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what causes a spark plug to wear out? #4550479
10/21/17 07:19 PM
10/21/17 07:19 PM
Joined: Nov 2009
Posts: 5,123
Houston, Texas
motor_oil_madman Offline OP
motor_oil_madman  Offline OP
Joined: Nov 2009
Posts: 5,123
Houston, Texas
My trimmer started misfiring at idle yesterday and almost got to the point where you couldn't let off the throttle. I put a new plug in it today and it runs like new again. I really didn't see anything wrong with the plug. Usually if it does what I described it's because a piece of carbon is causing it to ground out, but this wasn't the case. Another time on a piece of equipment I was having trouble getting it to restart when hot and that's what happened. Also the electrode had worn down to the point where that little v groove was worn and the gap was probably .050 instead of .030"


2007.5 dodge cummins 6.7 liter. Chevron Delo400 15w40. 7000 mile or 250-300hr intervals.

Re: what causes a spark plug to wear out? [Re: motor_oil_madman] #4550481
10/21/17 07:21 PM
10/21/17 07:21 PM
Joined: Jun 2003
Posts: 17,809
Deplorable in apple valley, ca
Chris142 Online content
Chris142  Online Content
Joined: Jun 2003
Posts: 17,809
Deplorable in apple valley, ca
Every time it sparks it loses a tiny amound of metal from the electrodes. Figure it sparks 8000 times or more a minute.


02 Wrangler carlube 5w30
87 F250 traveler 15w40
07 fjcruiser Chevron 10w30
Z400 castrol T 10w40
Can am maveric edge 5w40
57 case tractor 15w40
Re: what causes a spark plug to wear out? [Re: motor_oil_madman] #4550488
10/21/17 07:29 PM
10/21/17 07:29 PM
Joined: Jan 2007
Posts: 17,501
Clovis, CA
Merkava_4 Offline
Merkava_4  Offline
Joined: Jan 2007
Posts: 17,501
Clovis, CA
It's the erosion of the electrodes. Center electrode and ground electrode.

I pull mine out every so often to clean them and re-gap them.

Re: what causes a spark plug to wear out? [Re: motor_oil_madman] #4550537
10/21/17 08:01 PM
10/21/17 08:01 PM
Joined: Mar 2017
Posts: 134
northwest pa
justintendo Offline
justintendo  Offline
Joined: Mar 2017
Posts: 134
northwest pa
many times that center electrode has a crack in it, and the crack can expand/contract with temp too.
almost always a spark plug issue on a two stroke is jetting, unless theres TONS of runtime on it. if thats the case smile and toss a new ngk in there and enjoy the cheap easy maintenance of a smoker.
my dirtbikes often go several years on a plug, which can be 60 or more hours of runtime easy.


2013 escape 2.0 awd mobil 1 10w30ep
2008 fusion 2.3 mtx redline 0w20
1996 f150 4.9 2wd mtx mobil 1 10w30hm
1999 kaw zrx 1100 redline 10w40
many husqvarnas
Re: what causes a spark plug to wear out? [Re: motor_oil_madman] #4550575
10/21/17 08:33 PM
10/21/17 08:33 PM
Joined: Aug 2008
Posts: 21,194
ON, Canada eh?
StevieC Offline
StevieC  Offline
Joined: Aug 2008
Posts: 21,194
ON, Canada eh?
Also Manganese in the gas will contribute to electrode wear on the spark plug. There is a lot of this in our fuel up here at certain times of the year and it will eat the electrodes good on non-iridium electrodes.

Last edited by StevieC; 10/21/17 08:34 PM.

'18 Dodge Grand Caravan GT - AMSOIL SS 5w20
'06 Santa Fe - 535,000km AMSOIL SS 0w30 / ATF
Re: what causes a spark plug to wear out? [Re: motor_oil_madman] #4550634
10/21/17 10:38 PM
10/21/17 10:38 PM
Joined: Jun 2002
Posts: 19,484
Iowegia - USA
MolaKule Offline
MolaKule  Offline
Joined: Jun 2002
Posts: 19,484
Iowegia - USA
https://bobistheoilguy.com/forums/ubbthreads.php/topics/3090959/Physic_of_the_Gap_%E2%80%93_Spark_Plug#Post3090959

Your magneto system only has so much high voltage available to cause a spark across a specific gap and the fuel.

https://bobistheoilguy.com/forums/ubbthreads.php/topics/3092014/Physic_of_the_Gap_%E2%80%93_Spark_Plug#Post3092014

Last edited by MolaKule; 10/21/17 10:42 PM.

"Molon Labe" (Greek, King Leonidas to the Persians regarding their weapons "Come and Take Them!").
Re: what causes a spark plug to wear out? [Re: motor_oil_madman] #4550698
10/22/17 02:57 AM
10/22/17 02:57 AM
Joined: Jun 2002
Posts: 2,753
Southeastern USA
FowVay Offline
FowVay  Offline
Joined: Jun 2002
Posts: 2,753
Southeastern USA
If you've ever opened one of these things up you can see how simple they are and how failure can happen. There's much more to spark plug wear than just tip erosion. This center electrode carries the voltage to the tip where it jumps across the air gap to ground. These things run hot, are shaken like a James Bond martini, and usually run for years without so much as a hiccup. For OPE it's a wise idea to replace these simple items every few years regardless of tip wear. These pictures are of a Champion RCJ6Y that was only a year old. The center carbon conductor has failed and the plug is now used as a training aid. The poor guy that owns the blower spent his entire weekend fooling with the carburetor on this thing and he never checked his spark.


