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Gap the spark plugs or leave them? #4600774
12/11/17 03:34 PM
12/11/17 03:34 PM
Joined: Apr 2013
Posts: 2,559
The Northeast
mclasser Offline OP
mclasser  Offline OP

Joined: Apr 2013
Posts: 2,559
The Northeast
I've got OEM NGK plugs on the way for my Infiniti. FSM calls for a 0.043 in gap, but they come pre-gapped @.044 in. A lot of people say not to mess with the gap and just drop 'em in.

Since gaps open up over time I think I should set them to spec from the get-go. What do you guys think?

Last edited by mclasser; 12/11/17 03:35 PM.

2018 Hyundai Elantra VE
2013 Honda Pilot EX-L 4WD
2002 Honda Accord EX-L

Re: Gap the spark plugs or leave them? [Re: mclasser] #4600778
12/11/17 03:37 PM
12/11/17 03:37 PM
Joined: Jun 2005
Posts: 11,962
Santa Barbara, CA
bdcardinal Offline
bdcardinal  Offline

Joined: Jun 2005
Posts: 11,962
Santa Barbara, CA
Put them in as is. Would not lose sleep over .001" difference. You aren't building a race engine where you modify the electrode shape and index the plugs.


2014 Ford Mustang GT Track Pack
1995 Ford Mustang GT

Ford/Mazda Parts Counter
NRA Benefactor Member
Opinions expressed are my own.
Re: Gap the spark plugs or leave them? [Re: mclasser] #4600787
12/11/17 03:49 PM
12/11/17 03:49 PM
Joined: Feb 2017
Posts: 318
NC
fenixguy Offline
fenixguy  Offline

Joined: Feb 2017
Posts: 318
NC
I wouldn't mess with them myself. I always check new plugs but that's plenty close enough.


'16 Frontier SV 4x4-PP/Nissan OEM
'08 CR-V EX AWD-Valvoline Syn MaxLife/Fram TG
'01 Civic EX-Valvoline Syn MaxLife/Fram UG
'00 Civic LX-PYB/Fram UG
Re: Gap the spark plugs or leave them? [Re: mclasser] #4600790
12/11/17 03:52 PM
12/11/17 03:52 PM
Joined: Jul 2013
Posts: 455
D/FW Metroplex
The_Nuke Offline
The_Nuke  Offline

Joined: Jul 2013
Posts: 455
D/FW Metroplex
Verify they are within the range of acceptable gap for your application (into which 0.044" does indeed fall) before you stab 'em.

I've had plugs come pre-gapped at a different gap than what was listed in the book, so checking for that first and adjusting if found is more important than trying to close the gap 0.001" IMHO (something which would be very difficult to accomplish with any degree of accuracy I would think).


2012 Charger Pursuit aka "The Bacon Hauler"
- 5.7L + NAG1 (A5) + 2.62 (215mm)
Re: Gap the spark plugs or leave them? [Re: mclasser] #4600791
12/11/17 03:53 PM
12/11/17 03:53 PM
Joined: Sep 2010
Posts: 7,485
S California
OneEyeJack Offline
OneEyeJack  Offline

Joined: Sep 2010
Posts: 7,485
S California
There's the thought that they are correct and your measurement is off .001. smile

Re: Gap the spark plugs or leave them? [Re: mclasser] #4600799
12/11/17 03:59 PM
12/11/17 03:59 PM
Joined: Apr 2017
Posts: 1,522
Ontario, Canada
mightymousetech Offline
mightymousetech  Offline

Joined: Apr 2017
Posts: 1,522
Ontario, Canada
If they have a platinum ground electrode, they can not be regapped.

And 0.043 vs 0.044? Just leave them.

Last edited by mightymousetech; 12/11/17 04:00 PM.

Mighty Mouse Tech
BMW Tech, Former Acura Tech
2010 Civic Si Castrol 0W40, Redline MTL
2013 BMW 135i M Sport Edition Castrol 0W40, Redline MTL
Re: Gap the spark plugs or leave them? [Re: mclasser] #4600800
12/11/17 04:00 PM
12/11/17 04:00 PM
Joined: Jul 2003
Posts: 5,080
New Zealand
Silk Offline
Silk  Offline

Joined: Jul 2003
Posts: 5,080
New Zealand
It's a Japanese vehicle, the gap is 1.1mm, which is 0.0433070088'' Get it right - .043 is too tight, .044 too wide, set it to 1.1mm.


1987 BMW R65 - Aegis SAE30
2005 Nissan Expert - 5W-40 Castrol Magnatec diesel.
1996 Volvo T5 - Penrite HPR15 - 15W-60. Ryco syntec filter.
Re: Gap the spark plugs or leave them? [Re: mclasser] #4600810
12/11/17 04:09 PM
12/11/17 04:09 PM
Joined: Jun 2003
Posts: 5,979
Illinois
SHOZ Offline
SHOZ  Offline

Joined: Jun 2003
Posts: 5,979
Illinois
I always gap mine a couple thou under. But I would not put them in without checking them.


