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#4600774 - 12/11/17 02:34 PM Gap the spark plugs or leave them?
mclasser Offline


Registered: 04/13/13
Posts: 2167
Loc: 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?


Edited by mclasser (12/11/17 02:35 PM)
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#4600778 - 12/11/17 02:37 PM Re: Gap the spark plugs or leave them? [Re: mclasser]
bdcardinal Online   content


Registered: 06/03/05
Posts: 10806
Loc: 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.
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#4600787 - 12/11/17 02:49 PM Re: Gap the spark plugs or leave them? [Re: mclasser]
fenixguy Offline


Registered: 02/08/17
Posts: 306
Loc: NC
I wouldn't mess with them myself. I always check new plugs but that's plenty close enough.
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#4600790 - 12/11/17 02:52 PM Re: Gap the spark plugs or leave them? [Re: mclasser]
The_Nuke Offline


Registered: 07/21/13
Posts: 252
Loc: 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).
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#4600791 - 12/11/17 02:53 PM Re: Gap the spark plugs or leave them? [Re: mclasser]
OneEyeJack Offline


Registered: 09/14/10
Posts: 7396
Loc: S California
There's the thought that they are correct and your measurement is off .001. smile

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#4600799 - 12/11/17 02:59 PM Re: Gap the spark plugs or leave them? [Re: mclasser]
mightymousetech Offline


Registered: 04/03/17
Posts: 1314
Loc: Ontario, Canada
If they have a platinum ground electrode, they can not be regapped.

And 0.043 vs 0.044? Just leave them.


Edited by mightymousetech (12/11/17 03:00 PM)
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#4600800 - 12/11/17 03:00 PM Re: Gap the spark plugs or leave them? [Re: mclasser]
Silk Online   content


Registered: 07/26/03
Posts: 4367
Loc: 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.
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#4600810 - 12/11/17 03:09 PM Re: Gap the spark plugs or leave them? [Re: mclasser]
SHOZ Offline


Registered: 06/28/03
Posts: 5603
Loc: Illinois
I always gap mine a couple thou under. But I would not put them in without checking them.
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#4600855 - 12/11/17 04:30 PM Re: Gap the spark plugs or leave them? [Re: Silk]
slacktide_bitog Online   content


Registered: 03/20/08
Posts: 5824
Loc: 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

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#4600903 - 12/11/17 05:30 PM Re: Gap the spark plugs or leave them? [Re: slacktide_bitog]
dkcase Offline


Registered: 10/20/02
Posts: 735
Loc: 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.

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#4600950 - 12/11/17 06:31 PM Re: Gap the spark plugs or leave them? [Re: dkcase]
Kira Offline


Registered: 08/19/10
Posts: 4882
Loc: Champlain/Hudson Valley
I vote for post #4600800. Very funny.

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#4600960 - 12/11/17 06:51 PM Re: Gap the spark plugs or leave them? [Re: mclasser]
Merkava_4 Offline


Registered: 01/30/07
Posts: 17501
Loc: 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.

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#4600986 - 12/11/17 07:16 PM Re: Gap the spark plugs or leave them? [Re: Kira]
Rick in PA Offline


Registered: 01/04/03
Posts: 3195
Loc: 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.
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#4601029 - 12/11/17 08:13 PM Re: Gap the spark plugs or leave them? [Re: mclasser]
Linctex Online   content


Registered: 12/31/16
Posts: 5652
Loc: 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.
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#4601035 - 12/11/17 08:17 PM Re: Gap the spark plugs or leave them? [Re: Merkava_4]
Linctex Online   content


Registered: 12/31/16
Posts: 5652
Loc: 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".
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