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Compression Dilemma!

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  • #1

    Compression Dilemma!

    Tested the compression on all cylinders today. Man what a surprise. The resulst are as follows:

    No. 1 - 93psi.

    No. 2 - 91

    No. 3 - 88

    No. 4 - 95

    No. 5 - 94

    No. 6 - 91

    Clymers states that compression should be 110-120psi, with a max variation of 15psi between cylinders.

    Do you think with the numbers being as consistent as they are and not having any true symptoms of engine trouble that I might have faulty calibration on the guage?

    How about a little chime in here. Do you guys think I have anything to worry about? It is a '94 (Merc. 225, 3.0L Carb.) without ever being overhauled. Do you think she's getting tired. Am I looking at major trouble in the near future or am I just getting paranoid.

    In advance, I appreciate your input.
    Justus[br]\'93-211 Classic [br]Baton Rouge
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  • #2
    Not really. When is the last time you gave it a good douching with Ring Free? That will get the carbon out of the ring lands and maybe jump your number's up a little.

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    • #3
      Since I have the Merc Shop manual opened on my desktop... Heres what it says:

      Compression: 90-110 psi (not more than 15 psi variance between cylinders)

      You are in pretty good shape. Alot depends on your gauge. I have an el cheapo gauge and it read 10 psi less than the good Snap On gauge that the mechanic shop that bought my Yamaha used. What kind of gauge are you using anyway?

      I would look ino a good round of Ring Free. The stuff is pretty good.
      Slidell, LA 1993 Mako 261B - Temperance

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      • #4
        I believe your fine. Those numbers wouldnt worry me at all. Like Bobby said use the ringfree. Compression gauges vary all over the place. At 12 years old though I would consider turning it into a premix engine if you havent done so already. 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.

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        • #5
          Thanks guys for the input. I have never used Ring Free. I have douched it occasionally with the Merc. Power Tune aerosol stuff. If you all are that confident about the Ring Free then i'm jumping on it. Where do you get it and what's the process for use?

          Hey Eddie, I wonder why the variation between Clymer's and the shop manual you referred to? The Clymer's numbers is what really made me think I was preparing for an outboard funeral. By the way, the guage I used is a relative cheapo ($25)from Harbor Freight. I'm going to bring it to an instumentation shop soon to check its accuracy. Anyway, thanks for the chime in guys I feel a little better now.
          Justus[br]\'93-211 Classic [br]Baton Rouge

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          • #6
            Justis I wouldnt wast your cash on getting it checked. the important thing here is that there all within 15% of each other. The Merc. power tune is as good as the ring free. These newer motors do not have the high compression of the days of old. This enables us to use the lower octain fuels. Again I would consider changing it over to a premix engine if you havnt done so already. 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.

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            • #7
              Justus-

              I think your are fine. The most important thing is that all the cylinders are within 7PSI of each other. You can take one motor and do compression tests with 3 different testers and you would get 3 different readings. I also have been told that the compression will be different if you do it before and after running the engine.

              As Bobby mention, I would just make sure you clean her out and you should be okay.

              Ed

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              • #8
                Sounds great, Thanks again fellas!
                Justus[br]\'93-211 Classic [br]Baton Rouge

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                • #9
                  Justus, just curious, before doing the test, did you get the motor up to operating temp? and give it wide open throttle when cranking the engine? By NOT doing what i stated, you'll get lower #'s
                  [br]Michael R. Delgado[br]1972 Mako 22[br]http://classicmako.com/forum/topic.asp?TOPIC_ID=15745[br]1976 Mako 25[br]http://classicmako.com/forum/topic.asp?TOPIC_ID=18013&SearchTerms=mako,25[br]

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                  • #10
                    mrdelgado is exactly right.

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                    • #11
                      I have a question about switching it over to pre-mix. Why? I have an older than 12year Suzuki 150 motor should I consider switching over?
                      Dave[br]Monument Beach, MA

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                      • #12
                        The oilers in the motors have a tendency to go out after a few years of service. You can switch to premix or get a new oiler pump. When they go out... they never give you any advanced warning... they just go out.
                        Slidell, LA 1993 Mako 261B - Temperance

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                        • #13
                          In response to MrDelgado and Warthog, I did in fact run the engine for about 10-15 mins and tested at WOT. I don't know if I was as operating temp though, because I was surprised when removing the plugs that I could hold them with bare fingers. In other words although they were quite warm, they weren't super hot. I thought that they would be scroching hot.
                          Justus[br]\'93-211 Classic [br]Baton Rouge

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                          • #14
                            Hey Ring, what brands of motor do you see this happen on? you're scaring me! Mine is a 1987 200 zuki, but looking at the manual, the oil pump looks really simple, like an automotive oil pump (2 gears meshing). what part of it usually gives out?
                            [br]Michael R. Delgado[br]1972 Mako 22[br]http://classicmako.com/forum/topic.asp?TOPIC_ID=15745[br]1976 Mako 25[br]http://classicmako.com/forum/topic.asp?TOPIC_ID=18013&SearchTerms=mako,25[br]

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                            • #15
                              Mr D,

                              You will see that on pretty much all motors that have injection...Dont think it is brand specific. My OMC actually had the VRO pump go bad and start putting too much oil in. That was much cheaper than the alternative.
                              Greenwich, NJ[br]1976 22B

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