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Compression Question -- Stuck Rings?

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  • Compression Question -- Stuck Rings?

    Hi all, I have a 1972 85HP Chrysler that I just put on my boat. The history on the motor is a little vague but I know that it has been sitting indoors for around 10 years. I squirted a small amount of WD40 inside the cylinders before turning the flywheel by hand to lube the cylinders a bit. This was on Friday. On Saturday I finally got it put on my boat and got it hooked up and decided to check the compression. There readings were as follows:#1: 126#2: 100#3: 130 I know the guidelines about no more than 15psi between cylinders. What I'm wondering is if it is possible to determine if this variation on #2 is from stuck rings due to sitting for an extended period? I can't run the engine because I believe it has a bad CD module, so I can't decarb and retry. However, if it isn't stuck rings, I don't want to put the money out to buy a CD module.Any suggestions?Thanks,Shane


  • #2
    Re: Compression Question -- Stuck Rings?

    You could pull the head and visually inspect the bore & piston, or pour decarb directly into the bores through each spark plug holes with the engine tilted up. You'd have to soak each piston raised individually so that the ports are cut off and the decarb doesn't run out.Hope this helps!

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    • #3
      Re: Compression Question -- Stuck Rings?

      Hi Paul, Thanks for the reply. Could you explain the process a little more of pouring decarb directly into the cylinder and then letting it sit? Well, that's kind of self explanatory but how would you get it and the carbon out with the engine not running? Also what do you mean about raising each piston so the ports are cut off? I'm a little confused. By doing this would it soak through so as to free up the rings?ThanksShane

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      • #4
        Re: Compression Question -- Stuck Rings?

        Hey Turtle,Get rid of the WD40. It's not a lubricant or penetrating oil. It use to be pretty good starting fluid for 2 strokes but it's not even any good for that anymore.Give each cylinder two or three squirts of 50:1 outboard oil and with a good, hot battery and the carburetors open, check the compresson again. If you still have the one cylinder low, either remove the head and examine it or pop for the ignition module, light the thing off and see how it runs. The compression will come up when it's warm. You may need to do a decarb job or run it as is.c/6Hooty

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        • #5
          Re: Compression Question -- Stuck Rings?

          Sorry, I wasn't being very clear. The idea is not to clean the carbon out of the cylinder, but simply to loosen the rings (if they are stuck) so they contact the cylinder wall, hopefully raising compression.1) Label all plug wires and remove all spark plugs.2) Raise the engine so the spark plug holes are pointing to the sky.3) Stick a pen down the first spark plug hole (Don't drop it!) and rotate the engine until the pen pushes all the way up (This is not critical).4) Pour in a little Decarb fluid into the cylinder.5) Wait a couple hours... While waiting turn flywheel slightly (10 degrees or so) back and fourth to help loosen the rings (hopefully).6) Get decarb solution out. A turkey baster works if you used a lot. Probably skip this step if you used a teaspoon (you got the engine perfectly horizontal).7) Go to the next cylinder and repeat from step 3.You'll probably want to try #2 only.PS - 2 stroke engines, unlike 4's, have holes or grooves in the side of their cylinders near the bottom. It's through these holes that gas gets in from the crankcase and exaust out. They are cut off by the piston as it moves higher in the cylinder & compression starts. If you dumped decarb solution into a cylinder where the piston is at the bottom, it would simply run out the holes or down the grooves.Hope this helps!

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          • #6
            Re: Compression Question -- Stuck Rings?

            Hooty, Thanks for the advice about WD40. I won't use that anymore for anything other than squeaky doors It seems like I read somewhere that putting premix (or any lube) into the cylinder will give a false compression reading because it temperarily seals whatever the problem might be. Have you heard anything like that or is it just my imagination? I'm not saying its a bad idea. I'm just asking because I don't know.Paul, Thanks for the clarification and further explanation. Will seafoam work for this? That's the only brand I can think of that is here locally. After the solution has set, would it be bad just to rotate the flywheel and let the decarb go out the exhaust manifold or do I need to manually remove it.Thanks guys!Shane

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            • #7
              Re: Compression Question -- Stuck Rings?

              Turtle - No problem. Seafoam is what I was thinking of. If you rotate the flywheel to dump the decarb, you'll have to be careful. The exhaust ports open *just* before the intake ports. If the seafoam does loosen up much carbon, you wouldn't want it flowing into the crankcase where it'll get into the bearings. Personally, I wouldn't even attempt it.

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              • #8
                Re: Compression Question -- Stuck Rings?

                It's true, oil in the cylinders will usually give a higher compression reading than if the cylinders were dry, but, when the engine is running, the cylinders are lubed with the oil from the fuel, so what you're seeing when you check the compression with oil in the cylinder is more indicative of what's taking place when the engine is running.c/6Hooty

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                • #9
                  Re: Compression Question -- Stuck Rings?

                  Paul, Personally, you wouldn't attempt the entire procedure or you wouldn't attempt rotating the flywheel? Just looking for clarification. Also, how much seaform should I put into this cylinder? Fill it up or just a teaspoon?Thanks again,Shane

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                  • #10
                    Re: Compression Question -- Stuck Rings?

                    Hooty, Thanks for the explanation. That actually made sense I'll give that a try first thing in the morning.Shane

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                    • #11
                      Re: Compression Question -- Stuck Rings?

                      Hi Turtle Both Hooty and Paul are telling you true. I would go more with Pauls suggestions if you had less compression in that #2 hole. Since you have to strong holes and you still have a 100psi in the weekest one. I am going to vote with Hooty. Once you fire the thing up and warm it up a little the compression should even out a little. I have brought motors back to life that had no measurable compression on any cylinder using Pauls method. Your not in that bad a shape here.

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                      • #12
                        Re: Compression Question -- Stuck Rings?

                        I wouldn't attempt dumping the seafoam out the exhaust ports. Enough seafoam to cover the rings ("moat" the piston). It really depends on how close to horizontal you can get the engine. The idea is to submerge on side of the ring in seafoam. Hope this helps! (Sorry for being unclear. It's getting late here)

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                        • #13
                          Re: Compression Question -- Stuck Rings?

                          Thanks again guys. You all are great! When I checked the compression last night my heart sunk when I saw that lower reading. But the more I thought about it, the more it seemed like it might not be such a serious issue. But I wanted a little insurance before forking out some money for the CD module. Shane

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