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Valve Stems Broken?

Discussion in 'XJ Technical Chat' started by robvoisea, Sep 9, 2015.

  1. robvoisea

    robvoisea Member

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    1981 XJ 550 Seca; 25,455 miles.
    There is the pretty loud sound coming from the exhaust system: first thought, replace exhaust header gaskets -- done. Make sure that header pipes are snug going into collector: done.
    Still the sound persists.
    When the engine idles, nothing. Under acceleration the sound is very loud (as I said, initially I thought it was an exhaust leak).
    Another indicator: performance, I can twist the throttle all the way and she has a hard time getting to 80mph.

    What am I missing?
    Tonight, I'll take the valve cover off to see if things are flying around in there.

    Any suggestions? Any similar experiences?

    Thank you for the feedback
     
    robvoisea, Sep 9, 2015
    #1
  2. MN-Maxims

    MN-Maxims St. Paul Minnesota

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    Bent rod, loose crank bearings , pistons hitting the head. Defiantly look at the cams first. Check the cam chain to see how loose it is.
    A compression test may clue you in if you have one cylinder acting up.
     
    MN-Maxims, Sep 9, 2015
    #2
  3. robvoisea

    robvoisea Member

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    Thx.
    Looks like a nice top end overhaul ...
     
    robvoisea, Sep 9, 2015
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  4. k-moe

    k-moe Pie, Bacon, Bourbon. Moderator Premium Member

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    Is the bike running lean?
     
    k-moe, Sep 9, 2015
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  5. robvoisea

    robvoisea Member

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    Not running lean; I switched from synthetic oil back to conventional but that sound was already there when I was running synthetic.
    My goal is to use conventional oil and change it once a month.
     
    robvoisea, Sep 9, 2015
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  6. MN-Maxims

    MN-Maxims St. Paul Minnesota

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    Engine knocks can be hard to diagnose when you are not sure where its coming from. My cam chain was loose on my 1100 and was slapping around in there but is not real loud. I went through and did the adjustment procedure and it cleared up.
    Some bikes have automatic chain adjusters on them but I'm not sure if the 550 does. A lean condition can score a piston but that should show up on a compression test and it would only be running on three cylinders. Lets hope that's not the case. Let us know what you find.
     
    MN-Maxims, Sep 10, 2015
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  7. robvoisea

    robvoisea Member

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    The Seca has an automatic cam chain adjuster.
    I am really nervous taking a look under the valve cover (no time this weekend, will update as soon as a I find the courage to do this).
     
    robvoisea, Sep 10, 2015
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  8. MN-Maxims

    MN-Maxims St. Paul Minnesota

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    In any case good luck and hope it is nothing to drastic to fix.
     
    MN-Maxims, Sep 10, 2015
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