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Discussion Starter #1 (Edited)
I’ve read several warnings in various posts / articles not to gap NGK Iridium plugs as it will surely damage them. They are supposedly factory pre gapped and need no further attention. I have just found this not to be the case.

The recommended gap for the 2004 2.0 litre engine in my WRX is 0.7 mm – 0.8 mm (.028” - .031”). Just bought a box of four BKR6EIX plugs. Using a wire type gauge to measure, two were gapped at .030” and the other two were somewhat higher - out of the suggested range of .028” - .031”. Without having wire gauges of .031” or .032” I’d guess the two were at least that or more. An old standard I learned long ago was a plug will normally wear .001” per 10 k miles. Is this still the case? That was well before platinum or iridium came along.

I carefully gapped the last set of BKR6EIX plugs I installed nearly 40 K miles ago to .028” – the low end of the suggested range, allowing for normal wear through the life of the plugs to remain within the 0.7 mm – 0.8 mm recommendation. As memory serves, they were all at .030”. I’ll be pulling those soon and will check the gaps.

WHAT? I gapped Iridiums? Twice? FOOL! This had to have destroyed them! It obviously did not. I’ve had a lot of practice gapping plugs - 37 years’ worth.

There are supposedly modern plugs with a fine wire center electrode that cannot be gapped or they will likely be ruined. I’ve never seen one. Iridiums are not a fine wire and are not nearly that fragile from what I can see. I have a 1970’s Radio Shack 50x pocket microscope. It was sold to check the condition of your tonearm stylus to play vinyl. Using this microscope, I had a look at the iridium center electrode on all four plugs before and after my gapping them. The center electrode is tapered and tipped with a coating of iridium. The transition from the two metals is very clear color wise. The iridium is ground quite smoothly, making a near perfect right angle all the way around the electrode tip. My careful gapping efforts had zero effect on the tip of the electrode. Wish I could provide images of the iridium at 50x magnification to prove my point. Just take my word for it.

It looks as if the iridium tip could be dislodged with a really rough gapping technique. I have no idea of what is bonding the iridium on the tapered electrode. I was super careful to keep the gapping tool away from the ceramic insulator or the electrode tip as I bent the ground electrode into place.
 

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Discussion Starter #2 (Edited)
I wrote the post above yesterday in anticipation for today. I now have more info and images. Both examples in the image have the same part number of: BKR6EIX

Iridium plugs wear faster than I thought. The old plugs had 38552 miles on them. They were installed with a gap of .028". All four of the removed plugs had a .040" gap. I like consistency.

Using my trusty microscope, I can see the center electrodes were still tipped with iridium. They are no longer flat right angled smooth surfaces. They are now somewhat rounded and pitted. The ground electrode has worn away quite a bit as well.

A best as I can do image is below. On the left, it appears as though the center electrode is white in color. Under the microscope, it is actually metallic silver, rounded and pitted.

Full resolution: https://farm9.staticflickr.com/8751/17048371725_186fb4bdb9_o.jpg

 

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Wow, I am surprised at the wear. Looks like it was definitely time to change them. Very nice write up. I put my Irridium's in about 20,000 or so ago. Now I feel I should check them. I set them all at .29. I used a flat gauge, but I think I will pick up a wire gauge.

Did you notice a difference in the drive after changing them out?
 

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Nice to know you can gap iridiums. Great write up, and interesting to see how fast they wear. I just installed a set of oem too only about 1000 ago and noticed a smoother idle after I had coppers in for about 10k. Once the fuel trims relearned that is
 

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I've had iridiums in for about 30K now. I wonder if your mapping has something to do with it. Also, whether wear exists and whether it matters may be two different things. We know it certainly exists, but it may not actually matter.

Your images are terrific, BTW.

I went for iridiums because I dislike changing plugs, and had hoped to leave them in longer than platinums. I think I will still do so. If/when I get a misfire, I'll know where to look first. Otherwise, we'll see in another 40K or 50 K (so, 70K or 80K total miles) what became of my iridiums.

Great thread Sasquatch!
 

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This is a neat thread. I, too, read that you should never gap iridiums due to the frailty of the electrode, glad to see it's doable.
 

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The issue is most people that have never gapped a plug before, or have just done copper plugs, use a tool like such.
 

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Feeler gauges are where it's at.

Also, from: How Long Will My Iridium Spark Plugs Last?

"A traditional iridium plug such as a Denso IK20 or NGK ZFR6FIX-11 both have iridium center electrodes, however the ground electrodes are a traditional nickel construction. The [/quote]
Ground Electrode will wear out first. Typically we have found you can expect 50-80k miles on an iridium plug. But plug manufacturers have to temper their projections as driving conditions and motor modifications differ. Additionally, because gradual wear will "round-off" firing points over time, the concentrated firing power and voltage requirement benefits will be reduced. Therefore, NGK gives them a life expectancy of 40-50k miles and Denso assigns a recommended replacement interval of 30k miles."


At 70k my last set of plugs started to cause misfire issues due to increased gap in cyl 3, which makes sense as that cyl runs the hottest. I'm now on a 50k, or better if I'm lucky to find the time to work on my car... replacement schedule. Which from the above, seems to be about right. YMMV.
 

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Discussion Starter #11 (Edited)
The issue is most people that have never gapped a plug before, or have just done copper plugs, use a tool like such.


I never liked those, even back in the day. I've always used a wire gauge. The gauge I just used (it reads .028" on the other side)

Gauge.jpg
 
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