2008 Hyundai Accent 1.6L 5 sp manual hatchback
2010 Hyundai Genesis Coupe Track 2L Turbo 6sp manual
Re: Gap the spark plugs or leave them? [Re: Silk] #4600855
12/11/17 05:30 PM
12/11/17 05:30 PM
Joined: Mar 2008
Posts: 7,920
USA
slacktide_bitog Offline
slacktide_bitog  Offline

Joined: Mar 2008
Posts: 7,920
USA
For the I35, I would strongly suggest iridium, sine they are impossible to replace in your car since you have to remove the intake to access them. You may also want to replace the valve cover gasket, the rear 3 fuel injectors, clean the EGR tube, and possibly replace the knock sensor, too.

Platinum is good for 60k. Iridium is good for 100k

Denso #3417 or #4703

Originally Posted By: Silk
It's a Japanese vehicle, the gap is 1.1mm, which is 0.0433070088'' Get it right - .043 is too tight, .044 too wide, set it to 1.1mm.


+1

Re: Gap the spark plugs or leave them? [Re: slacktide_bitog] #4600903
12/11/17 06:30 PM
12/11/17 06:30 PM
Joined: Oct 2002
Posts: 735
Suburban St. Louis
dkcase Offline
dkcase  Offline

Joined: Oct 2002
Posts: 735
Suburban St. Louis
If indeed the original spec is 1.1mm (accurate only to the tenths place), you might think that could be rounded from 1.051 to 1.149. In which case correct could be 0.041 to 0.045. I'd say leave them.

Re: Gap the spark plugs or leave them? [Re: dkcase] #4600950
12/11/17 07:31 PM
12/11/17 07:31 PM
Joined: Aug 2010
Posts: 6,231
Champlain/Hudson Valley
Kira Offline
Kira  Offline

Joined: Aug 2010
Posts: 6,231
Champlain/Hudson Valley
I vote for post #4600800. Very funny.

Re: Gap the spark plugs or leave them? [Re: mclasser] #4600960
12/11/17 07:51 PM
12/11/17 07:51 PM
Joined: Jan 2007
Posts: 17,501
Clovis, CA
Merkava_4 Offline
Merkava_4  Offline

Joined: Jan 2007
Posts: 17,501
Clovis, CA
I would gap them! If you leave them at .044" when the manufacturer specifies .043" - you're losing .001" allowable electrode wear. That's a huge amount of wear for spark plugs that you would be just giving away.

Re: Gap the spark plugs or leave them? [Re: Kira] #4600986
12/11/17 08:16 PM
12/11/17 08:16 PM
Joined: Jan 2003
Posts: 3,203
Southeastern, PA
Rick in PA Offline
Rick in PA  Offline

Joined: Jan 2003
Posts: 3,203
Southeastern, PA
Originally Posted By: Kira
I vote for post #4600800. Very funny.


Slow night here. It turns out the last significant digit is less that the diameter of an atom.


A wise man told me:
"Heat is your friend." and "Any oil is better than no oil."
Re: Gap the spark plugs or leave them? [Re: mclasser] #4601029
12/11/17 09:13 PM
12/11/17 09:13 PM
Joined: Dec 2016
Posts: 8,027
Waco, TX
Linctex Offline
Linctex  Offline

Joined: Dec 2016
Posts: 8,027
Waco, TX
A big gap is my friend - - always has been.

Olds Big Blocks in the 70's were gapped at .080" !!!!

I usually open everything up to at least .050-.055", sometimes .060" before installing them.


"The evidence demands a verdict".
(Re:VOA)"it's nearly impossible to actually know the particular additives that are in there at what concentrations."
Re: Gap the spark plugs or leave them? [Re: Merkava_4] #4601035
12/11/17 09:17 PM
12/11/17 09:17 PM
Joined: Dec 2016
Posts: 8,027
Waco, TX
Linctex Offline
Linctex  Offline

Joined: Dec 2016
Posts: 8,027
Waco, TX
Originally Posted By: Merkava_4
I would gap them! If you leave them at .044" when the manufacturer specifies .043" - you're losing .001" allowable electrode wear. That's a huge amount of wear for spark plugs that you would be just giving away.


No, it isn't.

Sparks jump from sharp edges - the distance (gap) is NOT as important as having a sharp point/edges.
That is why iridium plugs have such a tiny wire in the center.

I have seen it on the dyno - old, worn plugs with rounded electrodes gapped down to .040" will always make less power than new electrodes with sharp edges gapped to .060".


"The evidence demands a verdict".
(Re:VOA)"it's nearly impossible to actually know the particular additives that are in there at what concentrations."
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