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Piston help please

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  • Piston help please

    Hello, I have a 1995 sea Rayder F14 with the mercury (force) 120hp motor. I was having a hard time getting on a plane so I traced it down to loss of power and found that I had 0 compression on number 4 cylinder, after tear down I found that the number 4 cylinder piston was destroyed.
    It had a hole in the piston from what appears to me is someone put too large of a spark plug into it and when. Fired over broke the spark plug and destroyed and ate away at the piston, I bored and honed it over .020 and ordered a new piston and hope it will work the cylinder walls were not bad to my surprise. But the problem i have is when I ordered the piston and done my research (what I could find) all the pistons I found did not have the 2 holes on the side of the piston like the one I removed. They were machined holes in the side about the size of a 1$ (us currency coin) and the one I ordered does not, upon checking I don’t believe it would cause any problems because when I turn the motor by hand the holes pass over the exhaust ports and intake ports on the cylinder walls but also the piston sets back far enough for the whole piston to pass over these said holes in the cylinder walls. But that’s why I am here. Would this cause a problem? Also I have a machine shop I can put the holes in the 2 pistons nearly perfect to original.
    What do you guys recommend? Any help would be great.
    Pictures below of old and new. My piston codes are 700834800A I found one with the holes but did not come with a connecting rod.
    New piston I ordered, notice no holes no holes on either side I called and asked them Old piston I took out Holes I am talking about I didn’t have the holes displayed in mine

  • #2
    that is detonation from running severely lean. your carb needs service

    those ports were in the piston for a reason.
    Cheesehead boating the Gulf Coast of FLA 27.51° N, 82.53° W

    1988 Cruisers Rogue 2420 -VP 290 DP now powered by custom 468 - https://forums.iboats.com/forum/owner...988-rogue-2420

    Past Boats
    1970 Wooster Hellion - Merc 9.8
    2002 SeaRay 190BR - 5.0 - A1G2 - "Cheeseheads in Paradise"
    1984 Avanti 170DLI -3.0 stringer- "Ship Happens"

    What’s behind you doesn’t matter.Enzo Ferrari

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    • #3
      Where did you order the pistons ?----Part # of the replacement pistons ?-----And I do not believe these holes should pass over the exhaust ports at all.-----Intake ports yes , but not exhaust !!

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      • #4
        Thank you for your responses. So the number 4 piston was from detonation from running too lean? Wouldn’t the other pistons look the same? And I ordered the piston from LandMarine. I’m not exactly sure which holes the piston moves over, but the holes on the side of the piston does pass over some holes briefly before rings pass over them as well.

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        • #5
          Those big holes should not uncover exhaust ports , PERIOD !

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          • #6
            I don’t get what you mean, the piston moves up and down the cylinder, the holes in the side of the piston cylinder wall stays stationary.

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            • #7
              Those holes in the side of the piston should never be exposed to the exhaust ports !!-----Look at your motor block and determine which are the exhaust ports and which are the intake ports !----This should be simple.----I know how this all works.

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              • #8
                Those holes are usually for the top end bearing pin. That piston has been seriously melted by a lean condition likely caused by oil delivery failure. Your other cylinders will also be likely down on compression. Too.

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                • #9
                  Thank you for your responses, so machining the holes I tot he new piston to match the old piston that was taken out would not work?

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                  • #10
                    Or would running the new piston as it is without those holes in the side of the piston be damaging to the motor?

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                    • #11
                      Talk to the seller about this issue.----Perhaps they sent the wrong piston.----Post a picture of the INTAKE side of the old / blown piston.

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                      • #12
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                        So. Just looking at the pics again. I’m now fairly certain that your pic shows the top end bearing pin holes just almost out of picture to each side. That hole in the centre looks as if it has been caused by the failure

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