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Burnt Exhaust Valve? Need advice

Discussion in 'XJ Technical Chat' started by maximusprime, Jan 18, 2016.

  1. maximusprime

    maximusprime New Member

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    Hi everyone, so here's the story:

    I was riding my 1982 Maxim 650 from Portland to the Grand Canyon when both of the nuts that hold on one of the exhaust pipes broke clean off (They must have been over-tightened). This pipe was then hanging loose with a gap between it and the engine. I would've dealt with it right away but I had to make it to the Canyon for a rafting trip, so I rode it from Chico to Flagstaff with a loose exhaust pipe.

    I've read that this can cause the exhaust valve in that cylinder to burn when cold air comes in to the cylinder and causes some leftover gas to burn in the exhaust cylinder. The bike was indeed running rough when I finished the trip. I had to give it some throttle to even get it to start.

    Do you have any experience with this? Do you know of any good resources for learning how to replace the valve? Do you think this diagnosis is correct?

    Thanks
     
  2. tabaka45

    tabaka45 Well-Known Member

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    Before you do anything I would do a compression test. That should let you know if you have a burnt valve. My bet is that you didn't do any damage and that the broken pipe and lack of proper back pressure is causing the rough running.
     
  3. k-moe

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

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    Burning a valve because of an exhaust leak is unlikely (let me tell you about the truck I ran for three years with a exhaust manifold that was only hanging from three studs).

    Could you share your maintenance history with the bike?
    When as the last time the vlave clearances were checked? Carbs cleaned?
    Did you ride through wet weather before it started running rough?
    Did it happen to start running rough shortly after filling it with gas?
    Is the oil level correct?
     
  4. maximusprime

    maximusprime New Member

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    Thanks guys,

    so I got it in good shape with only 10,000 miles on it and the only maintenance I did was change the oil and brake pads. I took it cross country before this trip and during that the oil light went on and I had to add a bunch. I figured it was burning oil because I was running for hours at 6-7k rpms. It was probably low again when this happened. I believe the carbs and valves were ok because the issues didn't start until the exhaust pipe came off. I wonder if the back pressure could be the issue. I don't really know anything about that. It did seem to get somewhat worse as I rode from chico to AZ. I didn't hit any rain after the pipe came loose.
     
  5. k-moe

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

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    So you rode a 33 year old motorcycle on a cross-country trip without doing any of the catch-up maintenance?! You are brave.

    Time to stop being brave.

    Have a read.

    The Information Overload Hour

    The Real Costs of Maintenance


    FYI: I go on multi-day tours in the summer, running all day at 70 to 80 MPH. I rarely have to add oil.

    I think a compression check is in order, but only after you check valve clearances. They should have already been checked twice when you bought it, but most likely never have been.
    If anything burned a valve it was improper clearances, not the loose header.
     
    Last edited: Jan 18, 2016
  6. hogfiddles

    hogfiddles XJ-Wizard, Host-Central NY Carb Clinic Moderator Premium Member

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    +1
     
  7. Stumplifter

    Stumplifter Well-Known Member

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    What he ^ said.
    Don't do that anymore.
     

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