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:
- 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
Brook, kudos on a really nice set of photos and writeup with links to previous work showing how doable the work is! Simple by design indeed!
Hi Domingo,
Thanks for the kind words.
Best.
Brook.
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.