Hello everyone. I wanted to come by and introduce myself to this part of the Airhead community. My name is Joe, and I started riding street bikes in 1974 and of the 20+ bikes I’ve owned, this is my first BMW. I’ve recently joined a few airhead online clubs because I know I will certainly need the expertise exhibited on the various Airhead forums, and as I learn the quirks and particulars of my bike, maybe I can pass on some help as you yourselves are doing here on the forum. I’ve actually wanted an airhead for about 25 years but my 20 year-old mind wouldn’t go for it, as all it wanted to do was strafe apexes on high powered corner-carving machines. Well, finally the mind conceded and the 66 year old body and mind are now talking. Long story short, I am currently attempting to get a 1977 R100RS roadworthy. It’s been sitting since 1995 and I am now slowly becoming acquainted with German engineering and the bike in general. I’m now finishing up the R&R of the steering head bearings and next on the agenda is the rebuilding of the front forks. When I first saw the bike, I didn’t give it a second glance because the fairing looked weird, being all bulbous and whatnot. After another bike I was looking at fell through, walked over and looked at the RS again. It was part of a collection and didn’t have a speck of rust on it. It is pretty original except for the seat which I will be replacing. It does have a few dings and wear marks as it wasn’t a restoration. Overall looked very sound. The owner started telling me about the 1977RS and how iconic of a bike it was, well, not being familiar with BMW’s, I took that as simply sales talk - until I did some research. Well, here I sit with Klaus in a boiling garage twisting wrenches and becoming friends. It’s good to be here and I hope to meet many of you as I begin this journey into the land of Muth. All the best.
Welcome Aboard !
You will quickly see that the quality of the parts and assemblies is VERY high. Older Jap and English bikes I had experience with needed total rebuilds to even crank. One thing you'll really like about the BMW is that you get to ride while you re-work. That is to say, you'll be able to ride the bike at the end of (typically) a 4 hour service. And then while you continue to ride and enjoy, you can continue to complete 1 or 2 small tasks per week. To that end... I would not rebuild the forks straight away, but rather simply change the fork oil as a starting place... unless the fork seal are too far gone.
Here is a good start-up list for the 1977 model:
Carbs
Carbs always need cleaning, of course, but Bing has issued new float needles and floats that are Ethanol-proof. Use this time to install all new jets and needles, while the float parts are being installed. Ethanol also attacks the "rubber" diaphragm and intake port hose. So those will be suspect.
Ignition
You may still have a "points" ignition. Cleaning the contacts will suffice, but you'll need to lubricate the Auto Advance Unit and replace the AAU return springs. Then, owing to the dramatic lowering of fuel standards, you'll want to strobe time your engine to the F mark at very high RPM. That is to say, at "full advance".
Plugs, plug wires and plug caps are generally replaced. It must be metal core plug wires and 5K Ohm caps. This is the cheapest insurance you can buy, because when they go bad due to age, the symptoms are very strange and very hard to diagnose.
Front Brake / Electrical
This will sound like a weird combination, but remove the fuel tank and you will find the front brake master cyl. Over time, especially time spent on the side stand, the m/c leaks caustic brake fluid onto the electrical system connections on the LH side of the frame at that location. As you can imagine, the quality of the electrical connections there suffer greatly. However, it is worse than you ever suspected in that the MAIN power from the battery going to the ignition switch (and thus lights and ignition) passes though the cubical Starter Relay and relay socket right in the middle of this "danger zone". After 40+ years the Starter Relay is typically shot and the relay socket is a totally awash in brake fluid. Even a hint of a poor electrical connection at this location grossly effects the ENTIRE electrical system. It may reveal itself as poor starter button response, but it will quickly come to effect other areas. This is a known and documented issue with 1977-1980 bikes. This schematic shows the Hows and Whys...
As you can see from the diagram, the main supply wire physically passes through the Starter Relay socket. This gives you not one, but TWO chances at complete electrical system failure. New "Dual 87" relays are $45 from BMW, or $6 from Amazon... your choice.
Other Stuff
You will undoubtedly have other questions, but this will get you started in a big way. Get set for a decade or more of great riding, and welcome to the fold !
Regards
Owning an old Airhead is easy.
Keeping an old Airhead running great is the true test.
@wobbly thank you so much for the welcome and reply! The master cylinder has been moved to the bars, the ignition system is electronic and it even has the later gear shift linkage installed. The right front fork was topping out with a bang, so there was more to deal with inside. Replaced very notched steering bearings yesterday and I’m making my way through a pretty extensive list of checks, adjusts refurbs or buys - ha ha. Appreciate the info very much, I’ll need it all. All the best. Joe
@wobbly thank you so much for the welcome and reply! The master cylinder has been moved to the bars....
You still need to wash off any residual brake fluid left behind. Hot soapy water is the trick. A LOW-pressure washer can be handy. You also still need to open up the mini-cube starter relay and check for age and prior brake fluid damage. And, you MUST treat the relay terminal prongs with anti-oxidation compound before replacing the relay.
the ignition system is electronic...
Then you need to check if it's an OEM unit. The stock ignition is a great unit, but it has one known flaw. The "white connector" coming from the "bean can" literally disintegrates over time. If the white connector isn't pristine, then it needs replacing because your ignition will suddenly quit one day. Motorrad Eliktrik sells a replacement connector, which is NOT shown on their web page. You have to call and ask. It's a good time to check the alternator brushes too.
Electronic or not, due to the poor state of American fuel, you MUST set the ignition at Full Advance with a strobe timing lamp. Let the Slow Speed timing fall where it may. Slow Speed timing doesn't matter one bit.
Replaced very notched steering bearings yesterday....
Most probably oxidized 40-year old grease, not rust or accident damage. (Bet your grease was the consistency of silicone caulk.) This is very common. In that case the bearings didn't need replacing at all, just cleaning and repacking.
This should set off an alarm bell in your head. If the grease in the head post has coagulated, then the grease in the wheel bearings and swing arm may be of a similar age and condition.
All the best.
Owning an old Airhead is easy.
Keeping an old Airhead running great is the true test.
@wobbly thanks for the reply and help! The I was hoping the steering roughness was indeed old grease, but both upper and lower bearings were more than covered with grease. The races were rough. The ignition is a Gerex unit, on which I have found little information, other than it was somewhat popular in the 70’s.
You're on your way !
Owning an old Airhead is easy.
Keeping an old Airhead running great is the true test.
Here's a full list of service items for you to check...
Owning an old Airhead is easy.
Keeping an old Airhead running great is the true test.
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