Alternator, Rotor, Stator, Brushes, etc.

Rotors and Stators:

This has been a confusing subject to many. Anton Largiader’s website article with text & photos will explain explain some things; or, some differently. I have minor disagreements with his article, BUT….it does have some useful information & has some photos you should look at. I have the most detailed and pertinent information here in my own article. Read Anton’s article here:

The original /5 BMW Airhead motorcycles had a 180 watt alternator with the end that fits into the motor timing chest cavity being 105 mm in diameter. SOME 1974-1975 /6 bikes, & possibly a few barely into 1976, were made with the 105 mm cavity. These /6 bikes with 105 mm stators had 280 watt alternators, so it is possible to upgrade a /5 from the 180 watt alternator to a 105 mm 280 watt alternator with the appropriate parts changes and the parts WILL FIT. These changes are stator & diode board, at a minimum. If your /5 rotor measures ~7 ohms, which was the original value, then I recommend it be changed to a next version rotor of ~3.4 to 4 ohms; the electronics VR is optional, but recommended. ALL /6 and later stators had a center tap on the stator windings, & some small diodes were added to the diode board. If you do not use the /6 or later diode board, the output will be less. I suggest NOT using the last version of the Airhead rotors, which were ~2.8 ohms. For all other /6 and all later Airhead motorcycles, the cavity and stator were 107mm.

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