11 BMW 1983 R80ST Replace Rear Main Seal

I’ve removed the airbox, transmission, clutch and flywheel to gain access to the rear main seal so I can replace it. You can see how I did that work here.

I’ve published documents on replacing the rear main seal on other projects. Here are links to those documents.

Since the 1983 R80ST engine is similar in many ways to the 1983 R100RS, I will link to the 1983 R100RS documents as appropriate in this document.

Tools

I typically use the Cycle Works tool for removing and installing the rear main seal.

Cycle Works Rear Main Seal Tool

Cycle Works Rear Main Seal Tool

That said, on this bike, I had to resort to getting a “bigger hammer” as the seal was very tight in the bore. So I used a hooked seal puller to carefully remove the seal without scratching the aluminum bore it fits in.

Hook Style Seal Puller

Hook Style Seal Puller

Parts

The new rear main seal is part of the Euro MotoElectrics seal kit, EME Part # GSK-EngineKit421, and is BMW Part# 11 11 1 338 342.

New Rear Main Seal in EME Engine Gasket Kit

New Rear Main Seal in EME Engine Gasket Kit

New Rear Main Seal Comes Pre-formed Around Plastic Sleeve

New Rear Main Seal Comes Pre-formed Around Plastic Sleeve

It has a plastic cylinder inside the seal to keep the lip of the seal at the correct diameter to fit around the guide ring that mounts on the nose of the crankshaft. I remove the white plastic ring before installing the seal.

Rear Main Seal And Seal Lip

Rear Main Seal And Seal Lip

Video

Here is a short video of how I do this work on the 1983 R80ST.

VIDEO: 1983 BMW R80ST Replace Rear Main Seal

Preparation

Before I start work, I clean the bell housing so I don’t get any dirt, grunge or grit inside the engine when I remove the rear main seal. Since the top engine compartment was also dirty and oily, I removed the starter motor so I can clean it at the same time. I also removed the rebreather hose, which I plan to replace, so it is easier to clean the top engine compartment. I plugged the hole in the rebreather spigot with some blue shop towel to keep water out of the engine.

Bell Housing Crud

Bell Housing Crud

Bell Housing Crud

Bell Housing Crud

Top Engine Housing Crud After Starter Motor Removed

Top Engine Housing Crud After Starter Motor Removed

Top Engine Housing After Crankcase Breather Hose Removed: Spigot Plugged With Piece Of Blue Shop Towel

Top Engine Housing After Crankcase Breather Hose Removed: Spigot Plugged With Piece Of Blue Shop Towel

I use kerosene and a stiff brush to remove the hardened gear oil. Then I use Gunk Foamy Engine Cleaner to remove the kerosene and a lot more of the dirt and baked on gear oil. Finally, I use a toothbrush and some brake cleaner to get into the corners of the casting and get out stubborn dirt and gear oil. When I’m done, the inside of the bell housing shines again.

Cleaning Agents: Kerosene, Gunk Foamy Engine Cleaner, Carburetor Cleaner

Cleaning Agents: Kerosene, Gunk Foamy Engine Cleaner, Carburetor Cleaner

Time For A Bubble Bath In Gunk Foamy Engine Cleaner

Time For A Bubble Bath In Gunk Foamy Engine Cleaner

Time For A Bubble Bath In Gunk Foamy Engine Cleaner

Time For A Bubble Bath In Gunk Foamy Engine Cleaner

Before Using Carburetor Cleaner

Before Using Carburetor Cleaner

Before Using Carburetor Cleaner

Before Using Carburetor Cleaner

Bell Housing Is Spotless

Bell Housing Is Spotless

Top Engine Housing Is Clean

Top Engine Housing Is Clean

Top Engine Housing Is Clean

Top Engine Housing Is Clean

Remove Rear Main Seal

This link shows how I do that work.

Here are some pictures from the 1983 R80ST. On this bike, the steel sleeve of the seal was so hard I couldn’t screw in the puller screws of the Cycle Works tool. Instead, I tightened the puller screws as tight as I could by hand to mark the edge of the seal. I put a piece of blue shop towel behind the seal to keep the steel shavings from falling inside the engine. Then I drilled 7/16″ holes in the face of the seal and screwed in the puller screws.

Mark From Extraction Screw On Steel Face Of Rear Main Seal

Mark From Extraction Screw On Steel Face Of Rear Main Seal

Drilling 7/16" Hole In The Edge Of The Rear Main Seal

Drilling 7/16″ Hole In The Edge Of The Rear Main Seal

7/16" Hole Drilled Into Face Of Rear Main Seal

7/16″ Hole Drilled Into Face Of Rear Main Seal

I was not able to remove the rear main seal using the Cycle Works tool. It was stuck tightly in the bore and the screws pulled out of the edge of the seal. I repositioned the puller and and drilled new holes in the face of the seal. Then I used my MAP gas torch and heated the engine block around the perimeter of the seal. Again, the screws pulled out of the seal.

Seal Puller Secured With Two Extraction Screws Into Rear Main Seal

Seal Puller Secured With Two Extraction Screws Into Rear Main Seal

Tighten Puller Bolt To Remove Rear Main Seal

Tighten Puller Bolt To Remove Rear Main Seal

Puller Screw Pulled Out Of The Hole

Puller Screw Pulled Out Of The Hole

So, I used my seal puller. I used the short hooked end and carefully pried the seal out of the bore by walking around the seal to get it loose. I was very careful to put the point of the hook of the seal puller inside the channel at the edge of the seal so I don’t damage the aluminum bore in the engine block the seal fits inside of. That technique worked.

Seal Puller-I Use The Short Hook End To Get Behind The Seal

Seal Puller-I Use The Short Hook End To Get Behind The Seal

Using Seal Puller To Remove Rear Main Seal By Working Around The Perimeter

Using Seal Puller To Remove Rear Main Seal By Working Around The Perimeter

Rear Main Seal Removed-Finally

Rear Main Seal Removed-Finally

Install Rear Main Seal

This link shows how I do that work

Here are some pictures from the 1983 R80ST.

Oiling Edge Of Rear Main Seal Before Installation

Oiling Edge Of Rear Main Seal Before Installation

Aligning Rear Main Seal In Bore Before Installing Cycle Works Seal Tool

Aligning Rear Main Seal In Bore Before Installing Cycle Works Seal Tool

Cycle Works Rear Main Seal Installation Tool Attached

Cycle Works Rear Main Seal Installation Tool Attached

Using Flashlight To Verify Seal Is Flush With Edge Of Bore In The Case

Using Flashlight To Verify Seal Is Flush With Edge Of Bore In The Case

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