Gap the spark plugs or leave them?

[mclasser]

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?

 

[bdcardinal]

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.

 

[fenixguy]

I wouldn't mess with them myself. I always check new plugs but that's plenty close enough.

 

[The_Nuke]

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).

 

[OneEyeJack]

There's the thought that they are correct and your measurement is off .001.

 

[mightymousetech]

If they have a platinum ground electrode, they can not be regapped. And 0.043 vs 0.044? Just leave them.

 

[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.

 

[SHOZ]

I always gap mine a couple thou under. But I would not put them in without checking them.

 

[slacktide_bitog]

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

 

[dkcase]

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.

 

[Kira]

I vote for post #4600800. Very funny.

 

[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.

 

[Rick in 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.

 

[Linctex]

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.

 

[Linctex]

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".

 

[Silk]

A bigger gap needs more kv, and a bigger spark...but you need the power to jump it. Big gaps in low compression low revving rich mixture engines are ok, high compression lean burn engines need a much better ignition system.

 

[Kruse]

Originally Posted By: Linctex

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

And GM quickly learned that .080 was too wide and corrected themselves. To the OP: Have you actually taken an accurate micrometer and checked to see if your feeler gauges are accurate?

 

[Lubener]

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.

Will not make a difference.

 

[Silk]

I find it hard to understand, why, with a metric vehicle, fitted with metric sparkplugs set to a metric gap...you can't take the easy way out and do it in metric ?....?

 

[Eddie]

We are way over thinking this. Just install them as is. Ed