  It’s much easier to torque bolts and remove them.  Removing the old screws requires an impact driver to get them loose, or you will likely strip out the heads with a screwdriver.

Impact Driver

A couple of raps with the mallet and they loosened up so I could remove the pump cover.

Removing Oil Pump Cover Phillips Head Screws with Impact Driver

When the cover is removed, the pump gears are visible: and inner four-lobe rotor and an outer five-lobe hypocycloid chamber. Each has a punch mark and they should be facing you when the pump parts are installed correctly as shown below.

Oil Pump Showing Punch Marks on Rotor and Hypocycloid Housing

I removed them to check for any damage. The four-lobe rotor is secured on the oil pump shaft with a woodruff key, and in my case, the key was on the bottom of the shaft which is visible in the photo below. I used cam lobe grease to hold the woodruff key in the slot on the oil pump shaft against gravity when I put the four-lobe gear back on the shaft.

Greased Oil Pump Hyocyclod Housing

Greased Oil Pump Rotor

I put some grease on the wearing surfaces of the pump rotor and the hypocycloid gear. This  will provide some lubrication when the engine starts until the oil circulates in the pump, and it may be while before the engine starts again so just squirting oil on the gears  may not provide sufficient lubrication during the first engine start.

Here is the new (left) and old (right) oil pump covers.

New Cover (Left) with 10 mm Bolts and Old with Philips Head Screws

Here are the new (red) and old (black) pump cover o-rings. The old o-ring is flattened and hardened and that lets the oil leak past the cover.

New O-Ring (red) and Flattened Old O-Ring (Black)

I put the new o-ring into the groove on the backside of the pump cover using some thick grease to help keep it in the groove so it wouldn’t shift when I put the new cover on and get pinched.

Grease to Hold Oil Pump Cover O-ring

I put Blue Permatex thread locker on the new 10 mm bolts. The bolts are tightened to 72 – 76 INCH/pounds, NOT FOOT POUNDS. I didn’t have a torque wrench that measures in INCH/pounds, so this was an opportunity to add one to the tool box.

Blue Permatex for Oil Pump Cover Bolts

The oil pump cover only goes one way as the top holes are closer together than the bottom ones. You can see the beveled edge of the cover goes at the top. I finger tightened the Permatexed bolts into the cover.

New Oil Pump Cover Installed

I then torqued them to 72 INCH/pounds in increments in a cross-wise pattern.

Torque Oil Pump Cover Bolts to 72 INCH/pounds

All done and the bike has a new oil pump cover and o-ring.

Repair the Leaking Crankshaft Bolt Hole

Tom Cutter suggested using RTV to seal the leak at the bottom of the crankshaft bolt hole. I used Permatex Ultra Grey Ridgid High Torque RTV Silicone.

Permatex Ultra Grey RTV

I wanted to be sure I didn’t get any of it on the threads, and I wasn’t sure how deep the tapered nozzle would go into the hole. So I made some measurements. The flywheel bolt has a shoulder under the head that fits the hole in the flywheel and rests on the face of the crankshaft, so that is how far the bolt will go into the crankshaft.

Flywheel Bolt Shoulder Stops Bolt at Crankshaft Face

I put the nozzle of the RTV tube into the hole and marked it to see how deep it would go.

Checking Depth of Nozzle

Then I compared that to the bolt to see if the nozzle was going past the threads.

Depth of Bolt vs Depth of Nozzle

And, it does go deeper than the threads. So, if I insert the nozzle all the way into the hole and give a squeeze, the silicone will fill the void below the threads. I put a little into the hole and then ran the flywheel bolt all the way in to check the depth of the RTV and then added a little more and checked again until the bottom of the bolt just touched the RTV silicone to ensure I didn’t over fill the void and get silicon on the threads.

Use Flywheel Bolt to Check Depth of RTV Silicone

Here is the crankshaft hole with the Ultra Gray RTV silicone at the bottom. I let this set over night before continuing.

RTV Silicone at the Bottom of Crankshaft Bolt Hole

Pull the Rear Main Seal

I bought the Rear Main Seal Puller tool from Cycle Works.

Cycle Works Rear Main Seal Puller Kit

I used the following to pull the rear main seal: the disk, the sheet metal screws and two of the flywheel bolts.

Rear Main Seal Puller Disk with Screws and Flywheel Bolts

I attached the disk to the crankshaft with the flywheel bolts and then screwed the sheet metal screws into the edge of the rear main seal.

Mount Puller Disk with 2 Flywheel Bolts and Screw in Sheet Metal Screws

When the screws bottomed out I stopped since that indicated they had penetrated the outer ring of the seal. The screws will not be flush with the black disk, but will be proud of it as shown below.

