[SankarAu]

Hi,
My baby has clocked over 140k kms and feels slightly rough. I've picked up a 4-pack of NGK SILZKR7B11. They are all uniformly factory gapped at 0.98mm. A google search gives me gaps between 0.9 and 1.1 in various sites.

Can anyone enlighten me on the factory recommended gap, please? It's the Trophy model (Australia) if that makes a difference.

Cheers,
S

[TerryT]

@SankarAu. The NGK site at https://www.ngk.com/ngk-9723-silzkr7b11-laser-iridium-spark-plug says the gap should be 1.1mm (.043”) so that would be my optimal target. You have measured your spark plugs as 0.98mm; let’s call that “1mm” for the sake of simplicity.

Mate, I don’t know how experienced or knowledgeable you are with [laser iridium] spark plugs or gapping tools and methods, but I’ll say that if your “1mm” is accurate that is close enough for me to install the spark plugs as is, without trying to change the gap which can be fiddle-some if a rookie and expensive if you stuff up. 

With laser iridium plugs you need to be extra cautious about not leaning on the thin centre electrode when measuring the plug gap and be extra extra cautious when changing the gap, if it’s needed. 

 I usually find that the gap set at the NGK factory is good, or good enough for my intended application but when I buy new NGK plugs I will always check the gap to make sure the plugs haven’t been mishandled or are a store return which have been ‘played with’ etc.

Accurately measuring plug gaps is not rocket science but it does require the right gapping tool and the right technique.  I suggest you google the subject and watch/listen/read from reputable sources e.g. spark plug manufacturers, workshops, mechanics etc.  I had posted several posts here about a similar subject, at How to find OEM/correct spark plugs?

I have copied a few of the more important points from those posts:  "I suggest you especially watch videos from the spark plug manufacturers like NGK, Bosch, Champion, either on their web sites or on YouTube.

"It will be mentioned ad nauseum in videos that your spark plug's centre electrode is fine wire Iridium (precious) metal...it is fragile!  Traditional non-precious spark plugs have a solid centre electrode of about 2.5mm dia whereas Iridium plugs have 0.6mm tips lasered to the centre electrode...a big difference.

"If you have to adjust the spark plug gap, avoid levering/pressing your gapping tool against the centre electrode to make the correct gap!  You will damage it and at AUD$35~$40 AUD per plug, you will cry!  If you have to close the plug gap, avoid the way shown in old videos of banging the earth strap against something hard like concrete floor...that worked once, not so much now with Iridium plugs.

"I usually try to remove and install spark plugs on a cold or cool engine, if I have the choice.

"Tool Tip: If you don't have one, may I suggest you buy a spark plug socket fitted with a magnetic insert (or, at very least, a rubber insert).  The magnetic insert grips the spark plug around its single-hex (6) sides and helps you lift the spark plug out of its deep 'well' without dropping it.   My personal preference is a single-hex (6-sided) spark plug socket rather than a double-hex (12-sided) socket.  I think the socket size is 16mm (5/8").

"One last thing, when starting the new plugs into the head, I suggest not using the ratchet with your extension bar & socket.  For more sensitivity against cross-threading, discard the ratchet and use your fingers on the extension bar to 'feel' that the plug is correctly starting the thread in the head."
 
There are different opinions about the best type of gapping tool to use.  See photos below.  I avoid using the first two types, #1 & #2 (or derivatives of) if I can.  I will use tools #3 & #4.  When I was serious about plug gapping, I used tool #5 (and others with the same concept).

  Tool #1 (Not used by me)

  Tool #2 (Not used by me)

  Tool #3 (Used by me)

  Tool #4 (Used by me)

Tool #5 (Used by me, but expensive compared to above tools)

When you get pedantic (like us elderly Virgo's do) you feel compelled to use a quality vernier to measure the wire strips on Tools #3 & #4 to ensure that their markings are accurate.

[SankarAu]

Thanks @TerryT

Great detail. I have mechanical aptitude and some theoretical knowledge but have to admit not having the experience most will have. I have a feeler gauge (pix below) which gave me the 0.98...but again have to admit, not being a Virgo , haven't checked the accuracy. I get your point though and take it onboard. Last time I changed sparks, on my Ford, I didn't change the factory preset. Worked a charm. Based on your suggestion I'll do the same this time around too. When I took the measurement the other day, I did gingerly insert the feeler gauge since I was aware of the sensitive Iridium. I'd rather not mess with it again. Every extra touch is an unnecessary one.

Cheers,
Sankar

[TerryT]

Thanks @TerryT

Great detail. I have mechanical aptitude and some theoretical knowledge but have to admit not having the experience most will have. I have a feeler gauge (pix below) which gave me the 0.98...but again have to admit, not being a Virgo , haven't checked the accuracy. I get your point though and take it onboard. Last time I changed sparks, on my Ford, I didn't change the factory preset. Worked a charm. Based on your suggestion I'll do the same this time around too. When I took the measurement the other day, I did gingerly insert the feeler gauge since I was aware of the sensitive Iridium. I'd rather not mess with it again. Every extra touch is an unnecessary one.

Cheers,
Sankar

Hi Sankar, thanks for the reply.  You sound like you know what you're doing.  Feeler gauges are okay and, if they are a quality brand and the blade used was first wiped clean/dry, they will give you an accurate or close enough measurement for this application. 

[TerryT]

Hi Sankar.  I couldn't see the photo that you posted of your feeler gauge until now, which has prompted me say.... 

I mentioned in my first post about using a quality feeler gauge.  Yours, being made in China is in itself not a bad thing IF the individual gauge blades were manufactured to correct specifications.  And many cheap feeler gauges don't hold individual blades as thick as say, "1.0mm" which means one has to combine two blades to make up "1.0mm". 

Did you have to use two feeler blades 'pressed' together to find your NGK plug gap?  If you did, you should understand that that requires more care when measuring as there is a higher risk for a false reading than using just one blade to get your "0.98mm".  It’s something to keep in mind for future spark plug gapping.

IMO (based on tech material I read years ago) a plug gap measuring tool that uses "wire" lips/tips is better than a standard feeler gauge that uses "blades".  I have included photos of some of the spark plug measuring tools I have in my toolboxes.  While these tools happen to be made in the USA, more importantly my vernier calipers confirm their +/- accuracy is more than acceptable for me.  (Photos #1~#4 included in my first post were just stock images off the Internet).

  Tool#5

Tool #6

Tools 7 & 8