understanding surface gap plugs

[greasemonkeyozi]

Someone confirm me on this, I'm still learning about differences in boat motors and cars. <br /> Surface gap plugs are plugs that dont require gap, they are the ones with flat ends with a circle in the middle, what most boat moters run on, right? <br /> The only consern in these type plugs are differences in heat range, right?<br /> Why do outboard motors require these type plugs?<br /> What outboard motors actually use regular plugs that require gap?<br /> How do these surface gap plugs spark?<br /> Just wondering.

 

[Reel Appeal]

Re: understanding surface gap plugs

http://www.edelbrock.com/automotive/sparkplugs.html <br /><br />Most outboards use the (regular)electrode type plugs.Mercury uses surface gap plugs to meet their performance demands and combustion temp.specs.Surface gap(also called V-gap,perma-gap)plugs spark from the center outward to the outer face of the plug.The spark can jump 360 degree's around the face in the direction of least resistance. <br />Click on this link and scroll down the page a bit...

 

[Merc90HPnewbie]

Re: understanding surface gap plugs

I always kind of thought that not having the top electrode allowed the piston to move further giving a tiny increase in cylinder volume...<br />And yes with the electrodes flat like that the spark can jump anywhere within 360 degrees although I'd bet in testing you'd see that after a spark jumps one spot, there's a little carbon trace that lowers the resistance slightly in that spot, which makes the next spark jump in the same spot, which leaves slightly more carbon and so on and so on.

 

[greasemonkeyozi]

Re: understanding surface gap plugs

So with surface gap plugs,would it would be necessary to remove and clean the electrodes, or tips, more often than regular gapped plugs?<br /> Also, if they jump to 369 degreese, how much hotter is that compaired to regular gap plugs?<br /> That must be the compairison in selecting the right plugs with the right "heat range" when buying new plugs specified for a motor.<br /> Confirmed?

 

[jim dozier]

Re: understanding surface gap plugs

Merc90's description of 360 degrees refers to the direction of the spark (360 degree circle) not the temperature of the spark plug.

 

[greasemonkeyozi]

Re: understanding surface gap plugs

oh

 

[Merc90HPnewbie]

Re: understanding surface gap plugs

Doh yeah I meant it could jump across anywhere on the circle. I dont know the heat range and in fact that's something I've never really understood beyond just buying the same plug as I pulled out of the motor to replace it.<br />Fortunately I saw a picture of the plug in the service manual before I took them out of the motor. I had never seen a flat plug before and I probably would have freaked out looking for the 'broken off piece' in the cylinder....

 

[jim dozier]

Re: understanding surface gap plugs

On regular spark plugs the heat range is determined by the length of the insulator. I don't know how the heat range is determined on a surface gap plug.

 

[greasemonkeyozi]

Re: understanding surface gap plugs

I have noticed that some boat and boat motor accessories can be sold at wall mart. They have surface gap plugs on that isle, but only one kind. Would that be a type of universal plug to use on almost any motor?

 

[Merc90HPnewbie]

Re: understanding surface gap plugs

I would look the plug up in a cross reference book. There should be numbers on the porcelain or stamped into the metal part above the threads. Just like a regular plug. My boat came with champions in it, a boat mechanic told me he doesnt like champions and I should go find the NGK cross to what I had. I guess its just one of those brand loyalty things...

 

[shelbydriver]

Re: understanding surface gap plugs

I wanna know how to find the next higher heat range from my ru48 suface gap plug ngk? mine could use a little hotter plug i think