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Thread: One-way chain tensioner? '91 K100RS

  1. #1
    OldAndBusted
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    Question One-way chain tensioner? '91 K100RS

    Hi all, I'm doing valves on a 4v K100RS, they were fairly well out of spec. But while messing around with it, I think I may have let all tension go on the cam chain tensioner while the cams were out. I think I read that the tensioner is a one-way ratchet. The chain and sprockets sure are damn tight now when trying to get them back on the cams. Am I gonna have to open up the cam cover and mess with that ratchet mechanism to loosen it up again and reassemble it all? Anyone familiar with this stuff?

    Thanks.

  2. #2
    Registered User mneblett's Avatar
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    Quote Originally Posted by OldAndBusted View Post
    Am I gonna have to open up the cam cover and mess with that ratchet mechanism to loosen it up again and reassemble it all? Anyone familiar with this stuff?
    Removing the lower cam cover access panel is a normal part of removing the cams.

    As I recall (and someone will correct me if I'm wrong) the K100 4V cam chain tensioner arrangement is the same as the K12LT/RS arrangement. The piston for the adjuster is in a hole parallel to the timing chest cavity wall. The tensioner is not a ratchet; it is spring-loaded (with hydraulic support, too, IIRC).

    Basically, you depress the piston inward and insert a pin into the small transverse hole to hold the piston back. That takes the tension off the chain.

    Mark Neblett
    Fairfax, VA
    #32806

  3. #3
    A bozo on the bus deilenberger's Avatar
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    Hi OldandBusted!

    Please read: http://www.bmwmoa.org/forum/showthread.php?t=46057 - it would be quite helpful to know year/model of your bike (and to have it in the thread title..)
    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
    OldAndBusted
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    My bad! 1991 K100RS. I had worked on newer brick engines, LT I think, where the tensioner was movable by just pushing on it with a big screwdriver, like the one blett posted. But this one feels different, doesn't want to move...

  5. #5
    Rally Rat
    Join Date
    Sep 2007
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    1,248
    If you pulled the cams without blocking the tensioner-there's a special tool for this-you'll have to remove the chain cover and tensioner and "wind" it back in. Marrk the hall sensor plate location so you don't have to reset the timing.

  6. #6
    OldAndBusted
    Guest
    Damn, that's what I was afraid of. Thanks for confirming, though.

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