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  1. #1

    Charging Issue?

    Finally some nice weather so I decide to ride the 1983 R100RS down to St Louis to see my son. About an hour from home, the volt meter drops to just a hair under 12 and the red generator light starts to glow faintly. Normally the volt meter points to between 13 and 14 when cruising at highway speeds and, of cours, no red light. I need gas so I stop, fill the tank and have a short pit stop. When I restart the bike, volt meter goes back to between 13 and 14 and the red light goes out. Stays this way for the remainder of the trip (two more hours). The bike has 63,000 miles on it and had a new battery in April 2016. When not in use the bike is always on a Battery Tender. Pretty sure the bike is sending me a message here and since I want to take the bike on a trip this summer (1000 miles round trip) would appreciate hearing any ideas about what is going on.
    "The universe is made of stories. Not of atoms."
    MOA 7935

  2. #2
    Registered User STEVENRANKIN's Avatar
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    Possible solution

    It is possible that one of the brushes on the alternator hung up or was not making contact for a bit. I had this happen after the bike sat for the winter.
    When was the last time the brushes were checked? They could be worn out or the springs could have lost their spring.

    Of course, there could be a whole lot of things going on from a dirty contact/connection to a major failure. Problems that show up and then go away are such a pain to track and fix.

    Good luck. St.

  3. #3
    Day Dreaming ... happy wanderer's Avatar
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    Ohhhh this sound soooo familiar! The last time I had this behaviour I diagnosed the problem to be the diode board. Replacing it fixed my issue but I got curious and examined the bad diode board with a magnifying glass. What I found was that one solder joint on one of the big diodes had come loose and the diode lead was floating in the hole. It was very hard to notice at a glance. I just put a lot of solder flux on the joint after cleaning it up with a brass brush on a dremel tool and re soldered it with some good acid core solder.

    Put it back in and the bike ran fine for a few more years. I have carried the new one as a spare on whichever airhead I am traveling on ever since. And we all know if you carry a spare that part NEVER breaks down on the road!

    What happens is heat makes the metal solder joint expand and it loses contact. Then it cools down again and sort of makes contact again which is very frustrating to trouble shoot! I think the newer diode boards with that covering on the back are not as susceptible to this as the old ones were.
    MJM - BeeCeeBeemers Motorcycle Club Vancouver B.C.
    '81 R80G/S, '82 R100RS, '00 R1100RT

  4. #4
    Registered User m_stock10506's Avatar
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    217Don - I hope you realize that without symptoms now, it could be anything in the charging system. Both of the above possibilities are each good chances. At 63K miles, worn brushes are a good and cheap possible. Take a look at the site for Motorrad Elektrik. They sell replacement brushes with a ring terminal on the end. It makes it SO EASY to replace the brush. No soldering, just remove the screw and slip the ring on and tighten it back up.

    http://www.motoelekt.com/charging.htm
    Michael Stock, Trinity, NC
    R1100RT, R100, R60/6

  5. #5
    If all this bike is used for is very local riding it would be OK to wait till the defect becomes more prevalent and easier to diagnose. However if the bike is ridden beyond battery depletion range - say 100 miles - from home then I would take a more preventative approach. By that I mean a close physical examination of the system. Check the rotor for crud on the slip rings. Carefully examine the diode board, even with a magnifying glass looking for solder defects and any sign of blackening or heat. Check all of the connections for grime, looseness, or corrosion. Check the rotor for proper continuity cold and after being warmed with a hair dryer.

    If that provides no apparent remedy than I would at a minimum carry a spare diode board and spare voltage regulator.
    Paul Glaves - "Big Bend", Texas U.S.A
    "The greatest challenge to any thinker is stating the problem in a way that will allow a solution." - Bertrand Russell
    http://web.bigbend.net/~glaves/

  6. #6
    Thanks for the suggestions. Since I made it to St Louis, I had it checked out by the BMW dealer there. They said brushes and ground were good and could not find anything wrong with the charging system. Hot or cold it seemed to crank out 14 volts. I really would like to take it on a trip this summer up the Great River River Road.
    "The universe is made of stories. Not of atoms."
    MOA 7935

  7. #7
    B Reams brook.reams's Avatar
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    Hi 217Don,

    There is a potential problem with how BMW mounted the diode boards on the 1983 (and other year) bikes. They used rubber vibration isolation mounts that crack and fail. When I opened up my front engine cover, the diode board was hanging by two of the four rubber mounts on my 1983 RS.

    There are also issues with these mounts getting a good ground path. Should the ground path be intermittent, you will experience intermittent charging.

    Rubber Mounts-One Broken
    Rubber Mounts-One Broken

    You can learn more about this, see how to test your diodes, and see how you can replace the rubber mounts with solid metal mounts that insure a reliable ground in this document on my site.

    12 BMW 1983 R100RS Check Diode Board, Replace Rubber Mounts=

    I hope this is helpful.

    Best.
    Brook Reams.
    Brook Reams - Arvada, CO
    Endeavor to Persevere
    Various Two-wheeled Vices, All BMW || Website: Airhead Rebuild Projects
    2004 R1150-RS||2002 F650-GS||1983 R100RS||1977 R100RS||1973 R75/5

  8. #8
    Registered User PAS's Avatar
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    That regulator doesnt look like the mechanical one that came on my 81 R100RT. Mine was taller with a removable metal cover so you could adjust the contacts. The newer electronic ones are low profile like the one you posted.

  9. #9
    Quote Originally Posted by brook.reams View Post
    Hi 217Don,

    There is a potential problem with how BMW mounted the diode boards on the 1983 (and other year) bikes. They used rubber vibration isolation mounts that crack and fail. When I opened up my front engine cover, the diode board was hanging by two of the four rubber mounts on my 1983 RS.

    There are also issues with these mounts getting a good ground path. Should the ground path be intermittent, you will experience intermittent charging.

    Rubber Mounts-One Broken
    Rubber Mounts-One Broken

    You can learn more about this, see how to test your diodes, and see how you can replace the rubber mounts with solid metal mounts that insure a reliable ground in this document on my site.

    12 BMW 1983 R100RS Check Diode Board, Replace Rubber Mounts=

    I hope this is helpful.

    Best.
    Brook Reams.
    I noticed that you posted photos of an RS rebuild. Looks like you used vinegar and water to clean contacts and baking soda and water to stop the reaction. What proportion of vinegar to water did you find most effective? Lilewise for the baking soda and water mixture. Thanks.
    "The universe is made of stories. Not of atoms."
    MOA 7935

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