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Thread: Very strange spark issue!

  1. #31
    Registered User beano08's Avatar
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    follow up question... is there anyway to mess a rotor test up? I've got my meter set to both 200 and 2k Ohms both with no change. That would seem to indicate an open rotor correct?

  2. #32
    Quote Originally Posted by beano08 View Post
    I'm blown away by you folks taking time to help a fella out. Ok i've got the bike apart right now and I think I may have found the issue! My rotor is showing open. There's no ohms coming up on my multimeter. But going back to an earlier question, how is it that I'm still getting a gen light? Is there any conceivable way that these bikes can have a bad rotor and a gen light on?
    The only time I have seen that was when the rotor was temperature sensitive and would show OK cold and open hot. The other way it can happen - discovered after 3 days in a sheep barn at the National rally in Lima, Ohio, is if the wires at the alternator brush connections are mis-connected. The brown must connect to the ground brush and the blue or black must connect to the hot brush. Check this!

    If reversed the circuit through the bulb is connected directly to ground but not through the rotor.

    Thanks Oak (RIP) for helping me fix this on Leland Prothe's bike.
    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/

  3. #33
    Registered User beano08's Avatar
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    Well now I'm a bit dejected. I'm almost certain my meter is working correctly, and I'm very certain my charging light is on. So what gives? My brushes haven't been off since I've owned the bike and they're showing nearly 9mm exposed from the housing

  4. #34
    Registered User m_stock10506's Avatar
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    Since Oak's Top End Manual was mentioned earlier in this thread, I'll update that I received my copy of the manual in today's mail. So, Carol Okleshen (or someone in the family) is still filling those orders.
    Michael Stock, Trinity, NC
    R1100RT, R100, R60/6

  5. #35
    Curmudgeon nrpetersen's Avatar
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    Angry

    The very worst rotor failure I've had to diagnose is one in which the rotor opened only when at speed, but regained continuity when slowed down.
    Retired w 2005 K1200LT, 2000 R1100RT, & 1975 R90/6

  6. #36
    Curmudgeon nrpetersen's Avatar
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    Quote Originally Posted by beano08 View Post
    follow up question... is there anyway to mess a rotor test up? I've got my meter set to both 200 and 2k Ohms both with no change. That would seem to indicate an open rotor correct?
    Normal rotor DC resistance will be on the order of maybe 10 to 30 ohms. Your 200 ohm scale should show that. Assuming DVM is displaying full scale (200+) ohms means the rotor is open.
    Retired w 2005 K1200LT, 2000 R1100RT, & 1975 R90/6

  7. #37
    Registered User beano08's Avatar
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    Hey stuff happens. I've checked every piece of the of the charging system based on tips from from the good folks on here and the rest of the knowledge on the web. Everything seems fine besides my rotor that appears to be open. Just looking at it, indicates that it may even be original 64K. Plenty of rust on the housing and some cracking of the sealant they used on the copper. I guess I'll be making a call to Rick on Monday. I'm still bothered by the fact that I did have a charging light at all time, but snowbum does list an open rotor as a likely cause of a full time charging light.

  8. #38
    Day Dreaming ... happy wanderer's Avatar
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    Quote Originally Posted by beano08 View Post
    Hey stuff happens. I've checked every piece of the of the charging system based on tips from from the good folks on here and the rest of the knowledge on the web. Everything seems fine besides my rotor that appears to be open. Just looking at it, indicates that it may even be original 64K. Plenty of rust on the housing and some cracking of the sealant they used on the copper. I guess I'll be making a call to Rick on Monday. I'm still bothered by the fact that I did have a charging light at all time, but snowbum does list an open rotor as a likely cause of a full time charging light.
    The circuit that turns the gen light on is not typical at all. It is very cleverly designed that will light the bulb if the voltage is too low on _either_ side of the bulb. The first time I tried to wrap my electronics tech brain around this I said that's impossible. Then I looked at the circuit for quite some time and read Snowbum's section on it and the way they did it is actually brilliant. So yes, it is possible that the bulb goes on with an open rotor.

    You see, the trick is that the bulb does not care if current flows one way or the other so in order for the light to go OUT the voltage on both terminals of the bulb must be EQUAL. That's a huge clue into understanding how it works. Now just go stare at the schematic for an hour like I had to until the bulb in my brain turned on.
    MJM - BeeCeeBeemers Motorcycle Club Vancouver B.C.
    '81 R80G/S, '82 R100RS, '00 R1100RT

  9. #39
    If the rotor windings are shorted to ground it is possible to have the current illuminate the bulb and at the same time lack continuity from slip ring to slip ring. Try testing continuity from the hot brush to ground with just the ground brush isolated from the rotor with a business card or similar.
    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/

  10. #40
    Registered User toooldtocare's Avatar
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    As others have said, vibration can cause all sorts of problems with electrical circuits, including those you are having. Often the only way to fully troubleshoot the issue is to replace the suspect part and see what happens.

    Wayne

  11. #41
    Heartbeat of my R100GS Guenther's Avatar
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    A good rotor has about 3 Ohms. Depending on the voltmeter set for resistance an open rotor shows either a very high resistance or displays some dashes. If it shows close to zero (< 1 Ohm) you may have a shorted rotor. In which case the GEN light would be on all the time but no charge.

    When in doubt measure the rotor resistance again!

    What happens when you disconnect the wires to the brushes. Does the GEN light still stay on? If not it points to a short in the rotor.

    /Guenther
    Last edited by Guenther; 10-23-2017 at 11:57 PM.

  12. #42
    Registered User beano08's Avatar
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    I did not measure voltage to the brushes, I wish I would have done that before everything came apart. But in speaking with Rick, and with what some have said on here, although it's some what rare to have a full time gen light it seems likely the rotor has failed. The new one is in the mail. I'll keep you all updated! While I have everything apart, are there any other less obvious connections I can check in order to get the most out of my charging system?

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