I’ve posted a series of write-ups that cover rebuilding the front end of this bike.  You can find them here:

• 31 BMW 1977 R100RS Remove Front Forks, Handle Bars, Steering Stem, Fork Lock
• 31 BMW 1977 R100RS Replace Steering Head Bearings, Rebuild Front Forks
• 31 BMW 1977 R100RS Install Steering Stem, Front Forks and Toaster Tan Top Brace
• 34 BMW 1977 R100RS Rebuild and Restore Front Disk Brakes & Master Cylinder
• 36 BMW 1977 R100RS Wheel Bearings-Replace & Adjust Preload

These write-ups cover disassembly of the handlebars, forks, steering stem, steering damper and fork lock, rebuilding and restoring the wheels, wheel bearings, fork damper rods, fork sliders, steering stem bearings, fork lock, steering damper and installation of a new Toaster Tan top brace and steering stem “acorn” nut.

I also used Speigler braided steel brake hoses, stainless steel caliper brake lines from Rocky Point Cycle.

Here is what I started with.

Torn Top Plate of Left Perch

Fork Lock

Front Wheel Left Side of Hub Showing Corrosion

Master Cylinder Grunge and Rust

Original Caliper is Faded, Axle is Rusty, Fork Lowers Chipped

Friction Material Is Separating from Steel Backing Plate

Exterior Fading of Caliper Anodizing

Telefix Fork Brace Needs Refinishing

Stock Fork Brace-Fender Mount

And here is what I ended up with.

Fork Lock Installed in Powder Coated Frame

Powder Coated Front Wheel with New Wheel Bearings Ready to Roll

Repaired & Painted Control Housings

Rebuilt and Refinished Master Cylinder Mounted on Spine Tube

Toaster Tan Top Plate & Steering Stem “Acorn” Nut Mounted

Toaster Tan Top Plate

Stock Fork-Fender Brace Mounted on Rebuilt Forks

Speigler Braided Steel & Rocky Point Cycle Stainless Aluminum Caliper Line

I refinished and rebuilt the master cylinder and calipers. You can read about how I did the work here:

• 34 BMW 1977 R100RS Rebuild and Restore Front Disk Brakes & Master Cylinder

This bike had the blue front calipers and the ATE front disk brakes with the drum rear leading and trailing shoe brakes. Originally, the wheels were wire spoke but a previous owner upgraded them to the later snowflake wheels.

As Purchased with Later Snowflake Wheels

Blue Anodizing on Calipers Has Faded

I rebuilt the two front calipers, the master cylinder and replaced the rear brake shoes. The blue anodized calipers had faded so I had them anodized, but this was a dismal failure. Either the shop who did the work botched it or it’s not so easy to anodize old parts. I found a paint that replicates blue anodizing. I stripped the botched anodizing and painted them. I like the result.

I replaced the lower steel brake line that goes between the caliper and the union that is inserted into the lower front fairing with stainless steel lines from Rocky Point Cycle. I replaced the rubber lines with braided steel lines with a translucent blue cover and chrome unions from Spiegler Performance Parts.

Here is the finished product. When the fairing comes back from the paint shop (soon, real soon now 🙂 ) I’ll connect the upper steel lines to the braided steel line through the bushing in the top center fairing panel.

Refinished and Rebuilt Calipers Installed in Fork Lowers

Speigler Braided Steel & Rocky Point Cycle Stainless Steel Caliper Line

Refinished & Rebuilt Master Cylinder Mounted on Spine Tube

A lot has been written about the procedure  to correctly set the wheel bearing preload. There is more than on technique for determining the correct preload. And wheel bearings can fail if the preload is set too low or too high. For that reason, I’ve put off setting the preload for many years and had a shop or Woody’s Wheel Works do it. But on this project, working on the wheel bearings was one of the items I had on my “Learn New Skills” list, so, now’s the time.

You can read about how I did this work here:

• 36 BMW 1977 R100RS Wheel Bearings-Replace & Adjust Preload

This bike does not have the original spoke wheels. Instead it has the cast aluminum alloy “snowflake” wheels that came latter. The rear snowflake has a drum brake while later versions of the snowflake rear wheel have a rear disk brake on the left side.

“10 Foot” View Showing Later Snowflake Wheels Installed

It seems that airhead wheels are a component that BMW changed a lot over the life of the airhead bikes. Further, parts fiche diagrams are notoriously confusing and frequently show incorrect parts. As I tried to get solid information about my wheels, one sage, long time wrench advised me to just inspect the parts that are there and replace what’s worn.

That said, these wheels had parts that took me some time to figure out. First, the snowflake drum rear wheels were only available with an aluminum hub in 1978. Later versions had a steel sleeve in the hub that the rear wheel bearing outer races fit into. This is an improvement as the aluminum hub to steel race interference fit was prone to allowing the race to spin in the aluminum hub which leads to a mess not to mention it can lock up the rear of the bike if the bearing seizes to the axle.

My drum snowflake rear hub has a steel sleeve as shown below. The inner edge of the hub is magnetic and you can see the line between the inner sleeve and the outer aluminum of the hub.

Rear Wheel Hub Has an Inner Steel Sleeve

I used the spring scale method to determine the preload. This is a simple technique that is precise enough.

Pull Gauge and String Wrapped on Axle Spacer Tube

I had the wheels powder coated as well.  Here they are with the new wheel bearings installed and adjusted.

Rear Wheel Ready To Roll

Front Wheel Ready to Roll

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.

• 13 BMW R100RS Rebuild & Refinish Bing Type 94/40 Carburetors

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.

• 13 BMW 1973 R75/5 Rebuild Bing Carburetors & Karcoma Petcocks
• 13 BMW 1975 R75/6: Silver Ghost Restoration-Part 17 Carburetor Rebuild, The Good, The Bad & The Ugly
• 13 BMW 1983 R100RS Rebuild Bing Carburetors & Karcoma Petcocks

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 Inside

Refinished Back

Refinished Front

Refinished Top with Added Rondel