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    Which plugs please? ​​​​​​​

    Which plugs please?

    1983 Mercruiser 260.

    I purchased the following tune up kit:
    https://marinepartssource.com/tune-up-kit-mmd-m57tbolt

    It came with BR6FS plugs. After reading on some forums, Some techs
    say it should have BR6EFS plugs in it. Old ones were thrown out so
    I'm not sure which ones are correct.

    Advise please.


    Thank you,
    Johnny

    #2
    This is a 1983 model year boat with a newer engine using the thunderbolt 4 ignition?

    Pre Vortec cylinder heads require the short reach plug (BR6FS), the Vortec cylinder head will require the long reach plug (BR6EFS).
    The NGK’s you’ve listed cross over to AC Delco MR43T and MR43LTS.
    Welcome to the club.
    Dave
    Edmonds, WA
    "THE FIX"
    '93 2556
    Carbureted 383 Vortec-Bravo II 2.0:1 18 1/4x19 P

    The rebuild of my 2556 https://www.baylinerownersclub.org/f...76?view=thread
    Misc. projects thread
    https://www.baylinerownersclub.org/f...56-gctid789773

    Comment


      #3
      Welcome! Getting the right plug is confusing at best partly because of plug development, fuels available and generation of the engine. Your merc 260 is probably a generation one small block, ie pre vortec. Here’s a link to the NGK codes and probably the best explanation I could find https://www.lsengineers.co.uk/blog/g...ng-system.html
      As I understand the difference, the EFS has an extended tip that’s going to go further into the combustion chamber, which is fine if that’s the way the heads were designed. Here’s where I have my doubts. Given the year of your engine I’m not sure that GM had gotten to the concept of getting the spark farther into the combustion chamber yet. I’m thinking the BR6FS is going to be the proper plug for your engine. However, hopefully there will be others that will either confirm what I’m thinking or address my well known intelligence deficiency.
      P/C Pete
      Edmonds Yacht Club (Commodore 1993)
      1988 3818 "GLAUBEN”
      Hino EH700 175 Onan MDKD Genset
      MMSI 367770440

      Comment


        #4
        All good points, take heed!

        You will also want to gap the spark plugs according to your ignition system.
        With a standard ignition system, you can gap them at .032"/.035".
        If you have a high energy out put system, then you can gap them a bit greater.


        Don't forget to double check your ignition system spark advance. See what it's doing at around 3,200 RPM.
        Compare your findings to your OEM advance curve.


        When you do find the correct spark plugs, keep one of the boxes, open it up, flatten it out, and tape it into your log book.


        .
        Rick E. Gresham, Oregon
        2850 Bounty Sedan Flybridge model
        Twin 280 HP 5.7's w/ Closed Cooling
        Volvo Penta DuoProp Drives
        Kohler 4 CZ Gen Set

        Comment


          #5
          I had a 1984 260. It used the MR43T plugs. I am a retired engineer. I do not second guess other engineers, so i use whatever is innthe manual, which was the MR43T (AC delco). I had that boat 15 years and it ran great.
          Captharv 2001 2452
          "When the draft of your boat exceeds the depth of water, you are aground"

          Comment


            #6
            It appears that BiggieJ entered briefly then left the building.
            🙄
            Dave
            Edmonds, WA
            "THE FIX"
            '93 2556
            Carbureted 383 Vortec-Bravo II 2.0:1 18 1/4x19 P

            The rebuild of my 2556 https://www.baylinerownersclub.org/f...76?view=thread
            Misc. projects thread
            https://www.baylinerownersclub.org/f...56-gctid789773

            Comment


            • Nauti_Mike
              Nauti_Mike commented
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