1977 BMW R100RS Remove, Refurbish, Install Clutch and Replace Rear Main Seal & Oil Pump Cover O-ring

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:

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:

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:

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

M6 x 10 mm Bolt In Alternator Rotor Allen Head Bolt

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

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

Clutch Ready to Remove

Ready To Remove Clutch

Accumulated Crud on Transmission Shelf

Accumulated Crud on Transmission Shelf

Clutch Removal Bolts-Nut Distance From Bolt Head

Clutch Removal Bolts-Nut Distance From Bolt Head

Clutch Alignment Marks

Clutch Alignment Marks

Diaphragm Spring with Streaks of Lubricant :-(

Diaphragm Spring with Streaks of Lubricant 🙁

New Diaphragm Spring Height & Partial Part Number (Right)

New Diaphragm Spring Height & Partial Part Number (Right)

Added Flywheel Index Marks

Added Flywheel Index Marks

Oil Leak From Crankshaft Bolt Hole (1:00)

Oil Leak From Crankshaft Bolt Hole (1:00)

Groove Cut Into Flywheel By Rear Main Crankshaft Seal

Groove Cut Into Flywheel By Rear Main Crankshaft Seal

Starting To Clean Bell Housing

Starting To Clean Bell Housing

Bell Housing After Cleaning

Bell Housing After Cleaning

Timing Marks Painted for Visibility

Timing Marks Painted for Visibility

Flywheel Timing Marks with added 25 Degrees BTDC Mark

Flywheel Timing Marks with added 25 Degrees BTDC Mark

New Flywheel Hub O-ring

New Flywheel Hub O-ring

Engine Strapped To Work Bench Before Torquing Flywheel Bolts

Engine Strapped To Work Bench Before Torquing Flywheel Bolts

4 thoughts on “1977 BMW R100RS Remove, Refurbish, Install Clutch and Replace Rear Main Seal & Oil Pump Cover O-ring

  1. Hi Mr Reams
    I require some advice.
    I just bought a 1977 Bmw R100 rs . I always wanted a R100.
    The most unfortunate thing occurred on my first ride on the motorcycle,
    The motorcycle just lost power and came to a holt. I had it salvaged to a workshop. I was informed I sustained a bearing knock to the engine.

    My question would be will this repairable or is it easier to find a replacement engine for my motorcycle?

    Kind regards.
    Denzil (South Africa)

    • Hi Denzil,

      I am sorry to hear about the problem you have with your R100RS. A rod bearing knock can be repaired by removing the crankshaft, machining the rod bearing surface and installing new rod bearing shells that are thicker. I don’t know if there is other damage to the engine. It will not take the workshop long to remove the heads, cylinders and pistons and inspect them for any damage. I would try to repair first. If the estimated price is very high, you can look for a used R100 engine.

      I hope this helps.

      Best.
      Brook Reams.

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