spark plugs for 990 heads
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spark plugs for 990 heads

  1. #1
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    Default spark plugs for 990 heads

    Having trouble finding spark plugs for the 990 head. Need a short reach plug, only thing I can find is a 13/16 head. Really does not fit. I've ground/sharpened a socket wrench but the hex head literally screws all the way in, leaving nothing to bite. And a tight fit at that. I narrowed down some indexing rings to bring it out a little. This may help.

    What I really need is some gasketed 5/8 plugs with a short thread.

    Any one?

    Jerry

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  3. #2
    Some guy obnoxious001's Avatar
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    Quote Originally Posted by billet racing View Post
    Having trouble finding spark plugs for the 990 head. Need a short reach plug, only thing I can find is a 13/16 head. Really does not fit. I've ground/sharpened a socket wrench but the hex head literally screws all the way in, leaving nothing to bite. And a tight fit at that. I narrowed down some indexing rings to bring it out a little. This may help.

    What I really need is some gasketed 5/8 plugs with a short thread.

    Any one?

    Jerry
    I just looked at a couple of 990s I have here, are you sure they are not taper seat?

  4. #3
    gn7
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    LIke Barry said, triple check that the plugs is you need is a gasket plug.
    .460 reach tapered with a 5/8th is common as dirt.



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  6. #4
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    Default 990 Plugs

    When I bought my boat it had 990 heads and autolite 26 plugs, The 24 and 25 are the same but cooler plugs. I know that these may not be the best plugs but you might be able to cross reference to the plug of your choice.

    Good Luck

  7. #5
    Senior Member Trigger's Avatar
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    I run NGK R5673-8 in my flat if it helps.

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    just a ski boat with bark Carnivalride's Avatar
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    Quote Originally Posted by bigdog View Post
    When I bought my boat it had 990 heads and autolite 26 plugs, The 24 and 25 are the same but cooler plugs. I know that these may not be the best plugs but you might be able to cross reference to the plug of your choice.

    Good Luck
    If my memory is right the short reach plug from an Autolite 24 (extended tip) would be a Autilite 144. I had to run them to clear my domes on an engine before. I wouldn't run hotter than a 145 IMO.
    Quote Originally Posted by gn7 View Post
    Carnivalride, you really need to find some other hobby. You have no talent for this boat thing

  9. #7
    just a ski boat with bark Carnivalride's Avatar
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    Quote Originally Posted by obnoxious001 View Post
    I just looked at a couple of 990s I have here, are you sure they are not taper seat?
    Mine were tapered seat as well.
    Quote Originally Posted by gn7 View Post
    Carnivalride, you really need to find some other hobby. You have no talent for this boat thing

  10. #8
    It's what we do BDMarine's Avatar
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    As already stated, .460 reach tapered seat

    some NGK #'s

    R5673- (heat range 6,7, 8, etc) non projected tip
    R5674- ( ) projected tip (I run R5674-7)
    BR6FS std Mercruiser plug non projected tip
    UR6 projected tip with "V" electrode
    http://www.performanceboats.com//signaturepics/sigpic837_1.gif
    B & D Marine Performance
    El Monte, Ca.

  11. #9
    Senior Member Hullshot's Avatar
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    Jerry for the throw together you are building AC MR43T

  12. #10
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    Default plugs

    I took a real close look, and there is the slightest taper. Compared to other heads I have, it appeareds so minimal I thought gasket plugs. 5/8 taper plugs fit fine. Not much sealing surface. But I'm going with them.

    Thanks everyone.

    Jerry

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