I wanted a project bike so I obtained my first airhead. 1977 R75/R. That's what all the documentation says and all the serial numbers agree. The front cover looks like it might have a 1975 or 76 ignition sensor, it has the centrifugal governor. Doesn't show that on the 1977 fiche I have been looking at. The cover has 3 holes instead of 2 also as stated on the fiche. Did BMW mix/match? Attached is a picture. Anyway, how do you remove it?
The first photo shows the ignition cam with the centrifugal advance mechanism, usually called the "Auto Advance Unit". This is stock equipment for your year model. The center hole of the 3, the one with the D-shape, is supposed to have a stud. On that stud should be a nut and washer to retain the AAU onto the front of the crankshaft.
Your stud has snapped off. This is not unheard of. You'll need to remove the AAU by pulling it straight off. If the stud has left some exposed shaft, then you can latch on and turn it out. Usually though, the stud breaks off flush with the front of the crankshaft and a "stud extractor" has to be employed. This is professional level work. A small hole has to be drilled down the center of the remaining stud into which a small extractor is fitted. Not quick. Not easy. Not fun.
Ordering the replacement stud first can help you see what you are missing.
Owning an old Airhead is easy.
Keeping an old Airhead running great is the true test.
The 3 bolt front cover is standard stuff. When removing / installing that cover, one should always disconnect the battery (ground cable) to protect against accidental shorting to the diode board.
The centrifugal advance mechanism and point cam should pull straight off the front of the camshaft. Maybe need to soak it a bit with penetrating lube. You will have to inspect the condition of the nose of the camshaft. It appears that the threaded tip has broken off. There should be a full diameter smooth portion that the point cam fits over, then a short “D” shaped portion that engages the centrifugal advance, then finally a threaded tip for the 10mm nut and washer to retain the advance unit on the camshaft nose. Typically, if something breaks, it is the threaded tip that snaps off (folks tend to overtighten here). I don’t believe that the threaded portion is a replaceable stud. I think it is part of the camshaft.
If the threaded tip is gone -
1. If you doing a complete tear down and rebuild, you could replace the camshaft and start over.
2. I’ve heard of folks successfully drilling and tapping the nose of the camshaft, and using a small bolt and washer to retain the advance unit.
3. You can forget the whole advance unit and points (leave all that off) and install an electronic ignition system that triggers from the front of the crankshaft (alternator), rather than the camshaft. The Enduralast/Sachse system sold by Euro Motoelectrics is a popular option.
Your stud has snapped off. This is not unheard of. You'll need to remove the AAU by pulling it straight off. If the stud has left some exposed shaft, then you can latch on and turn it out. Usually though, the stud breaks off flush with the front of the crankshaft and a "stud extractor" has to be employed. This is professional level work. A small hole has to be drilled down the center of the remaining stud into which a small extractor is fitted. Not quick. Not easy. Not fun.
I think it snapped off some time ago and they added a stub shaft. I can now see some red loctite and the head of a screw where the nut is supposed to be on the AAU.
You can forget the whole advance unit and points (leave all that off) and install an electronic ignition system that triggers from the front of the crankshaft (alternator), rather than the camshaft. The Enduralast/Sachse system sold by Euro Motoelectrics is a popular option.
I think that's what I am going to do!
Thanks for all the replies!
This is the optical trigger unit (little green card + trigger wheel) on the front of the alternator (Enduralast system from EME).
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