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Thread: '86 K75T Vibration

  1. #1
    Registered User BBKME's Avatar
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    '86 K75T Vibration

    Recently had my alternator replaced with a rebuilt one. Now the bike has a vibration that wasn't there before. At all speeds but notice it more when @ interstate speed. Feel it mostly through the handlebars but a little in the footpegs as well. It's a rythmic vibration almost like it's in the front wheel so not sure if it's related to the new alternator or just something else?
    Brian
    1986 K75T

  2. #2
    What, me worry? GILLY's Avatar
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    Did you replace the rubber buffers, commonly referred to in KBike circles as the "monkey nuts"?

    http://www.beemerboneyard.com/12311464877.html
    87 K75S, bought new, now sold
    07 K1200GT Bought new, now traded in
    13 C650GT
    MOA 44606

  3. #3
    A bozo on the bus deilenberger's Avatar
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    You didn't do the work?

    A quick test for the alternator being the cause.. cruise along at 70MPH, pull the clutch in and let the engine idle for 10 seconds. Did the vibration go away?

    If so - combined with it just being replaced, I'd suspect it. Things that could cause vibration are - as noted - bad/worn monkey-nuts (you'll understand the term when you see them) or the drive vanes that connect the alternator to the engine not being aligned so they are metal to rubber. That's easy to mistakenly happen. Trick I learned was to use a magic marker to mark the outside of the drive cup on the alternator - where the gap between the nuts is (that the drive vanes are supposed to go in.) You can see the vanes on the drive nubbin, you can't see the ones inside the driven cup (alternator side) when assembling it.. so then you line up the line you made with one of the vanes and it goes together correctly.

    New monkey nuts are usually quite snug. I found using a bit of silicone grease on the slot where they connect to the driving nubbin helps it all side together easily, and the silicone grease helps protect the rubber they're made out of. Win-Win.
    Don Eilenberger http://www.eilenberger.net
    Spring Lk Heights NJ NJ Shore BMW Riders New Sweden BMW Riders
    '07 R1200R (current ride) and some bimmers.. and a Porsche

  4. #4
    Registered User BBKME's Avatar
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    Thanks for the suggestions. I finally got a chance to pull the alternator & check things out. Missing a set of monkey nutz and the two left were pretty worn. Also noticed the gap in one of the sets seems much larger than the other one. Not sure if the size varies among models/years? I did not do the original work myself but wishing I did after realizing how simple it was to pull the alternator. I'm not too happy with the dealer who did the work. I was told that a gas tank rubber mount fell into the alternator and melted all over causing the alternator to fail. I'm guessing it was just one of the nutz that melted and they never bothered to replace it or the other two sets. Going back to the dealer to try get some money back but that will be the last visit to that place for service.
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    Last edited by BBKME; 12-03-2012 at 05:19 PM.
    Brian
    1986 K75T

  5. #5
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    Check this tread.

    http://www.bmwmoa.org/forum/showthre...ht=monkey+nuts

    Check this thread. It looks like you have one genie BMW monkey nut and one after market monkey nut. The first picture in the thread shows the genie BMW in the upper right and the lower right in your picture. Harold in Kansas
    Harold In Kansas
    1985 K100RT Bullit
    1985 K100XX/EML Bemel

  6. #6
    Registered User BBKME's Avatar
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    Thank you, Harold.
    Brian
    1986 K75T

  7. #7
    Registered User BBKME's Avatar
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    Thumbs up

    Got the OEM nutz earlier this week and put things back together yesterday. The bike now runs as it should. Smooth as silk again. Many thanks for the advice. It proved extremely helpful.
    Brian
    1986 K75T

  8. #8
    What, me worry? GILLY's Avatar
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    No problem, glad it's all silky again. Hard to find a dealer or non-dealer who really knows a lot about brick engines. Am thinking I should get one again just because I know a little too much
    87 K75S, bought new, now sold
    07 K1200GT Bought new, now traded in
    13 C650GT
    MOA 44606

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