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Thread: 79 R 100 RS charging issue

  1. #1
    Moose
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    79 R 100 RS charging issue

    I wonder if there is anyone out there who can offer some advice.
    I have a 79 R100RS that has a good battery that takes a charge, and rides for a day or two, but then battery dies.
    I have been reading forums here, and have tested the ohms on the rotor while insulating the brushes, and they are 2.5-3.5, but also keep in mind my meter is not digital.
    I have checked the bulb in the insturment cluster and it is not burned out.
    How can I test the brushes, and how hard are they to replace?
    If it is not the brushes then what else could it be?
    My thought is to now just replace the voltage regulator and brushes, but could it also still be the diode board?

  2. #2
    Liaison 20774's Avatar
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    Rather than shotgunning this, you should step through a process to figure out what's wrong. Some resources that you should be aware of:

    Rick at Motorrad Elektrik - has a great book for doing this troubleshootting; suggest you get it and carry it with you, especially on trips

    Snowbum's site - http://bmwmotorcycletech.info/trbleshootALT.htm

    OK some questions:

    - does the charge light come on when the key is turned on but the engine is off? Does it then go out after the engine is started and the revs come up to say 1500 and above? If yes, then that part of the system is working correctly.

    - what is the voltage across the battery terminals with the engine revving to 3K or higher? It should be 13.5v or higher. If it's over 14.5v, you have another problem, that of overcharging and possible damage to the battery and wiring.

    Beyond that, you need to consider the information above and/or get the book from Rick. Or possibly find a local Airhead who can help you walk through this.
    Kurt -- Forum Liaison ---> Resources and Links Thread <---
    '78 R100/7 & '69 R69S & '52 R25/2
    mine-ineye-deatheah-pielayah-jooa-kalayus. oolah-minane-hay-meeriah-kal-oyus-algay-a-thaykin', buddy!

  3. #3
    Moose
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    Thanks for the response

    The charge light does not come on at all, not even when ignition is on, and engine off.
    The voltage reads between 10.5 and 11 with the engine over 3k.
    Thanks for the heads up about the book, I'll look into that.

  4. #4
    Quote Originally Posted by Mike Steed View Post
    The charge light does not come on at all, not even when ignition is on, and engine off.
    That is a problem.

    The voltage reads between 10.5 and 11 with the engine over 3k.
    Hmm..

  5. #5
    Liaison 20774's Avatar
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    Quote Originally Posted by Mike Steed View Post
    The voltage reads between 10.5 and 11 with the engine over 3k.
    Looks like you're not charging, but then we knew that! The bulb issue bothers me...it really should be on with key on-engine off.

    Start with the easy stuff first...find out why the bulb is not lighting up...it's a critical part to the charging system. The bulb is a path for the battery voltage to get to the rotor for initial energizing. If that doesn't happen, the spinning rotor won't generate any current.

    From your first post, the rotor might be OK if I understand what you did. It could also be going open when operating, resulting in no charge. Bypassing the regulator would tell you if it's working or not.

    Yup, get the book and do some troubleshooting.
    Kurt -- Forum Liaison ---> Resources and Links Thread <---
    '78 R100/7 & '69 R69S & '52 R25/2
    mine-ineye-deatheah-pielayah-jooa-kalayus. oolah-minane-hay-meeriah-kal-oyus-algay-a-thaykin', buddy!

  6. #6
    Registered User skiteach's Avatar
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    Brush not contacting rotor is among the things to check, for a no lite/no charge.
    '73 R75/5
    Never had a bad day skiing!

  7. #7
    --Tony AnnapolisAirhead's Avatar
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    Quote Originally Posted by skiteach View Post
    Brush not contacting rotor is among the things to check, for a no lite/no charge.
    +1 on that. I think he said the rotor showed 2.5-3.5 Ohms resistance between the sliprings, so I'd say its ok (e.g. not a shorted rotor).

    The brushes may be worn and/or the springs that hold them in contact with the slip rings.

    I wonder if the diode board is good and connected properly to clean connectors.
    1971 BMW R75/5 | 1975 Moto Guzzi 850T Cafe | 1983 BMW R100RS | 1988 BMW R100GS
    1988 BMW K75 | 1998 BWM R1100RT | 2000 Moto Guzzi Quota 1100ES |2002 Moto Guzzi V11 LeMans

  8. #8
    Moose
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    brushes

    Thank yall so much for the replies to this post. I am fairly new to the airheads(bought one about 18 months ago), but I love them and want to learn more about them.
    I think I am going to see if the brushes are making adequate contact by pushing them down some. I read another forum post where someone with a /6 had a charging issue, and the brushes were not making good contact, but worked fine once he pushed them down. If it charges after that, then I will know the brushes are the issue and I can change them.
    I have heard it is a tough job to change the brushes, is this true?

