1973 R75/5 Rebuild: Remove/Install Flywheel, Replace Rear Main Seal, Oil Pump Cover and O-ring

I posted a new page on removing the flywheel, replacing the rear main seal, oil pump cover and cover o-ring and installing the flywheel. This also covers a repair to a leak I found in one of the crankshaft flywheel bolt holes.

The work I did was guided by a lot of advice and web content shared by others who have gone before me.  I’d like to acknowledge folks who regularly participate on the BMW Airhead forum on Micapeak.  In particular, Tom Cutter who runs  Rubber Chicken Racing Garage and Bob (Snowbum) Fleischer who has a great technical library on all things BMW motorcycles, answered questions I posted on the Micapeak forum and in personal Email and phone conversations.  I also used web materials posted on  Duane Ausherman’s site.

Here a few pictures from the write up.

Make-do Engine Stand

Make-do Engine Stand

10mm Long Bolt in Alternator to Block Crackshaft

10mm Long Bolt in Alternator to Block Crackshaft

Flywheel Bolts out And Oil Leaking

Flywheel Bolts Out And Oil Leaking From Crankshaft Hole

Removing Oil Pump Cover with Impact Driver

Removing Oil Pump Cover with Impact Driver

Tightening Bolt to Pull Rear Main Seal

Tightening Bolt to Pull Rear Main Seal

Heated to 220 F

Heating Flywheel Bolt Circle to 220 F Prior To Installation

6 thoughts on “1973 R75/5 Rebuild: Remove/Install Flywheel, Replace Rear Main Seal, Oil Pump Cover and O-ring

  1. Brook,
    Thanks for the great documentation of your procedure, awesome!
    My bike is a ’76 R90S, and I am just assembling the parts to do a main seal replacement after having the transmission out for a rebuild, so I am learning alot from your experience. I do have a couple of questions on the procedure you used in putting the new main seal in. It looks like you fitted the main seal to the flywheel hub first to get it to fit properly. Did you then take the main seal off the flywheel and fit it to the crank? Then press the flywheel back into the main seal as you were re-attaching the flywheel to the crank?
    Thanks,
    Marty Nelson
    Seattle

    • Marty,

      Thanks for reading and posting the question. I did remove the new main seal off the flywheel hub after forming the lip. After I installed the seal with the Cycle Works tool, I mounted the flywheel on the crankshaft hub and pushed it onto the crank past the seal.

      I just updated the the write up to make that clear. Thanks for helping make the description more explicit.

      Best.
      Brook.

  2. Outstanding writeups! I’m thick in the middle of a resto of a ’71 R75 and I’m going through your articles with great interest. Thanks for the effort!

    J.

  3. Brook,

    Great write-up on the flywheel R & R. I’m there now with my rebuild. Yes, I did block the front of the crank before removing – thanks for the heads-up.

    Couple questions…would you know if the oil pump cover plate has to be replaced when using the red o-ring or could I use a red one on my old cover plate with the countersunk screws? The red one (11 41 1 335 895) is the only one listed at Max BMW & says it fits 1970 – 1995.

    Rear Main Seal…the Teflon seal (11 11 1 338 342) is the only one listed at Max BMW, but Motobins lists a second PN (11 11 1 337 674) and the description states…

    “This is a good seal if your bike is mainly used in the summer and put away for the winter as it will hold up to being layed up for periods on time better than the 40100 (11 11 1 338 342) seal.”

    This type of usage is much more in line with the way I’ll be using the bike. Do you have any thoughts on the optional seal? Any problems with leakage using the Teflon seal?

    Thanks for your time,

    Joe in St Louis

    • Hi Joe,

      On the red o-ring question, I don’t know if the groove in the old cover is the same as the groove in the new cover. I opted to replace my cover for the convenience of bolts that are easy to remove compared to phillips screws in the older cover.

      On the Moto-bins seal, I have no experience with it nor am I knowledgeable about what the difference is between the stock BMW version and the Moto-bins optional version.

      All the best on your project.

      Best.
      Brook.

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