NGC - airhead charging system

[Wayne Orwig]

If the dash light is on, and staying on, the brushes and rotor are likely to be fine.
Of course, things happen, but I would start with suspecting the diode board.

[ohiorider]

If the dash light is on, and staying on, the brushes and rotor are likely to be fine.
Of course, things happen, but I would start with suspecting the diode board.

Hi, Wayne,

Good to hear from you.  The diode board is the original, 29+ years old. 
I just finished running a couple of Rick Jones (Motoraad Elektrik) tests.
1. DF disconnected from brush holder.  Red BATT lite came on when grounded DF wire to engine.  What it should do, if circuit good.
2. Reconnected DF terminal, ignition on, bridged both copper rings.  Red BATT lite was already on and stayed on when I bridged.
3. Ignition off/brushes lifted and insulated from rotor with cardboard.  Ohmmeter showed 2.8 ohm when probed = Rotor not open.

I've got an older diode board I could swap in and see if that makes any difference.  And test the one now on the bike.  Probably will also buy set of brushes and brush holder.  Mine look a little short.

Bob

[wirespokes]

On the other hand, the rotor winding could have failed shorting to ground, in which case the light would always stay on.

The easy quick way to tell if the brushes are worn too short is if the coiled snail spring is resting on the edge of the brush holder and unable to press on the brush. When that happens out on the road it's possible to put the brush in sideways or put some shims (cardboard?) between the spring and brush. That will be enough to probably get you several thousand miles back home.

When brushes start getting too short they'll make contact some of the time but others not. The slip rings aren't perfectly true so cause a little bounce in the brushes. I think they'll make better contact at lower RPMs and the light will come on at higher revs.

Another thing that happens and could be your case here with the high miles: the brush holder wears and the brushes can jam. With that 'bounce' they can be forced up away from the slip ring and not make contact.

I've gotten a lot of bikes that sat for years and put them back into service. An R65 stranded me eight miles from home one day with a dead battery. Everything checked out fine. I've been told the slip rings benefit from the dark color and whatever it is the brushes do to cause that, but I cleaned it off. Everything was fine after that. Evidently the old brushes had coated the slip rings with some sort of non conductive layer.

[ohiorider]

On the other hand, the rotor winding could have failed shorting to ground, in which case the light would always stay on.

The easy quick way to tell if the brushes are worn too short is if the coiled snail spring is resting on the edge of the brush holder and unable to press on the brush. When that happens out on the road it's possible to put the brush in sideways or put some shims (cardboard?) between the spring and brush. That will be enough to probably get you several thousand miles back home.

When brushes start getting too short they'll make contact some of the time but others not. The slip rings aren't perfectly true so cause a little bounce in the brushes. I think they'll make better contact at lower RPMs and the light will come on at higher revs.

Another thing that happens and could be your case here with the high miles: the brush holder wears and the brushes can jam. With that 'bounce' they can be forced up away from the slip ring and not make contact.

I've gotten a lot of bikes that sat for years and put them back into service. An R65 stranded me eight miles from home one day with a dead battery. Everything checked out fine. I've been told the slip rings benefit from the dark color and whatever it is the brushes do to cause that, but I cleaned it off. Everything was fine after that. Evidently the old brushes had coated the slip rings with some sort of non conductive layer.

The front brush snail spring does look like it could be resting on the brush box.  You also mentioned the possibility that the brushes  can jam.  Well, this little item is on its way ...... new brushbox, brushes, springs.  So, if its a brush issue (and it could be) this should eliminate brushes from the equation.  May have posted earlier that I did check the resistance between the copper rotor rings by insulating the brushes from the rings and taking a reading.  It read exactly where Rick Jones said it should, if the rotor was good ....... 2.8 ohm.

Thanks for your suggestions.

Bob

https://www.euromotoelectrics.com/Bosch-Alternator-Brush-Kit-BMW-R-Airhead-p/boalt-brushholder.htm

I'm getting there slowly, but think I'm making progress.

[ohiorider]

OK, all of you who admonished me for not first checking the brushes ........ I stand corrected and embarrassed!  Once I pulled the front cover off the R100GS, I looked at the front brush (still in the holder) and it looked sort of ok, and I was about to move on to something else.  But in the process, I removed the stator cover (brush holder)  and found the rear brush was practically non existent!

So I thought I'd put the kit on the bike, consisting of brushes, new holder, and a zillion washers and assorted crap ...... AND no damned directions!  I'm bad at electricity, aside from using a toaster at breakfast. 

But my good buddy and neighbor took one of his old 8mm, 12 pt end wrenches, ground it thin, heated it, and put a bend in that would let me remove the little brush holder from the stator cover.  What a nasty, thankless task!

I finally got to the point where I decided to reuse the  brush holder and springs that were on the bike.  Unlike the worn brushes on the bike, the new ones didn't have to be soldered, but had fittings that would go over the two studs that held the brush holder.  By this time, I wasn't sure if anything was going to work, but I had noticed that the brush attached to the DF wire had an insulating bush, and the other brush (D-) did not, so I attached the two brushes to the studs, and put everything back together, not knowing what to expect when I flipped the ignition on.

Amazing!  The red BATT lamp came on brighter than I'd seen it for years.  And like it should, it went out when I started the engine, at slightly over 1000rpm, and stayed out as I increased rpm.

Checked the voltage at the battery at 3000rpm and 4000rpm, and I was seeing over 14vdc.  Again, I'm amazed!

Took her for a ride in the park, keep revs above 3000 when I could, got home and measured battery voltage.  12.98!

Long and short of this story ....... if I'd had instructions telling me specifically how to attach the brushes, I'd have been done yesterday.

Now I know.

Bob

[Moparnut72]

Hate to say it but toad ya so. I rode air heads for many years. Usually the case. Not trying to be mean.     
Check the easy things first. Might get lucky. Glad you are all good.   
kk

[wirespokes]

Not sure why that is, but the rear brush seems to wear faster than the front one. Just looking at the front one can fool you into thinking they're ok. I've seen that a number of times.

Well done getting it fixed! 

[Testarossa]

Ayup.

[Kiwi_Roy]

Not sure why that is, but the rear brush seems to wear faster than the front one. Just looking at the front one can fool you into thinking they're ok. I've seen that a number of times.

Well done getting it fixed! 

Different polarity, transfer of electrons from one brush to the other.






ok





i'm




BSing




But it sounds good



I should know the answer to that, I cut my teeth on brush type machines.

[Testarossa]

Dunno either but could be as simple as better cooling for the front brush. Hot brush runs softer.

[wirespokes]

Hadn't thought of the 'cooking' aspect but that's possible. I always thought it was something to do with the direction of electrical flow like Roy suggests, but who knows?

[Testarossa]

I meant cooling of course (fixed it).