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Spark plug gap narrows during life?
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GDMFSOB
 
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Question Spark plug gap narrows during life? - March 10, 2013, 04:11 PM

Ok, call me crazy. I just replaced my spark plugs in the track whore. I always check the gap before I install plugs. Always. In looking at my old plugs they looked like the gap was less than what I put in. So for giggles, I checked them. Each one is less than what is specified. I always thought that the electrode wore away during use. What up with that?
If it matters:
'07 ZX6r
CR9EIX Iridium plugs
1.5 +/- seasons on plugs
Spends its life >11000 rpm


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March 12, 2013, 03:33 AM

Carbon build up???


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March 12, 2013, 07:07 AM

Mechanical contact (piston, valve, debris), dropping the spark plug and dinging the strap on the way in, some say detonation can do it as well.
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March 12, 2013, 10:19 AM

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Originally Posted by Leoallafila View Post
Carbon build up???
+1

Or they weren't gapped to what you thought they were when you put them in.


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March 12, 2013, 11:56 AM

You won't get much carbon build up on an iridium unit.
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March 12, 2013, 12:04 PM

I would go with piston contact over carbon build up.





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March 12, 2013, 12:10 PM

I'd agree with piston contact if it was a thumper or if only one or two sparkplugs had narrowed. Seems unlikely that all 4 ( I assume unindexed plugs) would be under spec by the same amount due to contact. But hey, stranger things have happened.


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March 12, 2013, 12:20 PM

Some have stated that detonation can do it but I would think that the compressive forces on the detonation side would work on all sides of the strap.

I have seen plenty of guys drop the plug in the hole or ding it on the way down and ask as the gap was tight.
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March 12, 2013, 01:43 PM

Just a guess, but: Occam's Razor. The simplest, easiest explanations are the most likely:

A. Bumped the electrode(s) while dropping them down the well in the head.
B. Used a different gap gauge than the first time.
C. Swilled too much beer when changing plugs the last time........hard to focus on those teeny numbers when the room is spinning.........


Irridiums are fine wire plugs, neh?

Unless it's getting SOOO HOT in the CC that you are blasting off molten parts of the piston crown that is then depositing on the center electrode, all whilst NOT eroding the side electrode (not bloody likely); well, then unless the piston crowns are making contact (did we shave the head a wee bit much or go with an ultra thin headgasket?) then any other answers other than the top three are unlikely....unless you have HUGE carbon deposits on the piston tops, which is doubtful at 11k RPM+.


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March 12, 2013, 03:47 PM

the gap knows its gonna get some rubbing so it flinches


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March 12, 2013, 03:57 PM

@ Deep!
Definitely not carbon build up. Way too hard for that. They all look like a clean burn should. I know I used the same gap tool that i always do, and the spark plug socket I use has a rubber retaining grommet. I don't drop them down the hole. Beer is a possibility, but I don't physically gap the plugs. You are not supposed to change the gap on an iridium plug, so they say. I just check before I put them in. Historically throughout my bikes they are well above the minimum gap out of the box. Typically near the max. I am (nearly) positive I would have remember if they were near the low end. Except for the beer thing.
I was afraid of piston contact, but there is no shiny spot on any of the plugs like I would expect for metal to metal contact. I guess I will go spin the crank by hand and pull them back out to see. Unfortunately, I do not know which cylinder the worst one came out of. Of course, spinning by hand is not the same as winding it out on the track. However, if a wrist pin or something is going, I would have already expected it to grenade.
I'll post up what I find in a bit.


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March 12, 2013, 04:12 PM

Quote:
Originally Posted by The Evil Twin View Post
@ Deep!
Definitely not carbon build up. Way too hard for that. They all look like a clean burn should. I know I used the same gap tool that i always do, and the spark plug socket I use has a rubber retaining grommet. I don't drop them down the hole. Beer is a possibility, but I don't physically gap the plugs. You are not supposed to change the gap on an iridium plug, so they say. I just check before I put them in. Historically throughout my bikes they are well above the minimum gap out of the box. Typically near the max. I am (nearly) positive I would have remember if they were near the low end. Except for the beer thing.
I was afraid of piston contact, but there is no shiny spot on any of the plugs like I would expect for metal to metal contact. I guess I will go spin the crank by hand and pull them back out to see. Unfortunately, I do not know which cylinder the worst one came out of. Of course, spinning by hand is not the same as winding it out on the track. However, if a wrist pin or something is going, I would have already expected it to grenade.
I'll post up what I find in a bit.

????? Huh? If they aren't in spec to begin with, than you have to reset the gap. Here's a tidbit from the Denso site:

Q. How do I gap Iridium plugs
A. Before attempting to gap any DENSO Iridium Power spark plug, please review the specification chart to see the factory-preset gap. In most cases your Iridium Power plugs do not need to be gapped. Even with small variations in the factory set gap the ultra-efficient firing power design will compensate for those small variations. Should you decide to re-gap your Iridium Power plug, use extreme caution as improper gapping may damage or destroy the Iridium center electrode or porcelain center. To increase the gap size: Step 1 Use needle nose pliers or spark plug gapping tool to bend the ground strap up to the desired height. DO NOT LET THE PLIERS OR GAPPING TOOL TOUCH THE IRIDIUM CENTER ELECTRODE OR PORCELAIN. Step 2 Re-check the gap with a calibrated gapping tool. To decrease the gap size: Step 1 Use the same method as above, however bend the ground strap down to the desired height. DO NOT LET THE PLIERS OR GAPPING TOOL TOUCH THE IRIDIUM CENTER ELECTRODE OR PORCELAIN. Step 2 Re-check the gap with a calibrated gapping tool. WARNING: Failure to follow these directions may permanently damage the spark plug. Note: Never use a round gapping tool to check the gap or to increase or decrease the gap setting.


If a wrist pin is going you would likely hear the double tap noise that comes with it. As in tune with any noise or minor thing out of whack with the bike as you are, I think this is unlikely. Wish I could come up with an explanation on this other than the aforementioned beer theory.


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March 12, 2013, 06:34 PM

Quote:
Originally Posted by Toecutter View Post
Note: Never use a round gapping tool to check the gap or to increase or decrease the gap setting.
Maybe that is what I remember reading. I dunno, never had to adjust them. Fuck, now I will be making sure they are all within .00000000324 mm


Well, I spun the crank a few times and re checked all the gaps. Each one was between .030 and .031. So, no way to account for the really narrow gap on the one, and the < .027 on the rest. No other explanation except for

Guess I will just ride it like I stole it!


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Last edited by The Evil Twin; March 12, 2013 at 06:38 PM..
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March 13, 2013, 07:25 AM

Spinning the crank by hand will not indicate the clearance issue. The stretch and resultant contact will come at super high velocities and when the motor is running really high.

My original theory of bumping the strap stands.
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March 13, 2013, 09:16 AM

Quote:
Originally Posted by BlackHatch View Post
Spinning the crank by hand will not indicate the clearance issue. The stretch and resultant contact will come at super high velocities and when the motor is running really high.

My original theory of bumping the strap stands.
Yeah, I know the inertial forces are much much higher. I guess (hope) that I just fucked up when installing. It seems to take a pretty good knock to move it though. I test dropped one of the old ones from about 10" and it closed slightly. I know the work bench top, wood, absorbed some of the force. It can also be like when you drop a bottle- sometimes it breaks and sometimes it doesn't. Just depends on how the force is applied.
I hate to do it, but looks like I will pull them again after the first event and see if anything changed dramatically.
I really really REALLY can't afford a rebuild or replacement this season Daughterkid's passion for dance is eating serious $$$ this spring, but she comes first.


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