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  1. #1

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    This compression is good

    Hello today in a compression test on my msx 140 2003, the 3 piston 115 lbs. compression and the information I have is that you must have Standard -120-150 lbs. / sq. in this good or not no


  2. #2
    Click avatar for tech links/info, donation request K447's Avatar
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    What are the other two cylinder's compression?

  3. #3

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    all scored 115 lb cylinder

  4. #4
    If all 3 are 115psi then you should be good to go. Keep on riding!!!!

  5. #5

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    We must change the pistons rings to have the correct compression of 120 ps to 150 ps or should I leave like this to 115 ps

  6. #6
    Click avatar for tech links/info, donation request K447's Avatar
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    Are you sure your measurements are accurate?

    When testing compression, all spark plugs must be removed, and the throttle held wide open.

    You 115 numbers are low, but with all three being very close together, it may just be a measurement error, not an actual problem with the engine.

  7. #7

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    Ok I experimented with removing the spark plugs one by one, I'm going to redo the test with all spark plugs disconnected then inform you what are the new reading of compression

  8. #8
    Connecticut CrazyA's Avatar
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    Freddy,
    Make sure you hold the throttle wide open when cranking like K447 said.

  9. #9
    Connecticut CrazyA's Avatar
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    Quote Originally Posted by K447 View Post
    Are you sure your measurements are accurate?

    When testing compression, all spark plugs must be removed, and the throttle held wide open.

    You 115 numbers are low, but with all three being very close together, it may just be a measurement error, not an actual problem with the engine.
    We always say this, but Group K says this:

    THE ENGINE - 1) All accurate readings must be taken from a dead cold engine. A warm engine will yield slightly lower numbers. 2) The exhaust pipe and carburetor must be installed. The restrictions in the carb throat and the back pressures of the exhaust system can affect the readings. 3) Have a full charge on the battery. The speed that the engine is spun, has a significant affect on the indicated reading. Having the charger connected during the test insures maximum starter motor RPM's. 4) Leave a spark plug in the cylinder not being measured. Contrary to what you may think, the engine will turn over slightly faster with the opposing spark plug installed.

    I've never done a back-to-back test. Any thoughts?

  10. #10

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    Quote Originally Posted by freddypr1 View Post
    Ok I experimented with removing the spark plugs one by one, I'm going to redo the test with all spark plugs disconnected then inform you what are the new reading of compression
    I do the compression test again as I am informed


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