11 BMW 1983 R100RS Remove Flywheel & Rear Main Seal

I remove the flywheel so I can replace the rear crankshaft main seal and the oil pump cover o-ring. In order to get to the flywheel, I remove the transmission and the clutch as I show in these write-ups.

I removed the engine from the frame and put it on my large work bench since I am powder coating the frame. But this work can be done with the engine in the frame.

Engine Out of Frame On The Workbench

Engine Out of Frame On The Workbench

Tools

I use an impact wrench to remove the flywheel bolts. This makes it easy to remove them without having to immobilize the crankshaft to keep it from turning.

Impact Wrench with 19 mm Socket Removes Flywheel Bolts Easily

Impact Wrench with 19 mm Socket Removes Flywheel Bolts Easily

Rear Main Seal Removal Tool From Cycle Works

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

Cycle Works Rear Main Seal Tool

Cycle Works Rear Main Seal Removal/Installation Tool

Video

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

Avoiding Disaster

Since I’m going to remove the flywheel after I remove the clutch, I need to avoid a disaster involving the crankshaft front thrust washer coming off it’s mounting pins. If that happens, I have to remove the crankshaft to get it back on the pins, which isn’t a disaster but a real PITA. Should I not notice that the thrust washer is off the pins and then tighten the flywheel bolts, there is a high likelihood of damaging the crankshaft and crushing the pins that are cast into the engine block, which is a true disaster.

The way to prevent the front thrust washer from coming off it’s mounting pins is to force the crankshaft to the rear so it butts up against the thrust washer. I do that by putting a short, 12 mm long, 6 mm Allan head bolt into the recess of the alternator rotor’s Allan head bolt that attaches the rotor to the crankshaft.

M6x12 Bolt For Pushing Crank Against Front Thrust Washer

M6x12 Bolt For Pushing Crankshaft Against Front Thrust Washer

M6x12 Allan Bolt Inserted Into Alternator Rotor Allan Bolt Recess

M6x12 Allan Bolt Inserted Into Alternator Rotor Allan Bolt Recess

Then I install the front engine cover using the two bolts and finger tighten them so they pull the front cover tight against the head of the 6 mm bolt.

WARNING:
DO NOT OVER TIGHTEN the two front cover bolts or you can damage the alternator rotor bolt and/or front engine cover. You just need to snug them up by hand. And, it you have the earlier model front cover with a third cover bolt at the bottom, you don’t need to install that bolt.

When the M6x12 bolt is correctly installed, there is a slight gap between the front cover and the engine block at the bottom of the cover. That gap is your sign you have safely pushed the crankshaft up against the front thrust washer and you can safely remove the flywheel.

Hand Tighten Front Engine Cover Bolts-DO NOT OVER TIGHTEN

Hand Tighten Front Engine Cover Bolts-DO NOT OVER TIGHTEN

Gap At Bottom of Front Cover Shows Cover is Firmly Against M6x12 Bolt and Crankshaft Is Against Front Thrust Washer

Gap At Bottom of Front Cover Shows Cover is Firmly Against the M6 Bolt

Secure Engine to Work Bench

I don’t have an engine stand, so I secure the engine to my work bench. I use a 2×4 under the front timing chest cover to keep the engine from tipping forward and I use two ratchet straps connected together to clamp the engine to my bench top by passing the strap under the bench and over the engine’s top cover so the engine won’t move around as I work on it.

Securing Engine to Work Bench with 2x4 Under Timing Chest Cover

Keeping Engine From Tipping Forward with 2×4 Under Timing Chest Cover

Securing Engine to Work Bench with Ratchet Strap

Securing Engine to Work Bench with Ratchet Straps

After I secure the engine block to my work bench it’s easy to see there has been some oil leaking out of the rear of the engine onto the shelf above the oil pan. So, something is leaking, either the rear main seal, the oil pump cover o-ring or the flywheel o-ring.

Signs of Oil Leaking From Rear of Engine

Signs of Oil Leaking From Rear of Engine

Set Crankshaft To Top Dead Center (TDC)

It’s important to set the crankshaft at TDC before removing the flywheel. I need to mark the flywheel and engine with index marks so when I install the flywheel again, it will be attached to the crankshaft in the correct orientation. I put some white paint next to a flywheel bolt and add a line on the engine block that aligns with that bolt.

WARNING:
If the flywheel is rotated by one crankshaft bolt hole from where it should be on the crankshaft, the crankshaft will be out of synch with the flywheel by 72 degrees and the ignition timing marks on the flywheel will be out of synch by 36 degrees since ignition timing is defined by the camshaft and the camshaft rotates at one-half the speed of the crank.

Flywheel and Crankshaft Set to TDC

Flywheel and Crankshaft Set to TDC

Flywheel & Engine Block Index Marks

Flywheel & Engine Block Index Marks

Remove Flywheel From Crankshaft

I use my impact wrench with a 19 mm socket to remove the flywheel bolts. This is a quick way to get them off since I don’t have to block the flywheel to keep it from turning.

Removing Flywheel Bolts with Impact Wrench

Removing Flywheel Bolts with Impact Wrench

Flywheel Bolts Coming Out

Flywheel Bolts Coming Out-Note Index Marks on Flywheel and Engine Block at 10:00 Position

With the bolts removed, I could see a little oil around the bolt holes. It likely is coming from a leaking flywheel o-ring.

Small Amount of Oil Next to Bolt Holes

Small Amount of Oil Next to Bolt Holes

I need to pull the flywheel off the rear crankshaft nose. I put three clutch bolts screwed into every other hole in the flywheel. Then I use my vice grips (you could use pliers but the vice grips were handy) to grab each clutch bolt and give it a tug and a wiggle. I work my way around the flywheel tugging and wiggling the three bolts. It took me two times around the flywheel to pull it free from the crankshaft.

