Category Archives: MC Build Projects

Chronicles of my Motorcycle Build Projects

Availability of Airhead Electrical System Documentation

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I have been developing a growing library of airhead electrical system documents.  So far I’ve written documents that cover the /5 and /6 1975-76 electrical systems.

For each, I document the wiring system, circuit by circuit, with explanations of what goes where and with notes about well know problems. Another document describes how the electrical components work. I also wrote an Electrical System Basics document to help those who, like I was, are mystified about electricity and how it is applied to our airhead motorcycles.

I’ve been working on these documents off and on for the past two years and figured they might be helpful. You can find them using this link and they are listed on the right hand set of links on most pages.

I hope to add additional documents covering the 1977 RS and possibly the 1983 RS as I have both of those, have completely rebuilt the ’77RS and plan to do the same for ’83 RS soon.

I see more and more questions about electrical system problems, and I expect this to increase as these bikes get older. Many folks struggle with electrical wiring diagrams and don’t have a good understanding of how the electrical components work. So they are at a loss about how to proceed with fault isolation and problem solving. I found that writing this material helped me learn much more about the electrical system and improved by diagnostic capabilities. That’s one reason I wrote these documents; writing things down really helps me learn.

I’ve digested a lot of material others published, among them are Bob Fleischer, Duane Auscherman, Anton Largiader, Tom Cutter and many of the questions and answers that have appeared in the various airhead forums including the micapeak airhead news group and the BMW MOA airhead forum. To all of you, thanks for sharing your knowledge.

I hope this material is helpful.  Have a great New Year.

Repair Stripped Cylinder Head Stud Threads in the Engine Block

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The first sign of the problem was this bike would not idle well. I thought the carburetors got dirty and all I needed was to clean them. But, before I started on that task, I decided to check the valves and I found the left intake valve lash was 0.012 inches instead of 0.004-0.006 inches. Hmmm …. how did that tappet get so loose?

Before I reset the valve clearance, as I always do, I torqued the cylinder stud and head bolt nuts to 25 Ft/Lbs. But, one stud just spun.  Bummer. That means the threads in the engine block are stripped.

It turns out a friend of mine, Dick, had the same problem on his 1972 R75/5 a couple of weeks earlier. I contacted him and learned he made arrangements to rent a jig to repair his stripped threads from Northwoods Airheads. So, we jointly repaired our stripped threads in “Brook’s Airhead Garage” when the jig arrived.

This write-up is based on the work we did on both bikes.

Here is a link to a video of how to use the Northwoods jig to drill out the damaged threads, tap new threads for a 20 mm long M10x1.5 Heli-Coil insert, and install the insert.

 

Airhead Electrical Systems Documents

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I put together a series of pages about BMW airhead motorcycle electrical systems. It strikes me that electricity in general, and motorcycle electrics in particular, are dark mysteries to many, so I thought I’d shine some light [puns intended 🙂 ].

Lack of understanding hinders confidence when diagnosing and working on electrical projects. As these bikes age, the electrical system is prone to problems as corrosion and neglect makes them behave badly. More owners are having more electrical problems but seem less able to get to the root cause of the problem.

I think one tool that many avoid using is the wiring diagram. The spaghetti of lines, symbols and notations makes the eyes glaze over. “Oh goodness, where do I start?” is the common response to the advice, “Look at the wiring diagram.”

5 Series Wiring Diagram (1970-1973) (Source: Haynes Manual) –> CLICK TO ENLARGE

I’m not an electrical engineer, but I have taken time to learn the basics, have collected comments and input from well respected airhead mechanics and dug into how BMW applied electrical theory when they designed the /5 electrical system. I’ve learned a lot from various reference sources that are scattered about the internet, so my articles include a bibliography of various useful resources. That way both you and I have a nice set of reference materials to consult when problems come up.

I have published three articles (so far), Basics and two about the /5 series: 5 Series Electrical Circuits and, 5 Series Electrical Components. I chose the /5 series to start with because I believe it’s the most popular airhead series for restoration.

I hope to write an Electrical Circuits and Electrical Components document for the /6 and /7 series up to 1984.

Here is the table of contents from the first three documents.

Airhead Electrical Systems-Basics

Airhead Electrical Systems-5 Series Circuits

Airhead Electrical Systems-5 Series Components

 

 

 

1977 BMW R100RS Transmission Work

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It has taken some time, but I finally finished writing up the work I did on the transmission, and you can find it here.

I included several short videos that show how the transmission gears and the shift cam assembly work, and several that cover other details of the work.

Here is a play list of all the YouTube transmission videos I made.

This is the most critical, precise piece of work I’ve taken on. Before doing this project, I did a lot of research. I had access to special tools, a shop press and advice from two local airhead mechanics. Without those resources, and spending a couple months trying to learn what I needed to know about this work, I wouldn’t have attempted to do it.

Despite all that, I managed to overlook a new, but wrong size, $2.95 circlip that holds the cam roller on it’s pin. It separated company from the pin about 2000 miles after I finished rebuilding the bike. I was in Indiana at the time on my way to the 40th RS rally in Pennsylvania. Mr. Cutter, who was attending the rally, stepped in and devoted a Sunday to save my bacon. Watching him do the work in a day I had labored over for weeks reinforced the value you get from someone who has spent 45 years making mistakes and learning from them so you don’t have to 🙂

So, in retrospect, I should say I relied on three airhead mechanics to do this work 😉

1977 BMW R100RS 4400 Mile Status Report

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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