1977 BMW R100RS Refinishing and Rebuilding Master Cylinder and Calipets

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

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

As Purchased with Later Snowflake Wheels

Calipers Showing Anodized Blue Fading

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 ūüôā ) 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

Refinished and Rebuilt Calipers Installed in Fork Lowers

Speigler Braided Steel & Rocky Point Cycle Stainless Steel Caliper Line

Speigler Braided Steel & Rocky Point Cycle Stainless Steel Caliper Line

Refinished & Rebuilt Master Cylinder Mounted on Spine Tube

Refinished & Rebuilt Master Cylinder Mounted on Spine Tube

1977 BMW R100RS Replace and Adjust Wheel Bearings

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:

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

“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

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

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

Rear Wheel Ready To Roll

Front Wheel Ready to Roll

Front Wheel Ready to Roll

1983 R100RS Repair Instrument Circuit Board Foil

One indicator bulb in the instrument housing was not lighting. I pulled the instrument cluster out and tested the bulb which was good. However the foil trace that goes on the tab inside the hole in the circuit board the bulb holder plugs into had broken.

Tab Bulb Connector Lead Touches-Copper Foil Missing

The Tab The Bulb Holder Lead Touches-Copper Foil Is Missing

I used some copper foil to make a repair and I documented how I did it here.

The same technique can be used to repair any of these boards when a cracked or broken foil trace causes intermittent or complete bulb failure bulb. But sometimes the circuit board is broken, badly corroded and it isn’t salvageable.

BMW no longer sells the circuit board but you can find used ones for sale on eBay and some are in good condition. However someone took the time and effort to design a replacement light housing and circuit board that uses LED lights instead of the original incandescent bulbs. For a badly damaged circuit board where the simple fix I made¬†is insufficient, these replacement boards will likely do the trick. I’ve not had occasion to install one of these, but you will find information about them here:

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 Replace Rocker Arm Needle Bearings, Remove & Inspect Valves

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.

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

Left Exhaust Rocket-Bottom Rocker Needle Bearing Cage Damaged

Left Exhaust Rocket-Bottom Rocker Needle Bearing Cage Damaged

Left Exhaust Lower Rocker-Recovered Needle Bearings and Cage Pieces

Left Exhaust Lower Rocker-Recovered Needle Bearings, Some Broken, and Pieces of The Cage Lip (Tooth Pick For Scale)

Rocker Arm Bearings in Bottom of Oil Pan

Rocker Arm Bearings in Bottom of Oil Pan

Left Exhaust Top Rocker Needle Bearings-Note Gap Between Needles at Bottom Which is Normal

Left Exhaust Top Rocker Needle Bearings-Note Gap Between Needles at Bottom Which is Normal

Ready to Drive Bearing Cages Out of Rocker Arm

Ready to Drive Bearing Cages Out of Rocker Arm

Valve Spring Compressor

Valve Spring Compressor

Valve Spring Compressor Ready To Remove Valve

Valve Spring Compressor Ready To Remove Valve

Portion of Valve Face is 1 mm Thick

Portion of Valve Face is 1 mm Thick

Portion of Valve Face at 0.5 mm

Portion of Valve Face is 0.5 mm