I completed work on the front of the engine when I replaced the timing chain, crankshaft timing gear, front main seal and crankshaft nose bearing. I also replaced the three seals in the timing chest cover.  You can see how I did that work here:

• 11 BMW 1977 R100RS Replace Timing Chain, Crankshaft Timing Gear & Nose Bearing

So the next area of work is the rear of the engine. I removed the clutch and had it refurbished by Southland Clutch. I removed the flywheel, replaced the rear crankshaft main seal and the oil pump cover o-ring. While I had the pump cover off, I measured the clearances of the oil pump gears and found them all good and toward the low end of the allowable wear limit. Here is how I did this work:

• 21 BMW 1977 R100RS Remove, Refurbish, Install Clutch
• 11 BMW 1977 R100RS Replace Rear Main Seal & Oil Pump Cover O-Ring

I added a new full advance timing mark to the flywheel at 25° BTDC. I have dual plug heads and the advice from Tom Cutter at Rubber Chicken Racing Garage is to retard the full advance by 6° by retarding the “S” timing by 3° and limiting the full advance by another 3°. Before doing this, I did some digging to learn more about the flywheel in this bike and the automatic timing unit (ATU) and documented BMW flywheel changes in the /5, /6 and /7-R100 series of motors and the ATU’s.  You can find that information here:

• 12 BMW 1977 R100RS Changes To Ignition For Dual Plug Heads
• 12 BMW 1977 R100RS Install Dyna III Electronic Ignition-Refurbish Automatic Timing Unit (ATU)

Next up is to remove the pistons, rings and connecting rods, see how the rod big end bearings look, remove the rings, clean the pistons and inspect them and then make decisions about what needs to be done.

Here are a couple pictured from the write-up.

M6 x 10 mm Bolt In Alternator Rotor Allen Head Bolt

Front Cover Snug with Gap At Bottom Ensures Flywheel is Blocked Toward Rear

Ready To Remove Clutch

Accumulated Crud on Transmission Shelf

Clutch Removal Bolts-Nut Distance From Bolt Head

Clutch Alignment Marks

Diaphragm Spring with Streaks of Lubricant 🙁

New Diaphragm Spring Height & Partial Part Number (Right)

Added Flywheel Index Marks

Oil Leak From Crankshaft Bolt Hole (1:00)

Groove Cut Into Flywheel By Rear Main Crankshaft Seal

Starting To Clean Bell Housing

Bell Housing After Cleaning

Timing Marks Painted for Visibility

Flywheel Timing Marks with added 25 Degrees BTDC Mark

New Flywheel Hub O-ring

Engine Strapped To Work Bench Before Torquing Flywheel Bolts

I’m going to have the swing arm powder coated. So I remove the drive shaft to avoid any possibility of damage to it and the swing arm bearings. I will replace the swing arm bearings as they are likely 40 years old and there is rust in many places on the bike so it’s possible the swing arm bearings have not been cared for.

Swing Arm with Drive Shaft Inside

I use a tool from Cycle Works to pull the bell housing off the end of the drive shaft that fits into the rear drive unit. Then the shaft slides out of the swing arm housing toward the transmission end of the swing arm. The tool made it very easy to remove the bell housing. The housing is secured by a nut that is torqued quite high and by a taper in the housing and the end of the drive shaft, so it can take a lot of leverage to break the bell housing loose from the drive shaft. Mine came off quite easily.

You can read about how I do this work here:

• 33 BMW 1977 R100RS Remove Drive Shaft & Swing Arm Bearings

Here are a couple pictures from the write-up.

Drive Shaft Bell Housing Nut

Cycle Works Drive Shaft Bell Housing Removal Tool

Final Assembly of Cycle Works Drive Shaft Bell Housing Removal Tool

Drive Shaft Removed From Swing Arm

I replaced the timing chain, crankshaft sprocket and nose bearing and the three oil seals in the timing chest cover. You can read about this work here:

• 11 BMW 1977 R100RS Replace Timing Chain, Crankshaft Timing Gear & Nose Bearing

The procedure for the 1977 R100RS is the same as the 1975 R75/6 as no major changes in these components was made. I link to the appropriate R75/6 procedures and show differences I found in the R100RS as appropriate.

I did this work in conjunction with replacing the major engine electrical componets. You can read about that work here.

• 12 BMW 1977 R100RS Install Dyna III Electronic Ignition-Refurbish Automatic Timing Unit (ATU)
• 12 BMW 1977 R100RS Refurbish Starter Motor
• 12 BMW 1977 R100RS Replace Engine Electrical Components

Here are a few pictures and videos from the write-up.

Timing Chest Cover Exposed with Cover Puller on Crankshaft Nose

Tachometer Drive Shaft Coming Loose

Timing Chain After Using Bolt Cutter

Dial Indicator Mounted To Check Cam Nose Run Out

VIDEO: Checking Camshaft Nose Runout

Timing Marks When Sprockets Are One Tooth Out of Alignment

Timing Chest Cover Installed

I’ve been making good progress on this project. I’ve finally finished writing up the major engine electrical component replacement and refurbishing the starter motor. You can find this material here.

• 12 BMW 1977 R100RS Replace Engine Electrical Components
• 12 BMW 1977 R100RS Install Dyna III Electronic Ignition-Refurbish Automatic Timing Unit (ATU)
• 12 BMW 1977 R100RS Refurbish Starter Motor

Where the procedure is similar or identical to work I’ve done on other bikes, I link to the existing write-ups and document the condition I found on this bike.

The body work should be back from the painter soon and the hard bits got dropped off for powder coating Tuesday. The clutch was shipped to Southland Clutch yesterday. I’ve got at least one source for anodizing the brake calipers. So a lot of the “outsourced” work is in progress.

Here are a couple pictures from these write-ups.

Engine Electrical Components

Wires on Back of Diode Board

Unsoldering 3-Phase Wires from Terminal Block

New EME Stator

Diode Board, Alternator and Wiring Installed

Dyna III Electronic Ignition

Points Housing Full of Crud

ATU is Rusty

ATU Main Components Disassembled

Old Advance Springs Installed on Cam Plate Pins to Limit Full Advance

New Dyna III Sleeve and Pickup Plate Installed in Points Housing

Starter Motor

Rusty Starter Motor with Cob Webs

Cracked Insulation on (+) Battery Cable; “Red” Wire Wrapped with Electrical Tape

Field Coil Housing Removed Showing Armature

Brush & Coil Spring Detail in Brush Holder

Painted Starter Motor

Due to a lot of cracks in the top middle fairing panel that surrounds the headlight and the fact the upper fairing bracket had both tabs broken that secure the strap that bolts to the steering head, I wanted to check the frame to see if it is straight. I borrowed a frame jig from a long time BMW mechanic who is now retired and used it to see what’s up.  The good news is the frame is straight “enough” for my purposes. 🙂

You can read about how I did this work here.

• 46 1977 BMW R100RS Check If Frame Is Bent

Duane Auscherman has a nice page that describes a technique you can use to check if a frame is bent and it does not require this jig. I included a link to his web page in the above write-up.

Here are a few pictures of the frame jig in use.

Frame Jig

Jig Orientation & Steering Head Bar

Frame Jig Installed in Steering Head

Swing Arm Locating Pin Inserted In Rear of Jig

Swing Arm Pin Centered In Right Swing Arm Bushing

Swing Arm Locating Pin Off Center in Left Swing Arm Bushing By 2-4 mm GOOD ENOUGH 🙂