1977 BMW R100RS 4400 Mile Status Report

In two months since I completed the build, I’ve ridden the bike 4,400 miles.  I named it “Gonzo” as I like to name my bikes after Muppet characters :-).

Gonzo Starting Mileage On Departure for Pennsylvania

Gonzo Starting Mileage On Departure for Pennsylvania

I rode it to the 40th R100RS anniversary rally in Pennsylvania and back and had a problem with the transmission about 350 miles from the rally that required me to stop riding until it was fixed. That work was done by Tom Cutter of Rubber Chicken Racing Garage and I completed the ride home only one day late.

I documented the issues, corrections and updates I made from the first engine start through the end of my ride back from Pennsylvania here.

There are still some items to work on, but overall, the bike is running well.

Ending Mileage After 3,300 Mile Trip to Pennsylvania and Back

Ending Mileage After 3,300 Mile Trip to Pennsylvania and Back

1977 BMW R100RS Bing Type 94/40 Carburetor Rebuild-Refinish

This is the fourth set of Bing CV carburetors I’ve completely rebuilt. This is the link to the current work on the 1977 R100RS that uses the Bing 94/40 model of carburetors and specifically the 103-104 series used on the 1977 “CFO” engine version of the R100RS.

The previous rebuilds include the smaller 64/32 series used on the R75 series /5, /6 and /7, and the R90/6 bikes and the larger 94/40 series used on the later R100 model bikes. I documented the procedures of the earlier work in the following write-ups.

As is often the case, I found the o-rings were hard and brittle and in one instance I found two o-rings on the idle fuel jet! The internals were pretty clean so I someone cleaned the carburetors and for some reason added an o-ring instead of replacing it on the idle fuel jet.

I decided to shoot some short videos to demonstrate how I understand the way the Bing CV carburetors work. Each video covers one of the four major functions, or circuits, used in these carburetors. The operation of the model 64 and 94 CV carburetors is the same.

Constant Velocity Circuit Operation

Here is a short video showing how the constant velocity circuit works.

Main + Needle Jet Circuit Operation

Here is a short video showing how these components work in the main+needle jet circuit.

Enriching Circuit Operation

Here is a short video showing how the enriching circuit works.

Idle Circuit Operation

Here is a short video showing how the idle circuit works.

Here are some pictures of the completed carburetors.

Refinished Outside

Refinished Outside

Refinished Inside

Refinished Inside

Refinished Back

Refinished Back

Refinished Front

Refinished Front

Refinished Top with Added Rondel

Refinished Top with Added Rondel

1977 BMW R100RS Project: Remove & Repair Bodywork

I wrote up how I removed all the body work on this bike. I discovered a broken upper fairing bracket that was held on with only a hose clamp. There was a broken plastic boss with a threaded insert and numerous cracks and other damage to the fairing panels and side covers. I repaired all of them except for the top center panel that goes around the headlight. The damage was significant with a multitude of hairline cracks and I opted to buy a used panel rather than risk cracks showing up in the paint work after I tried to repair it.

Here are links to the write-ups.

I’m ready to start removing the forks and working my way towards the rear as I strip it down to the frame. Then I can see what other surprises are in store 🙂

Here are a couple pictures from the write-ups.

Screen Damage So I Will Replace It

Windscreen Damage

Drill Bit and Hammer Removing Center Pin of Windscreen Rivet

Tapping Drill Bit with Plastic Hammer to Drive Center Pin Out of Windscreen Rivet

Windscreen Removed

Windscreen Removed

Carefully Drilling Inside of Dash Rivet

Carefully Drilling Inside of Dash Rivet

Dash Removed From Fairing Panels

Dash Removed From Fairing Panels

Broken Upper Fairing Bracket Steering Stem Mount

Broken Upper Fairing Bracket Steering Stem Mount

Fairing Panels Removed

Fairing Panels Removed

Headlight Panel Badly Broken

Headlight Panel Badly Broken

Headlight Panel Lower Right Corner Badly Damaged

Headlight Panel Lower Right Corner Badly Damaged

Upper Side Panel with Large Crack

Top Left Side Panel with Large Crack

Top Side Panel Cracks Routed Out with Dremel Tool

Top Left Side Panel Cracks Routed Out with Dremel Tool

Top Side Panel Plast-aid Repair

Top Left Side Panel After Plast-aid Repair and Sanding

Bottom Side Panel Repair to Brass Insert Boss

Bottom Right Side Panel Repair to Brass Insert Boss

Bottom Side Panel Brass Insert Final Hole Size

Brass Insert Final Hole Size-5/16″

Bottom Side Panel Brass Insert Test

Testing Integrity of Boss & Brass Insert Repair

1975 BMW R75/6: Rebuilding Master Cylinder & Caliper

This bike uses a single ATE 38 mm caliper (as in the size of the piston inside the caliper, not the size of the caliper shell). In 1976 the ATE caliper was changed to a 40 mm model to improve braking. There was also a change to the master cylinder mounting system resulting in a single hole in the brake fluid reservoir that mounts on top of the master cylinder. Other than these small changes, the work I did applies to all the /5, /6 and /7 models of the ATE caliper and under-the-tank master cylinder.

