…cleaning, inspecting, and servicing the throwout assembly on ’74 to ’84 airheads every 10K. Would someone be willing to describe this process in enough detail so that I would have half a chance of performing this myself successfully?
Sure… The reason I suggest doing this, is due to the nature of the layout of the rollers in the bearing. Before the ’74’s (/5 and earlier), BMW used a ball bearing throw-out assembly. They went back to this after 1984. If you referrence a price list, you will see that the ’74 to’84 roller set up is a LOT cheaper. The rollors are laid out radially in a circle.This insure that as the rollers attempt to roll, one end will go faster than the other and will scrape on the two “thrust pieces” on each side.
The bearings do fail (usually indicated by a sudden need to take up slack in the clutch cable). Now, the failed bearing, the two thrust pieces and the clutch thrust rod are turning as a unit. The clutch end of the thrust rod can bore into the forward pressure plate of the clutch assembly. Surprisingly, the bike can still be operated while this is going on, with the rider noting strange shifting and odd clutch noises. This happens often enough that I carry a spare set up as insurance for my wife’s ’78 R100/7, when we tour. (I have, of course, the vastly superior /5)
OK, how to check a new-to-you bike/10K service interval. Detach the clutch cable at the throw-out arm. Clean up the area , as there usually is a lot of road grit on the back of the gear-box. There is a C-clip that locks the throwout pivot rod to the two cast aluminium “ears” of the rear gearbox cover. CAREFULLY remove this (this is one of those parts that disappear into the ozone/grass/gravel/your pants cuff very easily). Pull out the pivot pin with a pair of pliers. The throw-out arm should now come away in your hand easily. I use a magnet-on-a-stick to draw out the rear thrust piece, the bearing and the forward thrust piece.The thrust rod runs through the input shaft of the gear box and will stay there – you have to remove the gearbox to get it out. Paper towels and carb cleaner are good to clean up all these pieces and the place they came from.
Now that all is clean and dry, examine: The thrust pieces should be smooth and polished, with no pitting. The bearing should be intact, with no chewed up or broken rollers. I have dressed out minor wear on the thrust pieces with fine crocus cloth and a plate glass surface but I understand that the wear surfaces are surface hardened, so any serious material removal would result in a soft bearing surface. On the ones I’ve cleaned up, there haven’t been any subsequent problems. I would be tempted to replace any worn parts and keep the worn parts under the seat as a get-you-home kit. If everything is clean and only showing nowmal polishing/wear; replace the parts. Put a dab (1cc or so) of grease in the cup of the throwout arm where it pushes the thrust rod. If the little rubber protector of this area is torn/rock hard/gone; replace that too. I put a few drops of new gear oil on the bearing as it goes back into the back of the gearbox. A coating of grease goes on the pivot pin as it goes back. Give a shot of grease to the zerk fitting on the throw-out lever. Hook up the cable and adjust, using the 10mm bolt, with 13mm lock nut, on the rear of the throw-out lever. That’s it.
After doing all this, I would suggest cleaning and greasing the OTHER end of the clutch cable, as well, at the hand lever (this is part of a 5K and 10K service). Hope this covers it for you.
