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Compresson on my 1981 650 Maim.

Discussion in 'XJ Technical Chat' started by vector, Apr 20, 2011.

  1. vector

    vector New Member

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    Just bought a 1981 maxim which was not ran for three years. I gave it a compresson check and found the following: #1 cylinder was 127/ # 2 was 125/ # 3 was 120/# 4 was 135. Before I turned the engine over I shot some peatrating oil into the cylinder and turned it over several times. It has 27000 miles on it. Is this variance exceptable. Would the valve shim adjustment change the compession,or is the engine worn out?
     
    vector, Apr 20, 2011
    #1
  2. ManBot13

    ManBot13 Well-Known Member

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    Those compression numbers look good, they are within 15 psi of each other and above 120 (rule of thumb).

    I'm not sure if the penetrating oil can seal ring leaks like oil can (for testing if low compression is due to valve or cylinder wear).

    You could test again, wide open throttle with TCI disconnected, and "dry" to be sure. If then numbers are the same, then I'd say it's time to move on to other things (like valve clearance adjustment, carb cleaning, tuning etc) :-D

    Congrats!
     
    ManBot13, Apr 20, 2011
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  3. Zookie400

    Zookie400 Active Member

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    as stated above, make sure you comp test with the throttle wide open. if not, you could see differences in numbers due to different amounts of air being allowed into the cylinders before the compression stroke.

    a valve adjustment will only help you if one or more of the valves is tight. if they are out of spec but not to the point of being held open, you shouldnt see much of a difference.

    those numbers are good. mine are way lower :)
     
    Zookie400, Apr 20, 2011
    #3
  4. bigfitz52

    bigfitz52 Well-Known Member Premium Member

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    A valve adjustment could very well bring the numbers closer together, depending on how out of spec the valves are.

    It looks to me like you might have a good starting point there, though.
     
    bigfitz52, Apr 20, 2011
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  5. lostboy2

    lostboy2 Member

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    Those numbers look pretty good. I would move on to other things (carb cleaning, checking brakes both front and rear and replacing fluids) Good luckand glad to see another bike coming on the road.
     
    lostboy2, Apr 21, 2011
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  6. vector

    vector New Member

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    Did all the above and took it for a ride. It ran great. I checked the compression when I got home and the engine was warm and got the following: # 1/142/#2/140/#3/132/#4/142. I took it three times.
     
    vector, May 17, 2011
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  7. wizard

    wizard Active Member

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    try a spoon of oil in #2, see if that reading goes up.
     
    wizard, May 17, 2011
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  8. vector

    vector New Member

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    Do you mean # 3 as that is the lower one.
     
    vector, May 17, 2011
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  9. vector

    vector New Member

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    I just noticed that I left the X out in Maxim. LOL.
     
    vector, May 17, 2011
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  10. wizard

    wizard Active Member

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    whatever.
     
    wizard, May 17, 2011
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  11. vector

    vector New Member

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    Thank you for the info.
     
    vector, May 17, 2011
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