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Thread: airhead clutch throw-out rod run-out tolerances

  1. #1
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    Apr 2009
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    airhead clutch throw-out rod run-out tolerances

    Hi MOA,

    a fellow member and I are working on his 1980 R65 which
    has a nasty clutch problem where the clutch disengages
    at different places and too quickly. We are trying to determine
    if the problem is his throw-out rod having a 0.002 inch
    runout.

    example: You are stopped at a light and try and slowly
    easy out the clutch handle to engage the 'friction zone'
    and ease out into traffic. Usually it is nothing, nothing
    nothing, nothing, --BAM the bike jumps forward (and
    often stalls). Then from 1st to 2nd the problem isn't
    as bad since you are going. Then other times at a
    light it lets off more smoothly (though still too quickly
    for taste) and all is well.

    The clutch never slips and always engages properly,
    problem is limited to releasing. So we adjusted
    everything from the handle to the cable to the
    arm in the back of the transmission with no relief.

    Became suspicious of the throw-out rod.

    Last weekend we removed the transmission and
    took out the rod for inspection. It does look a
    little worn (flattened) at the tip. We also noted
    in the Clymer manual that they say to check
    for runout with a glass plate and a feeler gauge.
    Well, his has about a 2 thousandth of an inch
    bulge in the middle. Is this within spec ? We
    thought we had found the source of the problem
    and ordered a new one through maxbmw -- but
    it just arrived and has about the same runout.

    Hoping someone can provide first hand experience
    on how straight this rod needs to be, and/or
    if you think the problem might be something else.

    thank you !

    -kai

  2. #2
    Registered User
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    This problem is more than likely excessive end play in the gearbox input shaft. This was common on 79-80s, especially in the R65.

  3. #3
    Registered User gertiektn's Avatar
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    Aug 2009
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    Ketchikan, Alaska
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    check the splines.

    spline need inspection and maintenance???
    I like good stuff. No Chains here!
    1960 R50 -"Hanz"
    1977 R75/7 -"Gertie"
    2004 R1100s -"RFAR1"

  4. #4
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    Quote Originally Posted by lostboy View Post
    This problem is more than likely excessive end play in the gearbox input shaft. This was common on 79-80s, especially in the R65.
    interesting. Are you talking about the splined input shaft ? I'll have a look
    at that.

    Someone else suggested that the piston and bearings were a likely culprit.

    -kai

  5. #5
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    Quote Originally Posted by gertiektn View Post
    spline need inspection and maintenance???
    splines look good, but will definitely be putting it back together fully
    cleaned and greased.

    -k

  6. #6
    Registered User
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    Sep 2007
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    1,248
    Yes, the splined input shaft. If you'd rather not disassemble the 'box to check this, you can put a dial gauge on the cover end of the shaft and warm the cover, then push up and down on the shaft. Spec is .05mm or .002") If it's more than that, you've found the problem.

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