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Deeply recessed plugs on 55 Champion engine. Is this right?

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  • Ignition: Deeply recessed plugs on 55 Champion engine. Is this right?

    We're reassembling my 55 Champion engine today, and the machinists and I were all perplexed by the spark plugs. The factory plugs have a 3/8 inch reach, yet the plug holes in the head are almost 3/4 inch deep, leaving the business end of the plug deeply recessed in the head. The spark seems to be awfully remote from the combustion chamber. While I can attest that my engine ran well with these plugs, everyone at the machine shop agreed that having plugs recessed that deeply is odd, compared with nearly every other engine we've seen.

    A part of me wants to find a plug with a longer reach, so that the spark is actually, you know, in the combustion chamber, instead of 3/8 inch up inside a hole.

    Can someone talk me off this cliff, please?

  • #2
    What brand and what number were the plugs that were removed from the engine ?
    Factory ?
    The Shop manual calls for 6--- Champion J-7 plugs.
    Per the Championsparkplug.com site the J-7 is no longer available.
    Cross reference to a modern plug is
    Champion, Stock # 871, Part # RJ8C
    South Lompoc Studebaker

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    • #3
      That long plug just put the spark further into the chamber...not a big deal.
      I'm surprised that the pistons didn't contact the plugs....!

      But yes, normally the "spark" should be right against the chamber roof for the best flame propagation and overall performance.

      Mike

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      • #4
        Too long a plug can also cause pre-detonation problems. Without the mass of the head to pull heat away the end of the plug could get hot enough to ignite the mixture during the compression stroke. On a low-compression L-head engine this is probably not much of a problem.

        Nathan
        _______________
        http://stude.vonadatech.com
        https://jeepster.vonadatech.com

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        • #5

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          • #6
            Well, I sure thought the car ran fine before it threw a rod and got rebuilt, so maybe I shouldn't stress out over the plugs sitting up inside a recess. I'm hoping to spend some time tomorrow picking up the new engine and installing it.

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