  9. #9
    Liaison 20774's Avatar
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    Quote Originally Posted by Mike Steed View Post
    I have heard it is a tough job to change the brushes, is this true?
    You need the right tools and have a pretty good soldering iron. I tried once on my /7 and gave up. Be careful taking off the stator...three bolts hold it on and it maybe be wedged on. Use something like a piece of wood to gently rock the cover off.

    Getting at the outside brush is quite easy. The inside brush holder is what got me. I couldn't get enough bight on the 8mm (IIRC) nut that was holding it in place. So, I just buttoned things back up and will worry about it later. No real charging problems at the moment.

    The thing that's important on putting on the new brushes is getting the solder point hot enough since there's a fairly big area. I think there are two options for connecting the new brushes. One is at the far end of the brush where the wire ends. The other is to cut the old wire and splice in the new wire. If you do that, it's important to not get the joint of wires and solder too stiff otherwise it will restrict movement of the brush.

    The other thing is to be sure that the snail springs that are pushing on top of the brushes are not bottoming out on the holder...that could be your problem. When installing the new brushes, be sure the springs are wound correctly and providing ample pressure.
    Kurt -- Forum Liaison ---> Resources and Links Thread <---
    '78 R100/7 & '69 R69S & '52 R25/2
    mine-ineye-deatheah-pielayah-jooa-kalayus. oolah-minane-hay-meeriah-kal-oyus-algay-a-thaykin', buddy!

  10. #10
    Sir Darby Darryl Cainey's Avatar
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    Brushes

    Quote Originally Posted by Mike Steed View Post
    Thank yall so much for the replies to this post. I am fairly new to the airheads(bought one about 18 months ago), but I love them and want to learn more about them.
    I think I am going to see if the brushes are making adequate contact by pushing them down some. I read another forum post where someone with a /6 had a charging issue, and the brushes were not making good contact, but worked fine once he pushed them down. If it charges after that, then I will know the brushes are the issue and I can change them.
    I have heard it is a tough job to change the brushes, is this true?
    Hi Mike;
    If you need a set of brushes get them from Motorrad Eleckrik as they have the ends soldered on already.

    Do yourself a favour and geta copy of his book on Airhead Classic Boxer Charging
    it is the bible on electrical issues.

    http://www.motoelekt.com/

    Rick Jones has a wealth of knowledge and is glad to help!
    Ambassador Emeritus BMW MOA Ontario Canada
    Niagara Riders
    Knights of the Roundel #333
    1977 R100RS, (Retired) 1993 R100GS

  11. #11
    Moose
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    I found a local airhead that might help

    Thanks for the info, I have actually found a local retired guy who does some work still, and I am going to try and get an apt. with him today, but if he is not willing then I will have to do it myself.
    I'll keep yall posted.
    Thanks again.

  12. #12
    --Tony AnnapolisAirhead's Avatar
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    Quote Originally Posted by Darryl View Post
    http://www.motoelekt.com/

    Rick Jones has a wealth of knowledge and is glad to help!
    +1 on contacting Rick Jones.

    Even a veteran tech can make a mess out of soldering these things because the brush wires are braided so they are flexible. They tend to wick up the solder and become stiff. So while the problem may have seem to have been fixed, the stiff wire will break--and usually at the most inconvenient time.

    I think Rick sells a better version of these where the soldered joint is simply replaced with a spade connector, so no worries.

    You may want to measure the length of your brushes, or just buy new ones and new springs. They are not expensive and this way you'll know they are in good shape. I'd get them from Rick Jones.
    1971 BMW R75/5 | 1975 Moto Guzzi 850T Cafe | 1983 BMW R100RS | 1988 BMW R100GS
    1988 BMW K75 | 1998 BWM R1100RT | 2000 Moto Guzzi Quota 1100ES |2002 Moto Guzzi V11 LeMans

  13. #13
    Moose
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    Thanks again

    Thanks to all the posts for assisting me, but I have found a very reasonable shop that specializes in airheads to take it to and have the troubleshooting done.
    I do apprecite the experience here on the forum, and look forward to my next problem(as odd as that sounds), to be able to discuss things here.

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