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  1. #1

    Join Date
    Jul 2006
    grand bend.

    compression woes?


    I compression tested my stage 2 gpr last evening and ended up with 120, 120, 115. This would be good for a stock engine but I have a milled head. I added oil to cylinders #1 & 2 and the readings increased to 130. I had the same results with the pv's wired open & closed. Is this normal? I trust the compression guage as I tested my friends 07 gpr and it pulled 130,130,125. Without pulling it apart, I am assuming that my rings are worn after 93 hours and need to be replaced. Is it ok to replace the rings without new pistons? Do I need a ring compressor and/or expander? The cylinders looked mint when I put on the new head and you could still see the factory hone marks. Would 600-1000 grit sandpaper with 2 stroke oil be a good way to clean them up?


  2. #2
    Hydrotoys's Avatar
    Join Date
    Jul 2005
    Mesa, AZ
    You would probably be incorrect to jump to that conclusion.

    You coud have a bad gauge, a slow starter, or a leaky hose.

    About the worse thing in the world you could do is go sandpapering Nikisil cylinders.

  3. #3
    Moderator Insanediego Joe's Avatar
    Join Date
    Mar 2006
    San Diego, California, United States
    You should have 8 to 10 pounds less compression with the valves open compared to when they are closed.

  4. #4
    injected2stroke's Avatar
    Join Date
    Feb 2006
    Taylor Mi.
    I don't think you want jump top the conclusion that your rings are bad just yet you will get a lot more than 93 hours out of them. You need a good gage for sure Snap on is my gage of choice. And it can make a big difference I say 10 psi. Make sure the engine is warmed up, you have only the plug out of the cylinder you are checking, PV closed, and the throttle in the wide open position. Just the fact that you readings look consistant says it's most likely nothing major. Also make sure that you have the hose with the same or very similar length threads as your spark plugs. By the way who did you have do your head?
    Last edited by injected2stroke; 07-20-2007 at 04:33 AM.

  5. #5

    Join Date
    Jul 2006
    grand bend.
    I performed the test on a cold engine, throttle open, pv's closed and the tested cylinder plug out. I have the long reach adapter attached to my guage. I'm scratching my head due to the fact I tested a stock 07gpr with the exact same method and it pulled higher numbers. I did try another battery with the same results. I will try again with the battery hooked up to the charger. I hope it's a slow starter as mentioned. I had my head milled here

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