Spark plug observation

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  • September 8, 2021 at 9:23 pm #246393
    Samuel Phelps
    Participant

      US Member

      So the replacement plug for the D-9J is a NGK AB-6 ..
      The lengths are slightly different and with the washer on the AB-6 the plug sets slightly shorter into the motor . Probably an 1/8” or so . If you remove the washer it sets the same depth as the D-9J .
      Is this a problem ? And would it hurt to not use the washer . That would help keep it further away from the plug covers on my Speeditwin .. Sorry if this is a dumb question….

      September 8, 2021 at 10:08 pm #246395
      joecb
      Participant

        US MEMBER PAY BY CHECK

        when you say “sets shorter in the motor” , you are NOT talking about the thread into the cylinder head, correct? – I suspect that you mean the length of the plug protruding outside the cylinder head. If that is the case, there is no harm, matter of fact it is a benefit in cases where there is a metal cover over the plug and wire terminal.
        With the modern line of Champion plugs , I find that on most the insulator is longer than the old style equivalent Champion plugs. This can be a problem in motors with enclosed plugs and wires… like Evinrude Zephier’s. I use NGK BM7A in my Zephyers for that reason, much shorter plug of equal heat range.

        Joe B

        • This reply was modified 4 years, 3 months ago by joecb.
        • This reply was modified 4 years, 3 months ago by joecb.
        September 9, 2021 at 6:13 am #246400
        Samuel Phelps
        Participant

          US Member

          I am talking about how far the plug sets into the cylinder head . With the washer on the plug it doesn’t sit quite as far into the head ..
          Does the washer create a seal around the plug ?
          Might it leak compression if I remove the metal washer ..

          September 9, 2021 at 8:16 am #246404
          Buccaneer
          Participant

            US Member

            The threaded portion of the spark plug is referred by the manufactures as “Reach”.
            And the plugs will probably leak without the washer.
            As long as the heat range is correct, the shorter reach plug will probably be okay.
            I’ve noticed the same “shorter” reach plugs at times, and didn’t note
            any problems.

            Prepare to be boarded!

            September 9, 2021 at 11:13 am #246411
            Mumbles
            Participant

              The washer serves two purposes. It seals the plug and also helps to transfer heat from the plug to the head. For these reasons, it should be installed.

              September 9, 2021 at 2:04 pm #246414
              Samuel Phelps
              Participant

                US Member

                Ok , thanks guys for information!

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