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.

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.

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.

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.

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

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

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.

When I pulled the valve covers off, I found loose needle bearings in the left valve cover when I was tearing down the top end. This is not uncommon as the bearing cage lip wasn’t wide enough on the earlier needle bearing cages and can fracture. So I replaced all the needle bearings in the heads. Each rocker has a pair of needle bearing cages so there are eight total.

I removed the valves and cleaned the heads to see what I could see. Some of the valve faces are worn down and the valve springs are sacked past the minimum. I suspect the exhaust valve seats are original so I’m planning on having new exhaust seats installed. I’ll also replace all the valve guides, springs and the valves so these heads, which are dual-plugged, should last for a long time.

Here is the link to the write-up on how I did this work.

• 11 BMW 1977 R100RS Replace Rocker Needle Bearings, Remove Valves & Inspect

Here are a couple of pictures from the write-up.

I pulled the pistons and connecting rods for inspection. This write-up shows my procedure.

• 11 BMW 1977 R100RS Remove Pistons, Connecting Rods & Inspect

I found a score in one of the rod bearings and I’m going to replace the bearings. The pistons are in good condition, but this bike had the original top end replaced at some point with the later Nikasil cylinders, pistons, rings and gudgeon pin (wrist pin). Unfortunately this reduce the compression from 9.5:1 to about 8.2:1 producing less horsepower and torque. There are European versions of the pistons and rings that provide the original 9.5:1 compression. Hmmm …

Here are a few pictures & a short video or two from the write-up.