Re: what causes a spark plug to wear out? [Re: motor_oil_madman] #4550790
10/22/17 07:21 AM
10/22/17 07:21 AM
Joined: Feb 2014
Posts: 595
Margate England
Claud Offline
Claud  Offline
Joined: Feb 2014
Posts: 595
Margate England
Spark plugs in modern engines last for an amazingly long time considering the environment they have to live in. In the days of leaded gas the build up of lead oxide on the ceramic insulator meant that mostly they wouldn't survive much over 15-20k miles. 12.000 mile change intervals were the norm on most cars back in the day.
Detonation, bad fuel, oil contamination, or water contamination are all things that can shorten a plug's life. Mostly a change interval of 50-100k miles is quite normal, but it wouldn't be the case if many other factors hadn't advanced along with plug technology, particularly engines consistently kept in near perfect tune thanks to computer controlled fuel injection and ignition timing.

Claud.

Re: what causes a spark plug to wear out? [Re: motor_oil_madman] #4550951
10/22/17 10:11 AM
10/22/17 10:11 AM
Joined: Jun 2002
Posts: 2,753
Southeastern USA
FowVay Offline
FowVay  Offline
Joined: Jun 2002
Posts: 2,753
Southeastern USA
I believe the standard industry service life is 30,000 miles for regular plugs, 60,000 for platinum tipped plugs and 100,000+ for the iridium type.

I have seen completely eroded tips at 30,000 miles and I've changed iridium OEM plugs at 150,000 that looked fine. My personal recommendation to people is to use what it came from the factory with and change them when it is recommended.

Re: what causes a spark plug to wear out? [Re: motor_oil_madman] #4551030
10/22/17 12:06 PM
10/22/17 12:06 PM
Joined: Apr 2009
Posts: 2,933
Canada
boraticus Offline
boraticus  Offline
Joined: Apr 2009
Posts: 2,933
Canada
Generally speaking, spark plugs seldom fail and when they do, there's usually no physical evidence to explain why. Any plugs that I've had fail looked perfectly fine. The last one to do so was early this year in on of my ATVs. It was an NKG plug with fewer than 3000 miles on it and it looked virtually brand new. Nonetheless, it failed.

Spark plugs can be tricky. I've had two of them spark outside the cylinder but would not fire inside. That, it very frustrating. I chased that problem for over an hour before trying a different plug. Since then, I always keep a known working spark plug on hand.

Re: what causes a spark plug to wear out? [Re: motor_oil_madman] #4551124
10/22/17 02:08 PM
10/22/17 02:08 PM
Joined: Feb 2003
Posts: 7,674
Jupiter, Florida
Cujet Offline
Cujet  Offline
Joined: Feb 2003
Posts: 7,674
Jupiter, Florida
It's not unusual for two stroke spark plugs to develop a very thin conductive coating on the insulator. Leading to erratic operation or worse. Plugs are cheap, I simply throw them out.


People who count on their fingers should maintain a discreet silence.
Re: what causes a spark plug to wear out? [Re: FowVay] #4551164
10/22/17 03:04 PM
10/22/17 03:04 PM
Joined: Jan 2007
Posts: 17,501
Clovis, CA
Merkava_4 Offline
Merkava_4  Offline
Joined: Jan 2007
Posts: 17,501
Clovis, CA
Fantastic FowVay! I never knew there was a carbon center conductor. Is that other piece a spring ?

Re: what causes a spark plug to wear out? [Re: motor_oil_madman] #4551166
10/22/17 03:11 PM
10/22/17 03:11 PM
Joined: May 2010
Posts: 9,459
out there
spasm3 Online content
spasm3  Online Content
Joined: May 2010
Posts: 9,459
out there
Two strokes fire every rotation. I replace my ope 4 stroke plugs at 100hrs, 50hrs for 2 stroke.


13 elantra 72k 5w30 QSUD
03 chevy avalanche 80k synpwr 5w30
17 mazda cx-5 7300 miles m1 0w30
Re: what causes a spark plug to wear out? [Re: spasm3] #4551337
10/22/17 06:08 PM
10/22/17 06:08 PM
Joined: Jun 2003
Posts: 10,534
Illinois
javacontour Offline
javacontour  Offline
Joined: Jun 2003
Posts: 10,534
Illinois
Originally Posted By: spasm3
Two strokes fire every rotation. I replace my ope 4 stroke plugs at 100hrs, 50hrs for 2 stroke.


Many 4 strokes do too. It's not like small engines have a distributor that runs off a cam shaft. They have a magneto ignition that runs off the flywheel. The flywheel is driven by the crank, so it fires every time around, IIRC.

Many cars did something similar with a waste spark ignition. Each coil fired a pair of plugs. One on plug was in the compression stroke, the other in the exhaust stroke (360 degrees apart.) So the plug fired on every revolution in such systems.


network down, IP packets delivered via UPS -BOFH
Re: what causes a spark plug to wear out? [Re: javacontour] #4551346
10/22/17 06:24 PM
10/22/17 06:24 PM
Joined: May 2010
Posts: 9,459
out there
spasm3 Online content
spasm3  Online Content
Joined: May 2010
Posts: 9,459
out there
Originally Posted By: javacontour

Many cars did something similar with a waste spark ignition. Each coil fired a pair of plugs. One on plug was in the compression stroke, the other in the exhaust stroke (360 degrees apart.) So the plug fired on every revolution in such systems.


Right you are! My olds is waste spark, copper plugs every 25k or double platinum every 50k.

Last edited by spasm3; 10/22/17 06:26 PM.

13 elantra 72k 5w30 QSUD
03 chevy avalanche 80k synpwr 5w30
17 mazda cx-5 7300 miles m1 0w30

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