You can read about how to do this work here:

I had occasion to work on both my 1975 R75/6 and someone else’s 1976 R75/6 at the same time, so there are some pictures of the markings on the 40 mm caliper and the different mounting systems (two hole and one hole) of the brake fluid reservoir.

Some pictures from this write-up are below.

Master Cylinder & Fluid Reservoir Mount Under Gas Tank

Master Cylinder & Fluid Reservoir Mount Under Gas Tank. Note the Evidence of Brake Fluid Leak.

Earlier Style Master Cylinder Fluid Reservoir-Two Holes With Mounting Bracket

Earlier Style Master Cylinder Fluid Reservoir-Two Holes With Mounting Bracket

Later Style Master Cylinder Reservoir-Single Hole With Threaded Sleeve

Later Style Master Cylinder Reservoir-Single Hole With Threaded Sleeve

Earler Two Hole Master Cylinder

Earler Two Hole Master Cylinder

Master Cylinder Piston Assembly Removed

Master Cylinder Piston Assembly Removed

Removing Top Hat From Master Cylinder Piston

Removing Top Hat From Master Cylinder Piston

Master Cylinder Rebuild Kit Parts

Master Cylinder Rebuild Kit Parts

New Master Cylinder Piston with New Rubber Seals Installed

New Master Cylinder Piston with New Rubber Seals Installed

Master Cylinder Installed on Frame Tube

Master Cylinder Installed on Frame Tube

R75/6 Caliper Seal Kit - Source: MAX BMW

R75/6 Caliper Seal Kit – Source: MAX BMW

Caliper Showing Piston and Dust Seal

Front Face of Piston with Center Hole Surrounded by Rubber Dust Seal

A Blast of Compressed Air Removes Piston

A Blast of Compressed Air Removes Piston

Dust Seal Installed in Large Groove in Piston

Dust Seal Installed in Large Groove in Piston

Pulling O-ring On Eccentric Pin With Pick

Pulling O-ring On Eccentric Pin With Pick

Movable Pad with Flat Face of Pad Pointing to the Front

Movable Pad with Flat Face of Pad Pointing to the Front

Fixed Pad Secure with Wire Clip

Fixed Pad Secure with Wire Clip

Caliper With Painted Metal Line Installed

Caliper With Painted Metal Line Installed

1983 R100RS Rebuild: Diagnose and Replace Failed Neutral Switch

When I bought the bike in January 2015, the neutral bulb didn’t light and the starter motor wouldn’t work unless I pulled the clutch. I need to figure out what is going wrong in the starter circuit and the neutral switch. I wrote up the work I did here including how I diagnosed that the neutral switch failed and how to replace it:
This write-up makes use of some short videos to show what I do. I’m experimenting with how to use video clips to explain things better than just pictures and text can.
There is a longer video at the beginning in which I explain how I use the Haynes wiring diagram and Bob Fleischer’s material to figure out how the neutral and clutch switches work in the starter switch circuit.
I’ve heard fellow Airheads tell me electricity is confusing and a mystery. So I thought maybe showing how I try and figure out how components work from the wiring diagram when I have a problem may be of some value.  Here is a direct link to that video.

Here are the other short videos I shot that are included in the write-up.

Here are a few pictures from the write-up.

Neutral Light Not Lit

Neutral Light Not Lit

Printed Circuit Contacts for Neutral Switch

Printed Circuit Contacts for Neutral Switch

Neutral Bulb Pins on Printed Circuit

Neutral Bulb Pins on Printed Circuit

Neutral Switch with Grunge

Neutral Switch with Grunge

Degreased Bottom of Transmission and Engine Oil  Pan

Degreased Bottom of Transmission and Engine Oil Pan

Prying Out Center Engine Mount Spacer

Prying Out Center Engine Mount Spacer

Old Switch Ready to Remove

Old Switch Ready to Remove

New Neutral Switch and New Washer/Spacer

New Neutral Switch and New Washer/Spacer

New Neutral Switch with Plast-Aid Applied to Prevent Leaks

New Neutral Switch with Plast-Aid Applied to Prevent Leaks

Neutral Light Works Now :-)

Neutral Light Works 🙂