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Spark plug - which way do they face?

Old 02-21-2005, 08:17 PM
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Default Spark plug - which way do they face?

I have read conflicting suggestions about how to face your spark plugs when installing. What I mean by this is the direction the opening is supposed to face.

Some people say that it should be to the right. Others say that it really doesn't matter. Anyone have an opinion?
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Old 02-22-2005, 05:12 AM
Join Date: Aug 2003
Location: Binghamton,NY
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that is an older race car type idea, called indexing
the opening faces the intake valve.
auto racing stores sell shims/gasket rings of different thickness sizes, so when you screw in the plug it will face in the direction you want with the correct gasket,
Does it work ???
I really have no idea, but many claim it does.
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Old 02-22-2005, 05:44 AM
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Location: Flanders, NJ
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Question Why worry about it?

I've read about this before, and if I remember correctly, they say that the electrode gap should face the intake valve. (or is it the exhaust? Hmmmm) Anyway, as far as how much of a difference this actually makes for performance, I really have my doubts. Think about it this way: During the compression stoke, both intake and exhaust valves are closed (duh), and the entire combustion chamber is full of the fuel/air mixture. Once the plug fires, it ignites the mixture in the cylinder. The "flame" in the cylinder will propagate away from the initial source of ignition. Seems to me the ideal direction that you want this to happen is straight down toward the piston. Why facing the spark plug electrode gap toward either valve is supposed to be the cat's *** is beyond me. As long as you have the proper fuel/air ratio, the plug is the of proper heat rating, and has a good strong spark, you're going to get proper combustion. Sounds like a case of people over analyzing **** to me.
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Old 02-22-2005, 06:16 AM
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In school I learned that the only time it makes a difference is if you have a piston with a crown on top. If you have a flat piston head it doesn't matter. It depends on how picky you want to get about your combustion. I wouldn't worry about it unless your racing.
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Old 02-22-2005, 10:59 AM
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Well I'm not really "worried" about it, I just know a few guy's who swear by this, and wanted to get more opinions. I have a stock setup so I really don't think its gonna do much anyway.
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Old 02-22-2005, 04:24 PM
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Accel sells a spark plug indexer kit..... comes with indexer tool and spacers/washers.......I know racers swear by this.
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Old 02-27-2005, 07:08 PM
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It really doesn't matter which way the gap faces. Flame propagation is almost finished by the time you realize it's started. Put your bike on a dyno sometime and try it. If it really worked, you'd be hearing about its advantages from all the race teams.

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Old 02-11-2006, 05:29 AM
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Default indexing

I think the reason you don`t here about it from race teams is because they all do it ,(it`s pretty much a given for them).Kind of like having new oil in the motor vs. old oil.My 2cents.Toby
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Old 03-03-2006, 12:39 AM
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I agree with junky. during combustion there both closed. the only Possibly secnario i can attempt to draw by having the spark plug face a certain way is if somehow by facing the plug twords the intake the electrode gets sprayed with the gas creating a more intense spark for faster combustion. Other than that i cannot see any possible way why it would madder. but if you think it does give it a shot, i dont think it can hurt so eather it will A. help or B. not do anything, im leaning twords b but like i said cant hurt to try
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Old 02-13-2007, 01:03 AM
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That depends on your bike type, I guess. Check with your dealer.


Bajaj USA - Download Bajaj USA Catalogs
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Old 08-04-2010, 07:03 AM
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Junk walks the steps to combustion. You will detonate no matter what indexing if you go messing with nature. She does not live in a pressure or vacuum world. I would though, invest in copper washers.
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