I had to replace this switch and decided to document “what wire goes where” inside the headlight shell on the circuit board and to the ignition switch and headlight relay.
I also explain how to map information found in various wiring diagrams to the labeled areas on the circuit board. There are some places where things got confusing for me in going between the various published wiring diagram(s) and the circuit board inside the headlight shell, so I hope this material helps others avoid being confused.
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.
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. Note the Evidence of Brake Fluid Leak.
Earlier Style Master Cylinder Fluid Reservoir-Two Holes With Mounting Bracket
Later Style Master Cylinder Reservoir-Single Hole With Threaded Sleeve
Earler Two Hole Master Cylinder
Master Cylinder Piston Assembly Removed
Removing Top Hat From Master Cylinder Piston
Master Cylinder Rebuild Kit Parts
New Master Cylinder Piston with New Rubber Seals Installed
Master Cylinder Installed on Frame Tube
R75/6 Caliper Seal Kit – Source: MAX BMW
Front Face of Piston with Center Hole Surrounded by Rubber Dust Seal
A Blast of Compressed Air Removes Piston
Dust Seal Installed in Large Groove in Piston
Pulling O-ring On Eccentric Pin With Pick
Movable Pad with Flat Face of Pad Pointing to the Front
Okay, I’ve yet to achieve the first of the 12 steps for recovery: Admitting You Are Powerless Over Your Addiction. I see no problem in adding one more bike to “Brook’s Garage” inventory of BMW Airhead projects. So, I’ve acquired a 1977 BMW R100RS with about 37,300 miles. Yes, I already have the 1983 R100RS bike project, but 1977 is the first year for this innovative machine from BMW. So, getting one has been on my “Lust List” for awhile. Now, it’s in the last remaining storage space next to my car in our garage.
[Hey, maybe if I just sell the car I get 1/2 a garage for more bikes!!! But, I think that way lies divorce, so an even half dozen Beemer Bikes is the limit for “Brook’s Garage”.]
My intent is to complete a frame-up restoration of the bike, but when I start that, I haven’t decided yet. Right now I just began assembling the 1975 R75/6 “S” project bike and the 1983 R100RS was next in line; but that was before the 1977 came home. I’ll see what grabs me when I get the R75/6 “S” out of the shop.
The bike is a “10 foot bike”: It looks nice from 10 feet away :-):
“10 Foot” View
“10 Foot” View
“10 Foot” View
10 Foot View
I’ve ridden it about 75 miles and it certainly shows the value of the 40 mm Bing carburetors and lack of EPA mandated emissions modifications compared to the 1983 R100RS. It has dual plug heads, oil pressure and oil temperature senders and VDO gauges (not installed at present, so I’m not sure the gauges or senders still work), heated grips and is claimed to have the reinforced snowflake wheel installed.
The cosmetics need attention, and we shall see what surprises are inside in due course. Someone did invest in it at one time as evidenced by the modifications, but there are also signs of being parked and ignored as well.
I did the same work on my R75/5 as well which you will find on my site. The main differences between these projects were using Southland Clutch to refurbish the R75/6 clutch where I replaced the clutch on the R75/5 project, and not damaging the rear crankshaft thrust washer this time. 🙂
This is the first time I used Southland Clutch. I am very pleased with their knowledge of airhead clutches, their courteous and prompt service and the quick turn around at a price about one-half the cost of the new parts. I am adding them to my Resources list.
Engine Out of Frame Showing Clutch Compression Ring
Small Bolt in Alternator Nose to Keep Crank From Moving Forward
This bike, a 1975 R75/6, is the first BMW I bought and now has almost 106,000 miles on it. It is the first bike I rode more than 1,000 miles in one day back in 1976 and is the first build project I completed in 2010 and documented here:
I have several projects that I didn’t get to during the build. One of these is replacing the timing chain which I document here with a lot of pictures and detailed step-by-step procedure.
My bike has the duplex, dual row chain, while starting with the /7 series, the timing chain is a single row chain. This procedure should help you replace a /5, /6 or /7 series timing chain, but some of the parts will be different as I note later.
Since I stripped the bike I have the engine out of the frame, but most people will do this work with the engine in the frame. Although it is an option to remove the front wheel and forks to have clear access to the front of the engine, I think the work can be done without removing them.
Before starting this project, I reviewed material available on the Airheads Beemer Club site, www.airheads.org: I believe you can access the links below even if you are not a member, but consider joining this group if you want to contribute to the Airhead culture. I read material on Bob Fleischer’s blog site, and I posted a number of questions to the Micapeak Airheads forum whose members are legend for providing thoughtful advice and encouragement. You should add these resources to your toolkit as they are authoritative with valuable information.
In particular, I want to acknowledge Ron Cichowski, Tom Cutter, Bob Fleischer, Doran Shields, Marten Walkker and Eric Zwicky on the Micapeak Airheads forum for answering my questions. Also, a local Colorado Airhead, Don Wreyford, came by to kibitz and help with the disassembly process. Don has always been generous with his time and knowledge. And, my youngest son, Branden, shown in many of the photos with the electric yellow shirt, helped me on the entire project with wrenching, picture taking, and good ideas and advice when we needed to stop and reconsider what we should do next. He is turning into an accomplished Airhead wrench and lover of Bavarian iron.
Here are a couple pictures from the detailed writeup.
Ready To Start – Front and Top Covers Removed
Alternator Stator and Housing Removed as A Unit
Alternator Rotor Fits on Tapered Crankshaft Nose
Engine Electrics Harness with Labels
Cycle Works Inner Timing Cover Removal Tool
What’s Under the Inner Timing Cover
Crankshaft Nose Bearing and Sprocket in Cycle Works Removal Tool
Installing Bronze Color Back Plate With Screw Driver Blade
Verifying Crankshaft and Camshaft Sprocket Orientation (White Marks) After Installiing Timing Chain
