Forum bmwbike.com

Recently my Charge Indicator Lamp did not want to turn off after start.
Having had the same trouble some time ago, and - after consulting the manual - I could
fix that problem by changing the carbon brushes.
So I checked them again and they seemed to be quite worn, but not very.
Down to about half of their original length, which I found much for only 5000km.
Anyway, it did not solve the issue, so I checked the regulator (swearing heavily
about the person, who designed it to be where it is and how it is attached).
I cleaned the contacts, but everything looked fine so far.
Still did not solve the problem. So I checked the generator as good as I could:
no voltage.
I rode for some days just on the battery with no light and re-charged from time to time.
Now it works again! But why?
I followed the thread about depolarization from Allan Atherton - could this be caused by
worn brushes? Could a generator have some sort of intermittent failure mode?
Presently I am riding without the lid and see heavy sparking around the brushes,
is this normal?

Rolf,

I had the same symptoms om my R50. It turned out to be the bad condition of the collector of the rotor. I reconditioned the segments of the collector by taking off the stator part of the generator, having idling the engine (I think this is possible with a R27) and then with a piece of fine sandpaper between my fingers rectifying the turning collector until all irregularities disappeared. Now during operation of the generator I have only small inoffensive sparks between brushes and collector.
Try this remedy first before digging any deeper.
Good Luck

Han Verhagen

Hi Han,

thanks for the hint. I used your principle, just letting the engine idle and pressing a 600 grade sandpaper slightly against the collector until both turned from coal-black to a nice copper colour.
Also I could not resist the temptation to spray a bit of WD-40 on it (maybe not good, but it made it even more smooth).
Now everything is fine again, but I still don't understand, how it could have repaired itself.

Cheers Rolf

Hi Rolf,
No, there should not be any sparking between the brushes and commutator. The brushes might look alright but don't take that for granted.
It is often the case that when a brush wears the light springs that holds it on to the commutator touches the side of the brush guide, relieving its pressure on the top of the brush and thereby causing arcing, a glowing ignition light that will eventually remain on.
The only answer is a new set of brushes. Ensure the brushes slide perfectly freely up and down thier guides - they may need to be lightly trimmed by carefully using a piece of fine emery cloth on a smooth, flat surface.
The advice on cleaning the commutator is valid only if the commutator is running undamaged, unburned and true. Ideally it might need to be skimmed by a competent auto-electrician.

Hi Gerry,

problem is solved now (my reply to Han) - still leaving me in the dark, why. Thanks a lot
for your suggestions. Yes, brushes were worn, maybe due to rough collector, maybe due to soft material. Now they run smoothly and most importantly , I get power from the generator again.
I am pondering, whether I should install the 12V system from mz_b. Looking for people with experience here - good or bad.

Cheers Rolf_B

I wouldn't get WD40 or anything like a solvent anywhere near the old insulated wiring that winds a generator.

Hi Rolf,
I have an MZ system on my R27. It works well in that it replaces all the points and provides a nice 12V charge but it is not a battery / coil system, so needs a fair kick to get it going, whereas the old system would start with a modest kick only.
One set of coils provides the spark, timed by the rotor positioning and advanced by electronics, and the others (separate) provide power to the battery. I think if I had my time over I would modify the existing battery coil to 12V as some on this forum have done, as the ability to use the new 12V LED lights and halogen headlights is certainly nice, but the need to really get it spinning fast to start it with the MZ systemn is a pain - as stated in my earlier post, I usually bump start it.. MZ say they may build a battery start system for the R27 as they have done for other makes..