1983 BMW R100RS Remove Push Rod Tubes & Cylinder Studs

When BMW introduced the Nikasil cylinders in the US in the 1981 model year, they came with the 8.2:1 low compression pistons to help meet EPA requirements. So, my 1983 R100RS has low compression pistons. But, in Europe, BMW provided 9.5:1 pistons and rings for use in the Nikasil cylinders and they are still available.

The higher compression makes a useful difference in torque and horsepower:

  • The 8.2:1 compression pistons produce 53-Ft-Lb and the 9.5:1 compression produces 56 Ft-Lb and, or about +5% for the higher compression.
  • The 8.2:1 compression pistons produce 66 Hp and the 9.5:1 compression produces 70 Hp and or about +6% for the higher compression.

I intend to use this bike for two up touring and it has over 80,000 miles on it. So I am going to install 9.5:1 pistons sized for the “B” sized cylinders I have (part# 11 25 1 337 175) to get a useful boost in torque and horsepower.

New 9.5:1 Piston Kit For "B" Size Cylinder

New 9.5:1 “B” Size Piston Kit For “B” Size Cylinder

New 9.5:1 Piston Kit Contents

New Piston Kit Contents-“B” Size, 9.5:1 Piston (93.97 mm)

For the best fit and an oil tight motor, the recommendation from Tom Cutter at Rubber Chicken Racing Garage is to replate the Nikasil inside the cylinders and then hone it to get the proper clearance that matches the actual pistons. There is some variability in the pistons and this approach mates the cylinder dimensions to the piston dimensions for a tight seal.

Here is the link to the write-up of the procedure.

And here is a link to a short video I made of the procedure. It shows the “Risky” way to remove the push rod tubes–and the unintended consequence–and a “Safer” way to do it.

VIDEO: 1983 BMW R100RS Remove Push Rod Tubes & Cylinder Studs

1983 BMW R100RS How To Disassemble Down to the Frame

I got the engine out of the frame yesterday so I’m finished with disassembly (small cheer can be heard).

I wrote a document that covers the complete disassembly procedure in the order I did the work.

This may be helpful to you if you are doing a frame off rebuild/restore, or you need to know how to remove various subsystems. The bike, with the exception of the body work, fits into a reasonably small pile of boxes … sort of a boxed, boxer if you will :-).

Engine Removed

Engine Removed

Naked Frame

Naked Frame

A Boxed "Boxer" :-)

A Boxed “Boxer” 🙂

Onward. But first I’m giving “Grover”, the 1973 R75/5 some well deserved attention.

1983 BMW R100 RS Remove Exhaust, Transmission and Engine Top End

I’ve finished removing more on the bike and have posted documents about how I did the work here.

I also made a short video showing how to remove the top end.

VIDEO: 1983 BMW R100RS Remove Engine Top End

At this point, disassembly is almost done, and the real work begins; repair, rebuild and refinishing all the components of the bike.

1983 BMW R100RS Remove Carburetors & Air Box

Earlier, when I first got the bike, I rebuilt the carburetors and removed the “Pulse Air” system from the air box. You can read about how I did that here.

The following includes similar information to what’s in the documents above, but here I’ve simplified it to just removing these components as part of the complete disassembly of the bike. You can read about how to do that here.

Left Carburetor Attached to Air Box

Left Carburetor Attached to Air Box

Air Box Removed

Air Box Removed

1983 BMW R100RS Remove Rear Wheel, Rear Drive, Shocks & Swing Arm

I’ve completed the disassembly of the rear end of this bike. Previously I removed the rear fender, tail light and turn signal assemblies. You can read about that work here:

Here is where I started.

Front End Removed & Ready To Start On The Rear End

Front End Removed & Ready To Start On The Rear End

And here is what the bike looks like now.

Bike After Rear End Removed

Bike After Rear End Removed

Next up is removing the transmission, clutch throw-out arm and rod assembly and the foot shifter mechanism.