Three Clutch Bolts Installed Symmetrically Help Me Pull The Flywheel Off The Crankshaft

Three Clutch Bolts Installed Symmetrically Help Me Pull The Flywheel Off The Crankshaft

Grabbing Clutch Bolt To Give A Tug

Grabbing Clutch Bolt To Give A Tug

Once I get the flywheel off, I put a paint mark next to the crankshaft bolt hole that aligned with the paint mark I put on the engine block when I added the index marks to the flywheel and engine block. I also decided to add a couple punch marks onto the face of the crankshaft nose and the flywheel hole so if the paint comes off when I clean the inside of the bell housing and the flywheel, I’ll know which crankshaft bolt hole to index the flywheel to.

Punch Marks Added to Crankshaft Near Marked Bolt Hole

Punch Marks Next To Flywheel Bolt Hole

Punch Marks Next To Flywheel Bolt Hole

The back of the flywheel has a sleeve that fits over the rear nose of the crankshaft. The older, spring loaded, sharp edged seal was not used in 1983. The older seal cuts a groove into the flywheel hub over time leading to oil leaks. Starting in the 1983 model year, a new teflon (PTFE) seal was used. The seal I have in the engine block is the new teflon one.

Newer Teflon (PTFE) Seal Was Installed

Newer Teflon (PTFE) Seal Was Introduced In The 1983 Model Year

You can see in the shiny band around the hub some grooves in the outside of the hub. The grooves are likely caused by clutch dust getting under the seal and acting as an abrasive.

Flywheel Sleeve Shows Some Grooves From the Rear Main Seal

Flywheel Sleeve Shows Some Grooves From the Rear Main Seal

The front face of the flywheel has the BMW part number stamped on it.

Flywheel Has BMW Part Number Stamped On It

Flywheel Has BMW Part Number Stamped On It

And, there is a paint mark on the flywheel teeth showing the heavy part of the flywheel. The clutch cover plate and pressure plate also have factory paint marks. When assembling the clutch on the flywheel, the heavy part of each component should be installed 120 degrees from each other. This ensures the engine is as balanced as possible which reduces engine vibration.

Clean Bell Housing & Flywheel

Before I remove the oil pump cover, or replace the rear main seal, I clean the bell housing, and while I’m at it, the flywheel. I want the bell housing to shine and I don’t want any oil or clutch dust on the flywheel. I don’t want any of the garbage and grunge caked on the bell housing to get into the engine.

I start with kerosene and a paint brush. I brush the kerosene all over the inside of the bell housing and scrub as much of the grunge off as I can. Then I use the foamy engine cleaner to lift more of the oil and clutch dust out while removing any traces of the kerosene. Last, I use carburetor cleaner, a tooth brush and blue shop towels to get the stubborn deposits off the inside of the bell housing.

WARNING:
Wear rubber gloves while doing this as these solvents are not good for you when they get on your skin. Its a good idea to wear protective glasses as well as the carburetor cleaner can splash back at you.

Solvents I Use to Clean Bell Housing Until It Shines

Solvents I Use to Clean Bell Housing Until It Shines

Engine Ready For Cleaning In a Pan To Catch The Solvents

Engine and Flywheel Ready For Cleaning In a Pan To Catch The Solvents

Bath Time with Foaming Engine Cleaner

Bath Time with Foaming Engine Cleaner

When I’m done, the inside of the bell housing shines and it’s clean enough to eat off of.

Nice and Clean :-)

Nice and Clean 🙂

Remove Rear Main Seal

After I cleaned the bell housing until it shines, I use the Cycle Works tool to remove the rear main seal. I attach the black disk to the crankshaft nose using two flywheel bolts that I snug down by hand to center the black disk on the crankshaft.

Rear Main Seal Fits Into Bore in Engine Block Around the Crankshaft Nose

Rear Main Seal Fits Into Bore in Engine Block Around the Crankshaft Nose

Secure Cycle Works Black Disk Using (2) Flywheel Bolts and Hand Tighten

Secure Cycle Works Black Disk Using (2) Flywheel Bolts and Hand Tighten

Then I screw in the two sheet metal screws into the two small tapped holes at the outside edge of the black disk. I had to use my electric screw driver to drive them all the way in as the seal is pretty hard.

Tighten Sheet Metal Screws Into Seal Until Screw Heads Are Flush With Black Disk

Tighten Sheet Metal Screws Into Seal Until Screw Heads Are Flush With Black Disk

After the two sheet metal screws are securely screwed into the seal, I remove the two flywheel bolts. Then I screw in the large diameter puller bolt into the threaded hole in the center of the black disk until it’s snug against the face of the flywheel. I use a crescent wrench to tighten the bolt which pulls the rear main seal out of the engine block.

Removing Seal with Puller Bolt After Removing (2) Flywheel Bolts

Removing Seal with Puller Bolt After Removing (2) Flywheel Bolts

Old Seal Removed And Screwed to Black Plate

Old Seal Removed And Screwed to Black Disk

Old Seal Removed (Note Holes in Edge From Sheet Metal Screws)

Old Seal Removed (Note Holes in Edge From Sheet Metal Screws)

NOTE:
If your rear main seal doesn’t come out easily, or the sheet metal screws pull out of the seal, try heating the engine block around the seal with a heat gun. Then rotate the black disk so the two sheet metal screws cut new holes in the seal and try again.

Heating Around Rear Main Seal if Seal Won't Come Out Easily

Heating Around Rear Main Seal if Seal Won’t Come Out Easily

Revisions

2019-11-20  Edits and typos.

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