Vintage BMW Motorcycle Owners

Measuring resistance across the brushes through the slip rings and into the rotor quickly tells if there is an open circuit, rotors are known to break a wire internally, but in reality, there is not much data available as to what the ohm readings for a good system would be. Or at least I have never seen the values. LOL, I am lazy and don't have a rotor at hand nor the brushes and such to measure but what would the ohm reading be if there is an open rotor or brush not making contact. It has been so long since I measured ohms I forget, would the reading be infinity or zero? Sorry, I am just not accustomed to measuring ohms in that part of the system. Now if you give me an ignition coil with a ohm range, I can figure out if it is good or bad by the reading I get.

Maybe later today I will get the meter out and do an experiment to answer my dumb question. Nah, I will be riding.

Anyway, in this case, I really thing the culprit will be the voltage regulator. I am waiting to see. St.

It was the armature. I put the armature from my R60/7 on the R75/5 and it runs fine. Regulator works, relays work runs great. The R60 is a work in progress so I'll worry about it later. It was sunny and 75 degrees today - time to ride. Besides that it was bike night at my local pub so it was good to get out and put on a few miles - then top it off with a fermented malt beverage. Life is good.

Craig

Glad you narrowed the problem down. I thought the power output for the /5 and /7 series bikes were different and that was due to the different diameters of the rotors. I'm surprised that the /7 rotor would directly fit.

You won't be the first to have a rotor go bad. Glad you got it fixed. Thanks for letting us know. St.

You may also need to check the stator to see if the insulation is starting to break down. You will need to have it checked with a megohm meter.

Back in June I did a full replacement with the upgrade from EME so I could put the R60/7 back together.

Craig

ALL rotors, for Airhead motorcycles, should be interchangable.......albeit with varying OHM specs (these will determine WHEN the actual charging begins).
The STATOR, increased in size from 105mm to 107mm(?) in mid 1976. As a result, the later /6 and all /7 stators will NOT fit a /5 and early /6.
The /2 and earlier series are completely different.