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Thread: Transmission noisy

  1. #1
    Registered User OLDRIDER's Avatar
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    Transmission noisy

    I have a 1990 R100RT with a transmission that rattles in neutral with the clutch out. The local BMW dealer installed new bearings and seals and shimmed it a second time trying to eliminate the knocking with each firing of the piston, heard after the transmission has warmed from riding. What could this be other than improper shimming? Any ideas?
    OldRider

    "It's always been about Riding"

  2. #2
    James.A
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    What is your idle speed? That kind of noise went away in my R75/5 when I adopted the practice of setting the idle speed above 1000RPM. There is a clue in your statement;"...knocking with each firing of the piston". What you are hearing is the gear sets slapping each other gently at the moment that a cylinder is about to fire and the momentum of motor revolutions gets interrupted. It's almost as if the motor stops for a nano-second before the cylinder fires. Obviously, this would be more pronounced at lower RPMs.

  3. #3
    Bluenoser
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    Did they service the clutch rod and related bearing? If its noisy in neutral and then the noise goes away when the clutch is pulled in, I'd check the throw out bearing on the clutch rod at the back of the transmission. Just take it apart have a look & service it.
    1971 R50/5 SWB with R75/6 drivetrain
    2013 DL650

  4. #4
    Administrator 20774's Avatar
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    Too some degree, most transmissions do that. Once the clutch handle is pulled in, the noise should disappear. Mostly, the better the carb synch, the less the noise.
    Kurt -- Forum Administrator ---> 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!

  5. #5
    James.A
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    The most rattly transmission I ever heard was in an R1100RSL that I purchased new in 1994. I am convinced that this is not abnormal. I agree with Kurt that well synced carbs can minimize the effect.

  6. #6
    Registered User OLDRIDER's Avatar
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    Quote Originally Posted by James.A View Post
    What is your idle speed? That kind of noise went away in my R75/5 when I adopted the practice of setting the idle speed above 1000RPM. There is a clue in your statement;"...knocking with each firing of the piston". What you are hearing is the gear sets slapping each other gently at the moment that a cylinder is about to fire and the momentum of motor revolutions gets interrupted. It's almost as if the motor stops for a nano-second before the cylinder fires. Obviously, this would be more pronounced at lower RPMs.
    I will bring up the idle speed and see if that helps. It will make smoother shifting as well.

    I'll make sure the carbs are synched which I now understand could be part of the problem.

    Thanks for your advise.

    Bob
    OldRider

    "It's always been about Riding"

  7. #7
    Registered User 88bmwjeff's Avatar
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    Quote Originally Posted by 20774 View Post
    Too some degree, most transmissions do that. Once the clutch handle is pulled in, the noise should disappear. Mostly, the better the carb synch, the less the noise.
    My 88 R100 RT does that. I was told that that's normal for these bikes. I don't worry about. Granted I have good used tranny on the shelf just in case. However, given Murphy's famous law, that item I probably not need.
    Jeff in W.C.
    1988 R100 RT (the other woman)
    "I got my motorcycle jacket but I'm walking all the time." Joe Strummer

  8. #8
    Registered User toooldtocare's Avatar
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    I have several bikes that do that, some of them started right after buying new. Even had a car that did that. Always explained it as the gears bouncing around due to uneven firing.

  9. #9
    Benchwrenching PGlaves's Avatar
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    Oak Okleshen explained it this way in 1974:

    "The noise is the result of an unloaded transmission and the backlash in the mating parts clattering slightly due to variances in engine speeds when at idle. The engine, though we think of it as running at a constant speed, varies in a miniscule amount when it is unloaded and at low speeds near idle. This happens between the power pulsations from the pistons. The flywheel helps to prevent the uneveness but does not cure the problem entirely for it would take a much larger and heavier flywheel than necessary to make the machine run properly and would detract from acceleration performance. As a result, the engine pulsates and the transmission attempts to run at a constant speed. Between pulsations the backlash in the transmission causes the components to clank lightly and cause noise.

    The noise can become more noticeable if the carburetors are unbalanced left to right. This causes engine pulsations to become more uneven and, hence, there is more noise in the transmission in neutral, clutch engaged."
    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://www.bigbend.net/users/glaves

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