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Gap setting for plugs on a 3.7 470 Merc

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  • Gap setting for plugs on a 3.7 470 Merc

    I need to confirm plug gap setting on my 470. Its an 84 Mercruiser. The Manual spec I have shows 25 to 30 on the plugs and 17 on the points.
    When I pulled the plugs that were in the boat the plug gap was in the 35 to 40 range.
    I am figuring the manual spec would be correct but wondering if there would be a reason to over gap.
    THanks

  • #2
    Re: Gap setting for plugs on a 3.7 470 Merc

    Not sure what manual you are getting your specs from, but they are't what's in a Mercruiser manual and way off from the specs.
    The 470 should have a plug gap of .035"
    Points should be gapped at .022" then checked with a Dwell Meter and readjusted to 28° to 32°. Then the timing has to be reset to 8° BTDC @ idle rpm of 650 to 700 rpm
    Don S.


    Please, no PM's (Private Messages) regarding boat/engine problems.
    That is what the forums are for.
    Only forum/moderator issues will be answered in PM's.

    Comment


    • #3
      Re: Gap setting for plugs on a 3.7 470 Merc

      Thanks Don, The manual spec I got was from the Marina yesterday where I got the parts for a full tune up. He looked it up while I was there. So much for that.
      The reason I wanted to confirm is because the plugs I took out had a much larger gap and got me wondering
      . I guess I will stick with parts only from the guy I spoke with yesterday.
      Is there a technical manual I can get for the Mercruiser model motor? Motor S/N 6890496
      Most of the ones I have seen on line are for the 3.0 not much on a 3.7

      Thanks

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      • #4
        Re: Gap setting for plugs on a 3.7 470 Merc

        You need service manual number 3 for your engine, it's part number 90-95693.

        Your local Merc dealer can order you one, or you can order one directly from Mercruiser.

        https://appcenter.mercurymarine.com/...rm.jsp?type=mc

        If you order from this link, add a 0 to the front of your serial number.

        No manuals online for your engine that I am aware of.

        Many have found them on ebay.
        Don S.


        Please, no PM's (Private Messages) regarding boat/engine problems.
        That is what the forums are for.
        Only forum/moderator issues will be answered in PM's.

        Comment


        • #5
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          Re: Gap setting for plugs on a 3.7 470 Merc

          thanks Don I will get one ordered

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