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Compression Test Help?

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  • Compression Test Help?

    Can anyone provide me with the method for a reliable compression test. I have the guage, but have never done the test before. I would really appreciate a little walk through on the process. Thanx in advance. ('94 Merc. 225 Offshore Carb'd).
    Justus[br]\'93-211 Classic [br]Baton Rouge

  • #2
    1. Run motor for 5-10 minutes to get her warmed up.

    2. Remove all 6 spark plugs

    3. screw compression gauge into cylinder

    4. Open throttle (out of gear) to WOT

    5. Hold key for 4-5 compression cycles

    6. Check number and move to the next cylinder

    All numbers need to be within 10% of each other. I'm not sure what the optimal compression for your motor should be. Probably somewhere around 110 psi, but again, not sure.
    Slidell, LA 1993 Mako 261B - Temperance


    • #3
      Having trouble or just want to know?
      [br]***[br]\'82 Ski Nautique - Lake Martin, AL[br]\'80 236IB - Lake Martin, AL[br]\'03 Pursuit 2670 - Destin, FL


      • #4

        Thanx for the info on the procedure. You are right on the money on the numbers. Clymer's states that compression should be 110-120psi, with a max variation of 15psi between cylinders. I want to check out the ole beast this weekend and see how she's holding up. I have the annual GI trip coming up soon and feel more comfortable heading 30 mi. out knowing she's healthy.

        Man, I hated missing you guys on the trip this past weekend. I have to congratulate you a the rest of the gang for what appeared to be a successful inaugural event. I can only imagine that you all learned a few tricks to make future events that much better. Just hope that baseball, cub scouts and school fairs don't snag me for the next one.
        Justus[br]\'93-211 Classic [br]Baton Rouge


        • #5

          Appreciate the concern, but mostly checking for a little peace of mind for a fairly strenuous (enginewise) upcoming annual trip. I fish a tournament every year with a few buddies out of Grand Isle, LA, and just want to see is she's healthy for the outing. She's getting a little old and am just looking to see if she's also getting tired. We usually run all day up to 30 miles out for about three days straight. On only one engine I am just trying to anticipate any potential problems in advance. She's been a great engine with zero major problems and I keep saying that I intend to run her till she dies. I just don't want her to die @ 30 miles offshore.
          Justus[br]\'93-211 Classic [br]Baton Rouge


          • #6
            The only change I would make to the above procedure is to disable the ignition while cranking. You can do this by pulling the safty lanyard off the kill switch. Otherwise you have spark and fuel at the head area. I only had a problem one time and it was a little exciting. dave.
            [br]1994 Mako 215 Dual console Optimax 225[br]1978 Mako 19 with 90hp johnson[br]1996 Mako 22[br]1982 Mako 171 Angler 135 Black Max Mercury[br]1987 21b 225 Yamaha[br]1974 23 inboard Gusto gone.[br]1979m21 225johnson \"blue dolphin\" bought off this board and restored [br]with everyone\'s help!!Gone but not Forgotten....[br]1979 20 Mako 115 Suzuki gone[br]1977 19 Mako 115 Johnson gone[br]1976 23 Mako twin 140 Johnsons gone[br]1983 224 with closed transom and bracket[br]And 162 SOB (some other boats)[br]Venice Florida, Traverse city Mi.