Sheet Screw Inserted Until it Bottomed Out

Then I threaded the large bolt into the center hole until it pressed on the end of the crankshaft.

Center Bolt Screwed In to End of Crankshaft

I had to use a crescent wrench to turn the bolt to pull out the old seal. After some initial resistance, it came out easily.

Tightening Bolt to Pull Oil Seal

Puller Cover with Old Oil Seal

I backed out the sheet metal screws to remove the old seal from the black puller disk. As shown here, there is a metal thrust washer, aka. stop disk, behind the rear main seal that slips over two pins in the engine case. I didn’t intend to replace the thrust washer.  Make sure it’s on the pins with the white radial stripes facing you before you install the new seal.

Stop Disk Mounts on Pins

Install New Rear Main Seal

The old seal design has a narrow contact area and a metal spring in the back.

Front Side of Old Rear Main Seal

Backside of Old Rear Main Seal with Metal Spring

But the new seal does not and has a larger contact strip.  It is made of PTFE, which is a Teflon material.

Front Side of New Rear Main Seal

Back Side of New Rear Main Seal

BMW published a service bulletin in 1988 on how to prepare the new seal for installation. Advice I received on the Micapeak BMW Airhead forum suggested heating the seal in 150 F oil to soften it prior to forming it on the flywheel hub.

Heating the seal to 150 F to soften it is not required. I no longer bother with this step. I preshape it on the nose of the flywheel before installing it.

150 F Oil to Soften Rear Main Seal

I let the seal sit for about 10 minutes and then pushed it onto the hub of the flywheel to form the seal around the hub, and then removed it so I can install the preformed seal in the engine.  When doing this, the back side of the seal faces you and the front side is against the face of the flywheel. The earlier pictures show the back and front sides of the seal.

Forming Seal on Flyhwheel Hub

These are the parts I used to install the seal back in the engine: the puller disk, the flat washers and the flywheel bolts.

Rear Main Seal Installation Parts

I inspected the aluminum housing that the seal fits into to be sure there were no sharp edges that could damage the seal. If there were any, 600 wet sandpaper can be used to dress the edges. I sprayed the engine housing with brake cleaner to be sure it and the crankshaft are clean and there is no grit or contamination on the surfaces. Then I put the stop ring back in place on the pins in the engine housing. You can see the top left pin at the 10:00 position and bottom right pin at the 4:00 position just behind the stop ring in the picture below.

DANGER: It is very important to be sure the rear thrust washer STAYS on the pins.  Even when the rear main seal is installed, it is possible for the thrust washer to come off the pins. 

Rear Thrust Washer Mounts on Pins in the Crankshaft Boss

I used a heat gun to heat the aluminum housing to about 150 F to help ease the seal into the hole.

Heating Aluminum Housing Around Rear Main Seal Hole

I pressed the new seal that had been formed on the hub of the flywheel by hand into the engine casing trying to keep it aligned as much as possible.

Starting Rear Main Seal into Hole

Then, I used the flywheel bolts with washers to mount the black disk on top of the seal and finger tightened all the bolts checking that seal was aligned in the hole.  Where it was a bit proud, I tightened the corresponding flywheel bolt a bit more until it was even.

Installing Rear Main Seal

Using a cross-wise pattern I tightened each bolt a half-turn until the seal bottomed out on the land in the engine case. This set the seal all the way into the hole. This is correct for the new seals and you don’t have to worry about positioning the seal so it doesn’t line up with the wear ring in the flywheel hub. The new seal design has a large contact area and will seal over wear rings in the flywheel hub when it is pulled all the way into the hole.

Rear Main Seal Installed Flush with Engine Housing

Install the Flywheel

DANGER: Do Not Reuse the old flywheel bolts. Install it ONLY with new bolts. The flywheel  bolts are designed to stretch when torqued. They should not be reused.

After the difficulty I had removing the flywheel, I purchased the Cycle Works flywheel puller to help with installation.

Flywheel Removal & Installation Tool

I heated the flywheel around the bolt holes with a propane torch.

Heating Flywheel Bolt Circle

It took about 5-10 minutes to get it to 200-220 degrees as measured with my infrared remote thermometer.  Using the spit method, this would be “sizzle hot”.

Heated to 220 F

I attached the flywheel puller using the long bolts in the puller kit and used welding gloves to handle the flywheel so I wouldn’t burn myself.

Flywheel Removal Tool Used as Handle

Then, I checked that the crankshaft was still positioned so the pistons are at top-dead-center: I made sure the connecting rods were fully extended, and confirmed the timing mark was at OT in the timing window.  Then when I had pushed the flywheel onto the crankshaft a bit, I checked the registration marks at the perimeter were in the same position as when I removed the flywheel.

