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Johnson 115 V4 - Small hole forming on # 3 piston - Need Help

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  • Johnson 115 V4 - Small hole forming on # 3 piston - Need Help

    Hi All, this is my first time posting however i have been using this forum for years troubleshooting my Johnson lol. Ok so I have a 1993 Johnson V4 115 Model VJ115TLETS. Some history: Rebuild two years ago with oversized piston on #4 cylinder. Bypassed the VRO and the motor was and is still running great! Compression the last I checked running around 115 all round. So I was winterizing my motor and noticed a small hole (not all the way through) the number 3 piston when spraying fogging oil down the cylinder. What could have caused this? I am assuming I should replace the piston but before I do I want to make sure I address the root cause. I recently fixed a cooling leak (exhaust gasket cracked near this cylinder) so would that have caused it to overheat? should I continue to run it to see if it gets worst? Perhaps someone could suggest some troubleshooting tactics?

  • #2
    Re: Johnson 115 V4 - Small hole forming on # 3 piston - Need Help

    Can you post a picture, maybe pull the head and take a good look.

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    • #3
      Re: Johnson 115 V4 - Small hole forming on # 3 piston - Need Help

      If you have a hole forming in the top of the piston, I would look at the piston edges, they are probably eroded from detonation, which often precedes preignition (what you have).

      Stop running the engine. Replace the damaged piston and repair any scoring in the cylinders. Then check your timing. Fuel quality. Fuel delivery. Loading. Cooling.

      Is your warning system working and it if is did it every signal an overheat?

      Lots of things can cause the heat that is causing that damage. To lean a mixture. Lugging the engine. Prop too big for the application. Timing off or double firing. Erratic cooling (one cylinder is hotter than the others) Poor fuel quality (old fuel or not enough octane)

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      • #4
        Re: Johnson 115 V4 - Small hole forming on # 3 piston - Need Help

        Some of the above issues cause the one piston to run hot enough to cause that damage over time-but not actually overheat the block enough to set off an audible hot horn warning. During your autopsy to find the problem, pull the head off and check the rubber water deflectors to make sure they are in correct position around the cylinders so that water flow is unrestricted. Pull the head cover off the head to see if there is anything that is restricting water flow. I'd also pull the lower carb apart and check the jets in the side of the bowl that feed #3. Look for any visual debris or restriction in the jets-esp the main. If the #3 piston was more than .030 oversize, (.040 or more) did you increase the main jet size any?

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        • #5
          Re: Johnson 115 V4 - Small hole forming on # 3 piston - Need Help

          Thanks for the quick replies! I will post a picture in the morning to give you a sense of what I am dealing with. The overheat warning system has recently been tested and works fine. The # 3 piston is not oversized but it is possible that a lean mixture could be the cause. What is a good method to determine the condition of the carb to # 3 cylinder? Prop is 17 pitch what that motor is rated for and runs at 5500 @ WOT. It might be important to mention that at idle on the moffs the revs read around 1200 rpms. Is that alot to be running out of the water? One other question, if the timing (advance) was off would that not affect all the cylinders and not just the one that I have notice visible damage? Thanks again everyone. Like I said I paid good money to have this rebuilt the first time so I want to make sure I am covering all my bases.

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          • #6
            Re: Johnson 115 V4 - Small hole forming on # 3 piston - Need Help

            First off, are you sure the hole isn't intentional? A small, taper drilled hole is often drilled in the top/center of the piston to fixture it in a lathe during the manufacturing process. See reference picture.

            Pre-ignition and detonation usually affect only one piston, initially. Depends on many factors, including lean/rich, temperature, etc. It normally shows up first on the edges of the piston crown. Severe cases will completely destroy it.
            Attached Files
            Last edited by F_R; October 17th, 2013, 03:35 AM. Reason: picture

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            • #7
              Re: Johnson 115 V4 - Small hole forming on # 3 piston - Need Help

              I do not believe the hole is intentional because the other pistons does not show this. Have a look at the picture. It surprised me when I first saw it. Thoughts?
              Attached Files

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              • #8
                Re: Johnson 115 V4 - Small hole forming on # 3 piston - Need Help

                That engine will idle at 1200 when it's on the trailer. Pretty normal. 5500 is a solid target rpm to run that engine. The factory "normal" rpms are stated to be between 4500 and 5500. It's best to run it in the upper end of that range, so you are right where you need to be.

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                • #9
                  Re: Johnson 115 V4 - Small hole forming on # 3 piston - Need Help

                  Originally posted by grayfox44 View Post
                  I do not believe the hole is intentional because the other pistons does not show this. Have a look at the picture. It surprised me when I first saw it. Thoughts?
                  Hole looks "manufactured in there" to me. Just like FR's pic.

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                  • #10
                    Re: Johnson 115 V4 - Small hole forming on # 3 piston - Need Help

                    I am beginning to be reassured. But..... a hole in the piston like one in the picture above could it have been cause by Pre-ignition and detonation? The hole does look perfect...... Should I be concerned if this is the only piston with this hole?

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                    • #11
                      Re: Johnson 115 V4 - Small hole forming on # 3 piston - Need Help

                      Thanks for all your input everyone!! I just had it looked at by a marine mechanic. He verified that the hole was manufactured. I really appreciate the quick replies and the sound knowledge members of this forums have to offer. I look forward to seeking your input in the future.

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                      • #12
                        Re: Johnson 115 V4 - Small hole forming on # 3 piston - Need Help

                        Yeah, it is definitely manufactured. Yay

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                        • #13
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                          Re: Johnson 115 V4 - Small hole forming on # 3 piston - Need Help

                          I must agree the hole definitely looks like it was an intentional part of the piston casting/machining process. But that's something I've never seen before, and I been inside alotta crossflows. Well like they say, you learn something everyday ...
                          1981 Baja 15SS_"Nine Paged"_1977 Evinrude 140
                          1981 Glastron/Carlson C500 metric series_1983 Evinrude 140_Next project
                          1971 Glastron V153_1986 Evinrude 90_Composite rebuild then unceremoniously wrecked
                          Walk Tall And Carry A Big Bilge Pump

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