1983 BMW R100RS Remove Drive Shaft

I’m going to powder coat the swing arm so I need to remove the drive shaft. BMW used two different drive shaft designs on the airheads changing the design in the 1981 model year. This 1983 RS has the second design drive shaft.

Pre-1981 Drive Shaft and Swing Arm

Pre-1981 Drive Shaft Components and Swing Arm

Pre-1981 Driveshaft With Tapered End That Shrink Fits Into Bell Coupling

Pre-1981 Drive Shaft With Tapered End That Shrink Fits Into Bell Coupling

Drive Shaft Assembly Components

1981+ Drive Shaft Assembly Components

1981+ Drive Shaft Torsional Shock Absorption Assembly

1981+ Drive Shaft Torsional Shock Absorption Assembly

Cycle Works makes tools to remove the drive shaft. So they have two different tools.

Cycle Works Driveshaft Removal Tool 1955-1980

Pre-1981 Cycle Works Drive Shaft Bell Housing Removal Tool

Pre-1981 Cycle Works Drive Shaft Bell Housing Removal Tool

Here is a link to the description of this tool.

Cycle Works Driveshaft Spring Compressor Tool 1981+

This the tool used to compress the drive shaft spring so I can remove the snap ring that secures large yoke with the bell coupling from the drive shaft.

1981+ Cycle Works Drive Shaft Removal Tool Components

1981+ Cycle Works Drive Shaft Removal Tool Components

Here is a link to the tool description.

I documented how I did this work here:

And, I made a video showing assembly of the Cycle Works drive shaft spring compressor tool and how I used it to remove the drive shaft.

1983 BMW R100RS Remove Valves and Inspect

I’m going to have the heads on this project dual-plugged. Before I sent them to Randy Long who does this work, and more, I did an inspection of the valves to see what I could learn. I documented this work here:

It includes this short video.

VIDEO: 1983 BMW R100RS Remove Valves and Inspect

Randy Long is an excellent resource if you need work done on your heads, valves or seats. He doesn’t have a web site, so here is his contact information:

Randy Long
Long’s Mechanical Services
74 Risbon Rd
Honey Brook, PA 19344-1754
(610) 286-5870

 

1983 BMW R100RS Remove Connecting Rods

I’m going to have the Nikasil cylinders on this bike replated and honed to match the new 9.5:1 pistons I’m going to install in this build. I’ve learned from a well versed airhead mechanic, Tom Cutter, at Rubber Chicken Racing Garage, that the connecting rods are subject to deformation over time such that the distance between the hole centers of the big end and little end of the rod becomes a bit longer than when new. It’s worth having them checked and the flat of the connecting rod cap machined to achieve the design distance between the hole centers. This is not very expensive and ought to reduce wear and tear on the wrist pin and crank shaft throw.

It’s quite straight forward once you have the top end removed as I document in this write-up:

And here is the write-up on removing the connecting rods:

Here is a short video I made showing the tools and the procedure.

VIDEO: 1983 R100RS Remove Connecting Rods

 

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

Musing: Truth and Motorcycles

I think Truth is a slippery concept. Here are three statements commonly held to be true with little debate:

  • 1 + 1 = 2.
  • The sky is blue.
  • What goes up must come down.

The first statement is true as long as there is agreement about the meaning of the symbols “1”, “+” and “2”, and you are talking about counting things. But, it isn’t true if you use it to predict what happens when you add two drops of water together: in that case you end up with only one drop of water.

The second statement is not always true, for example at night, on a cloudy day or if you are standing on the moon. The last statement is not true for the two Voyager space craft which will never return to earth.

These examples are my feeble attempt to show that “context” is very important when you are looking for the truth. Truthfulness exists within a context. You can fall into a “truth trap” if you blindly assume truth in one context is a universal truth for every context.

Since truth exists in a context, you have to look for and understand the context surrounding a statement about the truth and then evaluate if a different context is sufficiently the same before you can can conclude if the statement will be true in the new context. That’s not so easy. I think the ability to judge how similar two contexts are when looking for the truth is one hall mark of “critical thinking”.

Defining a context is not so easy. This is often due to unspoken, or unconscious, assumptions you have which do not apply in a different context. The three true statements I made above all had hidden assumptions about context which leads a casual reader to agree that they are true. It’s very hard to see your assumptions about common experience.

I point this out because when I work on motorcycles there are times when I can’t find the cause of a problem. Every test I try indicates nothing is wrong, but yet, the truth is, something is wrong.

I’ve learned that when I find myself in this situation, it’s time to write down all my assumptions. Often I have to do this more than once because the hard part about assumptions is you don’t recognize you have made them. Then I test every one of them. Every time I have used this meticulous listing of assumptions and testing, I’ve found one that isn’t a valid assumption in the context of the problem.

I hope this helps you solve problems that are too slippery to get a grip on.