Confirming TDC of Connecting Rods

Confirming TDC of “OT” Mark on Flywheel

Confirming TDC of Registration Marks

The OT mark doesn’t have to be precisely in the window since misalignment would be one or more bolt holes off and each of those is 72 degrees so it would be very obvious the flywheel was not aligned correctly on the crankshaft.

DANGER: Before you put the flywheel on the crankshaft, check to see that the rear thrust washer is still on the pins.  Reach inside and try to rotate the thrust washer with two fingers. It should not rotate. If it does, it is off the pins. You can get it back on the pins by pulling it forward and turning it so the holes in the thrust washer align with the pins and the thrust washer is pushed back against the boss in the engine.

What Happens If Thrust Washer Comes Off Pins 🙁

The first time I did this job, the thrust washer came off one of the pins. I discovered this AFTER torquing the flywheel and removing the bolt in the alternator that blocked the crankshaft from moving. I put an Allan wrench in the alternator bolt to turn the engine and it would not move. THIS IS BAD.

I removed the flywheel and looked at the rear thrust washer. It was on the top left pin, but the bottom right pin was partially obscured by metal.  I removed the rear main seal and inspected the trust washer. The holes were not round and there was shiny metal where the thrust washer had contacted the flywheel on the front side.

Front of Damaged Thrust Washer-Out of Round Holes, Shiny Area Around Lower Right Hole

Inspection of the backside showed gouges where the pins had deformed the thrust washer. The lower right pin had deformed the metal and created a semi-circle of material in half of the hole. Fortunately the pins were not broken off nor was the boss damaged, both of which could have easily happened. However, the top of the lower right pin was beveled and I had to carefully use a small file to clean the burr on the edge off so the new thrust washer would seat all the way to the engine boss. I GOT VERY LUCKY 🙂

Back of Damaged Thrust Washer-Gouges from Pins Forced Into Back of Thrust Washer

Bottom Right Pin Beveled As It Gouged the Thrust Washer

I think I jarred the thrust washer off the lower pin when I used a rubber mallet to drive the heated flywheel onto the crankshaft. The vibration caused the thrust washer to move. 

Install New Rear Thrust Washer

I ordered a new rear thrust washer of the same thickness as the damaged one, new flywheel bolts (they are not to be reused as they stretch when torqued down) and a new rear main seal.  Thrust washers come in different thickness to adjust the crankshaft end play. Using the partial part number on the back of my original one and also a caliper, I confirmed it was a “Blue” size, so I ordered the same size to replace it.  Here is the new thrust washer with the blue dot.  It was very close to  the thickness of the original one so the old thrust washer hadn’t worn much in 97,500 miles.

New “Blue” Size Thrust Washer

And here is a comparison of the new thrust washer and the damaged one.

New Thrust Washer (Left) and Damaged (Right)

This time, before I mounted the crankshaft, I checked to be sure that the thrust washer was still centered firmly on the pins.

Bottom Right Pin Correctly in Thrust Washer Hole

Top Left Pin Correctly in Thrust Washer Hole

Checking Thrust Washer is On the Pins

I used the flywheel removal bar to press the heated flywheel onto the crankshaft.  When it had slid firmly onto the crankshaft, I used the flywheel bolts to draw it onto the crankshaft tightening them a half turn at a time in a cross pattern.  I rotated the flywheel back and forth when it got close to being fully seated onto the crankshaft to be sure I could not feel any increased resistance to rotation.  If I felt any, then the trust washer was off the pins again, but I would know it and can fix this before I torqued the flywheel bolts and break things.

Torque Flywheel Bolts

When the bolts seated I backed them off 1/16 turn so the shoulder of the bolt is still in the flywheel hole and let the flywheel cool down to room temperature. Then I wiggle the flywheel clockwise and counterclockwise to be sure the flywheel is centered on the bolts and finger tighten the bolts. Once again, I made sure the flywheel and crankshaft rotate without any increased resistance.

Flywheel Bolt and Shoulder Under the Head

Then I mounted the flywheel removal tool to the right side stud in the engine and bolted it to the flywheel using the two long bolts in the puller kit, although a single bolt will work.

Blocking Flywheel From Turning with Flywheel Removal/Installation Tool

The torque setting for the flywheel bolts is 45 – 50 Foot/Pounds. I set the torque wrench to 47 Foot/Pounds. I tightened the bolts in a cross-wise pattern in increments until the torque wrench slips. Here is the installed flywheel.

Flywheel Mounted and New Bolts Installed


This content was originally published here.