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Discussion Starter #1
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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Some guy
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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?
 

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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
 

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just a ski boat with bark
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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.
 

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It's what we do
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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
 

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Discussion Starter #10
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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