1983 BMW R100RS Install Engine Top End

The engine came with the stock 8.2:1 compression pistons. But the early RS motors came with high compression 9.5:1 pistons. The bike has 83,000+ miles on it. So I decided to install new high compression pistons. Tom Cutter at Rubber Chicken Racing Garage, told me due to the very tight piston clearances in the Nikasil cylinders and the amount of variation in piston diameter with the new pistons, the best way to proceed is to replate the cylinders with Nikasil and hone them to match the pistons to ensure proper clearance. So, I send him the new pistons, rings, wrist pins and old cylinders for this work to be done. I also had him vapor hone the cylinders to refinish them to the factory patina.

Refinished Cylinders with New Push Rod Tubes

Refinished Cylinders with New Push Rod Tubes

The other work needed was to the heads. When I tested them, the valves were leaking. So I sent the heads to Randy Long, at Long’s Mechanical Services, who is a well respected head rebuilder, for his opinion. We decided to replace the exhaust valves, all the exhaust guides, springs and keepers. I had him machine the heads for dual plugs. I have dual plug heads on two airhead bikes and I like the improved gas mileage. Randy milled the valve cover mating surfaces so they are flat and bead blasted the heads so they look brand new.

Randy Long's Rebuilt Heads

Randy Long’s Rebuilt Heads

Rebuilt Head with New Exhaust Valve and Dual Plug Conversion

Rebuilt Head with New Exhaust Valve and Dual Plug Conversion (Note Two Spark Plug Holes

Here is what I ended up with. The red tape indicates things I need to do before first engine start: install new spark plugs and put oil in the engine. The rags protect the heads from getting anything inside from the intake and exhaust ports.

Red Tape Means Not Ready Yet

Red Tape Means Not Ready Yet

All Done

All Done

Here is written documentation of the procedure:

And here is a video of the procedure.

VIDEO: 1983 BMW R100RS Install Engine Top End

8 thoughts on “1983 BMW R100RS Install Engine Top End

  1. Brook,
    Your timing is perfect. I am just about to start the same operation as soon as some parts arrive, so thank you for your tutorial. Also, I like your “red tape” approach alerting one to critical items that need completing. Brillant!

    Best regards,

  2. Very detailed and informative video. I always learn some thing when I watch other people assemble anything on YouTube. I have one comment though. I have been instructed to beware of the lateral play of the rocker arms between the two sliding blocks on either side of the arms. This can cause some valve train noise if excessive. The blocks should be fairly tight against the rocker arms before tightening the head nuts on top of them. Thank you so much for all of your efforts.

    • Kit, you are correct about that. I find if I pinch them tightly between my fingers when I tighten the rocker nuts, the rockers don’t bounce up and down between the pillow blocks. Thanks for calling that out.

  3. Great video,bookmarked and saved for later. Wish I’d seen earlier. Recently got my 81 R65 project bike running again after rebuilding carbs, refurb’ed left cylinder head and new valves, new gaskets etc. among other projects on the bike. Bike is running good after a long 10+ year nap. Someday I will need to remove the cylinders and do the full Monte but will enjoy it running for a while and work on getting it titled (purchased without) for now, Thanks

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