Spark plug gap difference

[banderberg]

The spark plugs I'm using for my 3.0L have a 0.031" gap. The engine specs call for 0.035" gap. Is that tiny difference going to matter?

 

[ThomW]

You should be using the plugs that your motor recommends using. Why are you using something else? They make plug gapping tools so you can set the gap on your plugs to the correct specs. It may not cause much of an issue...but why add the chance of it causing an issue?

 

[Scott06]

The spark plugs I'm using for my 3.0L have a 0.031" gap. The engine specs call for 0.035" gap. Is that tiny difference going to matter?

No but you can gap them to .035 unless you are doing iridium plugs

 

[banderberg]

You should be using the plugs that your motor recommends using. Why are you using something else? They make plug gapping tools so you can set the gap on your plugs to the correct specs. It may not cause much of an issue...but why add the chance of it causing an issue?

The cover on the carb flame arrestor has all the information about the engine including spark plugs which it says should be "AC-MR43T". When I went to buy these, the store didn't have them and I don't recall specifically but somehow I landed on the NGK BR6FS plugs as being compatible.

 

[banderberg]

No but you can gap them to .035 unless you are doing iridium plugs

I had thought about doing iridium. Never used them before, but sounds like they can't be gapped?

 

[banderberg]

You should be using the plugs that your motor recommends using. Why are you using something else? They make plug gapping tools so you can set the gap on your plugs to the correct specs. It may not cause much of an issue...but why add the chance of it causing an issue?

This is where I found that I could use the ones I have now

spark plug cross reference

www.sparkplug-crossreference.com

 

[ThomW]

I had thought about doing iridium. Never used them before, but sounds like they can't be gapped?

They can be gapped, but you need to b extra careful as the thin wire can be damaged very easily. If you go with the Iridium, and they are gapped at .0031, I don't think the .0004 difference will affect much. Or go wit hregular plugs and set the gap to the .0035. I prefer the NGK over AC plugs anyway....

 

[Alumarine]

Those plugs at that gap will be fine.
If you haven't installed them you could gap them to .035"

 

[Scott06]

I had thought about doing iridium. Never used them before, but sounds like they can't be gapped?

correct some of the higher end plugs like iridium are pre-gapped and you cant change them. Don't waste your money on iridium for a 3.0 standard ac delcos will be fine and you can replace them five times for the same cost ...

what plug are u using or did you just not gap them and it was .031" out of the box

 

[Drcoffee]

And the myth of not gapping iridium plug continues…google is your friend. If you still believe this, go to the Denso website, one of the industries leading spark plug manufacturers.
Installing iridium plugs

no spark plug can be pre-gapped for all engines from the factory. Pre-gapped gets you close to the average gap but the plugs still need to be gapped correctly to be consistent in all cylinders. Never install plugs straight out of the box. If you are that timid then hire a mechanic.

when I did my plug and went with iridium, I emailed Denso support to verify the correct plug based on what plug came from the factory. They responded within 48 hours to confirm I had the correct plug and heat range.

most people are not old enough to recall copper plugs on carb’d engines fouling out every other outing. It sucks to have to replace standard plugs before you can run an engine, Just because they are carboned up. The iridiums work great in my 1995 5.7 Rinker

 

[Scott06]

And the myth of not gapping iridium plug continues…google is your friend. If you still believe this, go to the Denso website, one of the industries leading spark plug manufacturers.
Installing iridium plugs

the first paragraph states...

"In most cases your Iridium Power plugs do not need to be gapped"

 

[SternDriveEd]

If you are changing spark plugs you will always need to check and correct the gap on the new plugs. Otherwise you should not be attempting this service on your engine. I would compare this to filling the tires on your car without checking the tire pressure when you’re done.

 

[Drcoffee]

the first paragraph states...

"In most cases your Iridium Power plugs do not need to be gapped"

For context
“In most cases your Iridium Power plugs do not need to be gapped. Even with small variations in the factory set gap the ultra-efficient firing power design will compensate for those small variations. Should you decide to re-gap your Iridium Power plug, use extreme caution as improper gapping may damage or destroy the Iridium center electrode or porcelain center.”

LOL. In every case I have installed any spark plug, they needed gapping. I guess the key words are “in most cases”. You might get lucky that its correctly gapped. In which case I agree.

you can even gap them slightly wider with no ill effect. Since iridiums dont wear out as fast as copper you can treat them as slightly worn and still run fine. Copper plugs last only 25,000 miles vs iridium at 120,000 miles. I pulled the plugs from my toyota at 180,000 and the gap was still in spec from the factory Install. I also pulled the copper plugs from my used 4runner at 220,000 miles and the gap was twice the spec size. Iridiums dont wear out.

what you dont want is a small gap which results in a small flame kernel and poor ignition.

 

[Rick Stephens]

You can gap iridium plugs. A little care is all it takes. Not sure the value with iridium in most boats as their purpose is extended life. In my admittedly limited experience, most pleasure boats don't get enough use to justify it.

You can substitute to different compatible plugs to your hearts content. Knock yourself out. That is why there are crossover charts.

I just changed the iridium AC Delco plugs in my 8.1L chevy... after 125,000 miles. The electrode was wearing and the gaps were over .090. Prob should have changed them before 100,000.

 

[achris]

The cover on the carb flame arrestor has all the information about the engine including spark plugs which it says should be "AC-MR43T". When I went to buy these, the store didn't have them and I don't recall specifically but somehow I landed on the NGK BR6FS plugs as being compatible.

BR6FS are the NGK equivalent for the MR43T. They are a perfect replacement for the AC plug (I only use NGK spark plugs). 31 thou isn't going to cause any problems.

Are you having run issues?

Chris...

 

[banderberg]

BR6FS are the NGK equivalent for the MR43T. They are a perfect replacement for the AC plug (I only use NGK spark plugs). 31 thou isn't going to cause any problems.

Are you having run issues?

Chris...

Yes my 3.0 takes too long to start, requires me to nurse throttle for a while before it will idle without dying, and idles rough, shaking side to side. Smooths out if I increase throttle. I'm replacing the points with pertronix and the coil with a flame thrower, new cap and rotor, I installed a fuel water separator. If none of that helps I'll look at replacing or rebuilding the carb.

 

[achris]

Yes my 3.0 takes too long to start, requires me to nurse throttle for a while before it will idle without dying, and idles rough, shaking side to side. Smooths out if I increase throttle. I'm replacing the points with pertronix and the coil with a flame thrower, new cap and rotor, I installed a fuel water separator. If none of that helps I'll look at replacing or rebuilding the carb.

That sounds like a carburettor problem...

 

[Drcoffee]

Chris, would adding Techron to the fuel help the problem.

 

[achris]

Chris, would adding Techron to the fuel help the problem.

Snake oil will always help (the snake oil manufacturer's bottom line)... ie, no such thing as 'mechanic in a can'.

Chris...

 

[Rick Stephens]

Carb rebuild time.