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  1. #1

    How do I check compression?

    I have a compression gauge and have checked compression on my old 2 stroke GP1200. Looks like I need a differant adapter for the spark plug hole though on the RXP--the plug is smaller. Couple questions:

    What size (diameter and thread pitch) are the spark plugs for the Rxp, so I can get the correct size adapter for my compression gauge?

    To check compression do I just hold the throttle wide open and crank for a several seconds like with a 2 stroke?

    For a motor with a ported and decked head and racing cam, what should the compression be roughly?

    If the compression is good would a leakdown test be neccessary to verify engine integrity. I don't have the proper tools for that test.

    Just want to make sure everything is ok before I slap a C kit on in the spring. Engine only has around 130 hours on it.

    Thanks for the input.


  2. #2
    JESUS G's Avatar
    Join Date
    Jun 2007
    South Florida
    There are a good tool from BRP to messure the leaks. Now i dont remember whats the brand but is for 4 tec engines from BRP. Four use it the better is take off the rocker arm shaft and then you have the valves closed. The gauge must to be at 0 for a good condition of the engine. If you have more then , maybe you have a leak in the valves, in the ring etc....

    For the compresion you can use a toll like in 2 strokes but you need to do an adapter.

  3. #3
    Bought a new compression gauge and adapters today. I checked compression and it was 135#. Is that normal for my setup?



  4. #4
    Moderator The Bandit's Avatar
    Join Date
    Jul 2006
    Wilmette, IL
    With the RR cam that is exactly what it is supposed to be.

  5. #5
    Site Admin Green Hulk's Avatar
    Join Date
    Apr 2005
    Morgan City, LA
    Quote Originally Posted by Mark S View Post
    Bought a new compression gauge and adapters today. I checked compression and it was 135#. Is that normal for my setup?


    135 is right on the money. Happy New Year Mark!

  6. #6
    Thanks for the replies. Happy New Year to you all!

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