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redavide
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The red charging light on my R69 was not going out even at high RPMs and I noticed some sparks coming off the generator brushes after removing the front engine cover. After I held a fine piece of sandpaper on the armature while the engine was running, the sparks disappeared, the light went out and I tested the charging system with a voltmeter -- everything was back in order. Then I took the bike out for a daytrip of about 200 miles and at the very end of the trip the red light was back on. I sanded the armature again and the problem went away again.

Anyway, I suspect the brushes might be due for a replacement. How can I tell if they're still good? How do you go about replacing them?

Thanks.

schrader7032
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VBMWMO #7032
San Antonio, TX
Joined: 10/27/2006
Posts: 6885
R69 Generator Brushes

Have you looked through this manual?

http://www.snafu.org/restore/uandm_bmw_v1.pdf

It doesn't say much about the brushes specifically but it does fully describe the system and how to trouble shoot it.

I'm not sure I understand why the sparks are coming from the brushes against the rotor and that sanding the rotor clears it up and makes the generator work again. I would have thought that the contact area on the rotor would be very smooth. If it's getting pitted or picking up bits and pieces from the brushes, maybe the rotor is at fault.

Do the brush springs have adequate tension to hold the brushes firmly against the rotor? I don't know what the proper length is supposed to be. On my /7, the time to replace the brush is when it is about 12-13mm long.

As for replacement, it's pretty simple. Carefully pull the spring out of the way. The wire to the brush is on a screw down terminal. Unscrew and replace and carefully reengage the spring. While the brush is out, clean the brush housing.

Kurt in S.A.

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Kurt in S.A.
'78 R100/7 '69 R69S '52 R25/2

redavide
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R69 Generator Brushes

Kurt, Thanks for the info., the link to the article on electronics was very good.

When brushes reach their minimum recommended length, what happens? What are the first symptoms?

schrader7032
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VBMWMO #7032
San Antonio, TX
Joined: 10/27/2006
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R69 Generator Brushes

"redavide" wrote:

When brushes reach their minimum recommended length, what happens? What are the first symptoms?

I'm thinking about how things work on the /5-on alternators which probably apply to the /2 as well. The pressure of the brush on the rotor lessens. When that happens, the brush could bounce a bit and contact would be intermittently lost. Without contact, there's no continuity through the rotor to ground and charging would decline and you would see the red light come on.

Kurt in S.A.

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Kurt in S.A.
'78 R100/7 '69 R69S '52 R25/2

kwalther
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maryland
Joined: 09/08/2008
Posts: 17
R69 Generator Brushes

I had the same trouble with my 67/2 at its worst the brushes would stop working after about 100 miles.Found out that the armature they ride on was worn down to much. When i got a replacement the trouble went away.
That said replacement can be should we say rather expensive. There is a place in calf. called erton electronics that can rebuild the armature on the end of the generator. They can also rewind it if needed.
I got 2 of them done one cost 130$ to rewind and the other was 150$ cause it needed rewind and the armature redone.
They did fine work and I was quite pleased.
If you go to there web site they have a list of things they do and it listed antique bmw generators so that is why I called them.

hope it helps
kurt

redavide
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R69 Generator Brushes

Kurt, It's got a "new" rebuilt, rewound armature, so at least that shouldn't be the problem. But you never know with these things, sometimes the rebuilt or new ones aren't perfect. I bought new brushes the other day, so I'll try those first and see what happens.

schrader7032
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VBMWMO #7032
San Antonio, TX
Joined: 10/27/2006
Posts: 6885
R69 Generator Brushes

"kwalther" wrote:

There is a place in calf. called erton electronics that can rebuild the armature on the end of the generator. kurt

Kurt -

Do you have any more specifics on this company? I tried to find them on the web but came up empty. Thanks...

Kurt in S.A.

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Kurt in S.A.
'78 R100/7 '69 R69S '52 R25/2

kwalther
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maryland
Joined: 09/08/2008
Posts: 17
R69 Generator Brushes

Sorry got name wrong
Eurton electric co. inc. santa fe springs. ca.
800 423 4789
www.eurtonelectric.com

cost me 135 to get one rewound and 175 for a rewind and fix the comutator end.All the places around so. maryland wanted 250 for a used one and over 500 for a new one.I think i did ok as the bike is just a big boat anchor without that part.
The guy I delt with was very nice and turn around wasn't to long.

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