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0x66 piston detonation

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  • #1

    0x66 piston detonation

    Hello everyone. First time post here. I recently blew the middle port side piston on my engine without any warning. The mechanic at first said it was the middle LP lift pump? I had them go bad in the past where it could not keep up with the VST tank and it would cause the motor to drop off at a high rpm. The powerhead was replaced along with a new VST filter, and mechanical oil pump on the block. Also the filter and lines were cleaned and replaced in the remote oil tank. The piston basically melted, although some of them looked to be okay. Every year I clean the O2 sensor and I replace the spark plugs.
    This year I did not change the plugs.
    I'm not convinced that the problem was resolved. Has this ever happened to anyone. Was a root cause discovered? Any info would be much appreciated.

    engine model: l250txrx
    Tags: None
  • #2
    without seeing the piston its hard to say.
    typically a blown lift pump wont detonate a piston but it can take out a crankshaft.

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    • #3
      Thanks for the reply rod bolt . I am sorry but I do not have picture of the top of the piston. Not sure if it was do to lack of oil or over fueling? There was no alarm or indication when the piston failed. That's what is puzzling to me.

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      • #4
        lack of oil or over fueling typically wont cause detonation.
        detonation is typically caused by lack of fuel.

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        • #5
          Krause Powerhead 010.JPG

          I do have a pic that I remembered having. Does this look to be caused by a lack of fuel?

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          • #6
            That certainly looks like detonation damage.

            Poor fuel quality and/or high temperatures can result in detonation. Perhaps the injector for that cylinder is partially clogged causing the mixture to be leaner than normal, resulting in that cylinder getting hot (compared to the good cylinders) and causing the detonation.

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            • #7
              OK here is the deal , you never changed the thermostat on this motors ,used low grade fuel and run a very lean oil to fuel ratio supply. if the piston melts its the temp as your thermostat is faulty causing high temperature and the fuel mixture being lean basically runs the cylinder dry causing the piston to melt . your piston wont explode but if it does it will make a big hole in the side and if kept running it would have caused your crankshaft to bend slightly ,the melting not only would have occurred in the piston but also all main bearings would have gone too

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              • #8
                Originally posted by madharchod View Post
                OK here is the deal , you never changed the thermostat on this motors ,used low grade fuel and run a very lean oil to fuel ratio supply. if the piston melts its the temp as your thermostat is faulty causing high temperature and the fuel mixture being lean basically runs the cylinder dry causing the piston to melt . your piston wont explode but if it does it will make a big hole in the side and if kept running it would have caused your crankshaft to bend slightly ,the melting not only would have occurred in the piston but also all main bearings would have gone too
                You certainly have a vivid imagination!

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                • #9
                  if it were due to an O2 sensor,T-stat or fuel in general you most likely would see some damage on other cylinders.
                  oil is mixed in the VST and the fuel/oil mix is fed to the injectors.
                  O2 sensor trims A/F mix to all 6b cylinders.
                  2 T-stats control temp on both banks.
                  if only one cylinder shows any damage then isolate things associated with 1 cylinder.

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                  • #10
                    OP statement "The piston basically melted, although some of them looked to be okay."
                    Makes you wonder how many pistons had damage and which ones

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                    • #11
                      Thanks for everyone's input. It happened so fast that I believe the damage was isolated to the one piston. Though I did not see the engine torn down. When it happened, engine loss power under cruise speed. Killed the engine restarted it with no knock and went under power again. Loss rpm immediately and stopped the engine. Engine had a knock at that point. Next I pulled and checked the plugs and noticed the electrode was bent up into the plug on the bad cylinder. Engine was running for 5-6 hours that day prior to the issue?

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                      • #12
                        So you do not know for sure if any other piston had any damage.

                        You need to find out for sure, it will help to find what caused it..

                        I would be sending off the injectors to have them tested and cleaned.
                        See what their report has to say the as found shows.
                        Make sure they are marked well as to which cylinder they came from

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                        • #13
                          i reckon we have a lot of apprentice here on this forum who like to learn and make money quick ,nice try guys experience comes at a price and takes time
                          cheers

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                          • #14
                            50:1 on the oil mix. I run Valvetech fuel with additives. Thermostats were never changed. Makes sense what you said. I'm going to check thermostats and the injectors. Thanks guys.

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