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New Mercury 350 motor w/ hole in piston

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  • New Mercury 350 motor w/ hole in piston

    I have two new 350 crate engines I just installed in my boat last year. I have 19 total running hours. Only two from this year before suddenly losing an engine the other day running at 3300 rpms. #6 piston has a hole in it and everything else is like new. no damage to the head, all carburetor screws intact, valves look great. The engine was running great and timing was set correctly. Has anyone else seen this? Any guesses what might cause this?

  • #2
    Re: New Mercury 350 motor w/ hole in piston

    Running lean or timing too far advanced will blow a hole in a piston. Was it rattling or pinging?

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    • #3
      Re: New Mercury 350 motor w/ hole in piston

      Timing was dead on. If anything the boat was running a little rich at idle. All other pistons look fine. If lean usually the end piston would show the problem I would think. I didn't hear any noise just a lot of smoke.

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      • #4
        Re: New Mercury 350 motor w/ hole in piston

        mmmI wonder how many versions of the 350 CID chevolet made.
        timing for cyl 1 can be dead on,did you ever check 6? crossfiring can occur.
        about the only thing that melts holes in piston is detonation or a lean burn.
        lean burn can come from vacum leaks low fuel pump pressures,all sorts of stuff.
        detonation or preignition can be caused by many things as well.
        what is a crate motor, I usually install marinized motors.
        never tried to repower a crate .
        no tech questions by PM, they wont get answered.
        you have to be trusted by the people that you lie to .

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        • #5
          Re: New Mercury 350 motor w/ hole in piston

          Ayuh,... just a Dirty fuel filter can be enough to detonate a motor....

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          • #6
            Re: New Mercury 350 motor w/ hole in piston

            The only timing that was checked was on one using a timing light and the factory marks. I would think you would see visible signs on detonation on other pistons if detonation was indeed present.

            These two motors were factory crate mercury marine motors complete with carb, fuel pump, distributor, plugs, wires all installed. It might have been possible that a crossfire from a wire to wire induction may have been present but it was not at all noticeable in the performance.

            The only thing I see different on the new motors is they have a anti knock sensor on the side of the block but I have no idea how it could be checked.

            Thanks for your comments.[ATTACH]Click image for larger version

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            Last edited by markotah; June 8th, 2010, 07:45 AM. Reason: add picture

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            • #7
              Re: New Mercury 350 motor w/ hole in piston

              Originally posted by markotah View Post
              The only timing that was checked was on one using a timing light and the factory marks. I would think you would see visible signs on detonation on other pistons if detonation was indeed present.

              These two motors were factory crate mercury marine motors complete with carb, fuel pump, distributor, plugs, wires all installed. It might have been possible that a crossfire from a wire to wire induction may have been present but it was not at all noticeable in the performance.

              The only thing I see different on the new motors is they have a anti knock sensor on the side of the block but I have no idea how it could be checked.

              Thanks for your comments.[ATTACH][ATTACH]55805[/ATTACH][/ATTACH]
              No expert in hole in pistons, but this does not look like the typical detonation photos I have seen posted here before. Almost looks like the piston hit something that wasn't moving around the cyl, and punch through. I will be interested in what the experts say.

              PS: what did the plug look like from that cyl?

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              • #8
                Re: New Mercury 350 motor w/ hole in piston

                plug showed no damage

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                • #9
                  Re: New Mercury 350 motor w/ hole in piston

                  Not true. Detonation often occurs on one and only one cylinder. People want to think that everything on a multi-cylinder engine is equal when truth is it is far from it. Thats what blueprinting is for and why its expensive to have done right.
                  You meet the nicest people at the American Legion.
                  "maintenance is always cheaper than neglect"
                  "certain parts are USCG approved for a REASON"
                  "just because it's in the factory service manual, doesn't mean it's correct"

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                  • #10
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                    Re: New Mercury 350 motor w/ hole in piston

                    Originally posted by markotah View Post
                    plug showed no damage
                    How about the head chamber for that cyl?

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