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Thread: K1100RS Alternative Alternators

  1. #1

    K1100RS Alternative Alternators

    Hello all. I have about 800 miles on my new to me k1100rs (121xxx miles). Today whislt riding home the alternator area began making a very loud rattling noise. When I got home (5miles later) I found my bike would not start due to dead battery (brand new oddysey battery). After charging and starting the bike I preformed a voltage test and found I was getting 11v with the bike running(dead alternator). Does anyone know of affordable sources for replacement alternators? Beemer boneyard is unfortunately sold out. Also, has anyone heard of db electrical? They claim to make an alternator for this bike. I'll post a link below.

  2. #2
    Lee A. Dickinson - Danielsville, GA USA
    Airheads #3480 | Iron Butt Assn. #8914
    1976 R75/6 - 1992 R100RS - 1993 K1100RS - 2013 R1200GS

  3. #3
    Registered User beemermyke's Avatar
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    Lee, would it make any sound if it were the brushes?
    Motorcycling is my passion because golf is far too dangerous!
    2016 R1200GSW

  4. #4
    Quote Originally Posted by beemermyke View Post
    Lee, would it make any sound if it were the brushes?
    No, I missed that. Could be bearings then.
    Lee A. Dickinson - Danielsville, GA USA
    Airheads #3480 | Iron Butt Assn. #8914
    1976 R75/6 - 1992 R100RS - 1993 K1100RS - 2013 R1200GS

  5. #5
    Registered User kioolt's Avatar
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    Pull the alternator off and check the coupling between the alternator and the engine. It's not hard to pull off. It may save you from replacing the whole alternator.
    2004 R1150RT 186,800 miles , 1991 K100LT 128,700 miles, 1982 R100RT 106,900 miles
    Total 422,400 BMW miles
    AMA,BMWRA,BMWMOA
    The cheapest thing on a BMW is the nut that connects the handlebars to the seat.

  6. #6
    Quote Originally Posted by kioolt View Post
    Pull the alternator off and check the coupling between the alternator and the engine. It's not hard to pull off. It may save you from replacing the whole alternator.
    Brushes would not cause a very loud rattling noise, but could cause it to stop charging. Deteriorated coupling dampers could cause some loud racket, but would it cause it to stop charging?.

    alternator k1100.jpg

    Next step is definitely to pull it. Then he can check the coupling, bearings, and brushes. Most likely, repair will be a better alternative than replace. An auto parts store might be able to spin it up and check output.
    Lee A. Dickinson - Danielsville, GA USA
    Airheads #3480 | Iron Butt Assn. #8914
    1976 R75/6 - 1992 R100RS - 1993 K1100RS - 2013 R1200GS

  7. #7
    Registered User beemerguru's Avatar
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    Alternator issues

    If the alternator rubbers have completely deteriorated, then it's metal on metal and the vanes WILL wear down so far the alternator won't spin...then you need to replace the cup as well as the rubbers.
    Greg Hutchinson
    R80G/S (4) 633CSi with 450K mile
    '68 R60/2 '88 K100RS Special Edition
    http://gregsgssite.shutterfly.com/

  8. #8
    Thank you all for your Input. I ordered a new alternator and rubber bushings from euroelectrics.

  9. #9
    My new Euroelectrics alternator is installed and now im getting odd voltage readings. At idle, my voltage reading is 12.2v. I have a steady climb in voltage until it peaks at 14v at 4000 rpm. Is this normal ? I wasn't sure if these bikes have a voltage attenuator that should keep the voltage constant at 13.5v

  10. #10
    It should charge sooner than that. The voltage regulator is built into the alternator. Are you starting with a well charged battery?
    Lee A. Dickinson - Danielsville, GA USA
    Airheads #3480 | Iron Butt Assn. #8914
    1976 R75/6 - 1992 R100RS - 1993 K1100RS - 2013 R1200GS

  11. #11
    Registered User beemermyke's Avatar
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    It's a three month old Oddysey battery and the charge was good and cranked strongly. Talking to the previous owner, he says that the voltage fluctuation between idle and higher RPMs was a known issue on the older bikes. We don't really know that much about the older bikes which is why the OP posted the question last night.
    Motorcycling is my passion because golf is far too dangerous!
    2016 R1200GSW

  12. #12
    Quote Originally Posted by beemermyke View Post
    ...Talking to the previous owner, he says that the voltage fluctuation between idle and higher RPMs was a known issue on the older bikes.
    This is the same Bosch alternator used in the oilheads. I don't recall that tendency on any of my oilheads or K's. I have changed the voltage regulators inside the alternators to get 14.2 volts instead of 13.8 to better suit AGM batteries, but they have all charged strongly from 1500 revs. If by "older bikes" he means airheads, then yes, they were known for that but that is a completely different technology. K's? I haven't seen that.

    With a good battery, and now two alternators, the behavior is pointing towards connections. I would check ground resistance from the battery strap to the central ground under the tank. While at it, I would clean, de-ox, and reattach the grounds. I never did hear a follow-up on where the noise was coming from. How did that resolve?
    Lee A. Dickinson - Danielsville, GA USA
    Airheads #3480 | Iron Butt Assn. #8914
    1976 R75/6 - 1992 R100RS - 1993 K1100RS - 2013 R1200GS

  13. #13
    Registered User beemermyke's Avatar
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    The noise is gone (sorry for the lack of follow-up, it's been parked awhile due to work commitments). We checked the voltage at various RPMs this morning to see what the differences were. At idle, 12.4V, 1000 RPM, 13.3, 1500 RPM, 14.4. Since my son Bwoods1100 put this bike together from a basket case and didn't have much to go on, we'll recheck battery strap, etc. and clean things up as needed.
    Motorcycling is my passion because golf is far too dangerous!
    2016 R1200GSW

  14. #14
    Quote Originally Posted by beemermyke View Post
    The noise is gone (sorry for the lack of follow-up, it's been parked awhile due to work commitments). We checked the voltage at various RPMs this morning to see what the differences were. At idle, 12.4V, 1000 RPM, 13.3, 1500 RPM, 14.4. Since my son Bwoods1100 put this bike together from a basket case and didn't have much to go on, we'll recheck battery strap, etc. and clean things up as needed.
    Those voltages are fine. 14.4 at 1500 is all you should expect.
    Lee A. Dickinson - Danielsville, GA USA
    Airheads #3480 | Iron Butt Assn. #8914
    1976 R75/6 - 1992 R100RS - 1993 K1100RS - 2013 R1200GS

  15. #15
    3 Red Bricks
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    12.4v means that your battery is not fully charged.

    Your idle speed is also too low. Should be 1000-1050 rpm.



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