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Do you adjust the spark gap on fine-wire spark plugs?

This is in regard to a 2000 Chevrolet Silverado 1500 with the 4.8L engine.

The emissions label specifies a spark plug gap of .060, which seems kind of high, although the used spark plugs of unknown age and mileage have a much bigger gap than what is specified. They are Autolite AP5245.

I decided to go with NGK G-Power spark plugs, p/n TR5GP, which are offered on Rock Auto for this vehicle. These are fine-wire platinum spark plugs. I have used NGK G-Power spark plugs in my other vehicles, without adjusting them, however the difference between the pre-set gap of .034 and the recommended setting of .060 is large enough that I have to ask.

If you have ever used this type of spark plugs, did you adjust it, or just install as it comes?

Do you have a compelling reason to not use the original type plugs?
If you’re really stuck with the NGKs I suggest you don’t mess with the gap.
If it doesn’t run right then take the chance re-gapping.
Unless you have the touch of a watchmaker I recommend you keep yer paws off the fine wire plugs.


I may be wrong but platinum I think you can, but iridium I believe are too brittle and you don’t change the gap. I think most cars now use a 60 gap but are you sure you got the right plugs?

Yeah, I’d use the exact plugs that came on it.

Mostly nowadays plugs come pregapped. I don’t know what year or make it was but I ran into an engine that had in one year two different engine specs. The first half of the year had plug gap different than the second half of year. Same plug different gap. Ever since then I’ve checked all gaps before installation.

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The plug type and gap should match the vehicle spec. The ignition system is designed for a certain gap range. You can and should re-gap any type of plug to match the specs for your vehicle. Normally, if the plug is intended for your vehicle application, the gap will be right or at least close. No way I would install a .035 gap in a .060 application…use the right tool and little risk of damage…


I disagree

Sounds pretty standard to me

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Sounds about right to me and many plugs do not come pre-gapped in spite of the tales.

The ones in my Fords call for .054 and every plug I’ve purchased over the past 20 years has been right around .045 or so. They can be adjusted. The trick is to not get ham-handed with them.

And for what it’s worth, those new plugs will do absolutely nothing for your vehicle in regard to mileage, performance, and so on. The ones called for by the factory work as well as anything; just a lot cheaper.


GM reduced the spark plug gap specification when they switched from platinum to iridium tips;

The original spec was .060", the revised gap is .040".

All of the spark plug listed for this truck in the Rock Auto catalog have a spark plug gap of .040".

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As a shop we always replace spark plugs with the same brand and spec that the car came with, or whatever spark plug has been updated to fit your engine. For example the original Delco spark plugs that came in your truck have been superseded to a new number and are now iridium instead of platinum (if my memory is correct).

Anyway, .060" gap is correct for the original plug type and I would recommend using Delco spark plugs in your GM. The .060" gap has been standard on many GM engines for over 40 years now. Believe it or not, there was one engine that specified .080 gap. Anyway, I would always look at the latest service manual to verify the proper gap.

Given the age of the truck, there’s a chance one or more of the wires may not survive spark plug replacement, they run right near the exhaust manifold. Might just want to replace those as well.


Interestingly, my gap adjustment tool only goes up to .050, so it sounds like I can adjust these plugs to that, and it should be close enough. Also, I noticed that the ignition wires are all original with a 1999 date code on them, and some of them have rust on the metal spring. So even though the truck ran fine, I guess I should buy a new set of wires. I actually brought them inside, and I was going to clean up the springs with sandcloth.

I would check with the Chevy dealer to see what plugs and gap are recommended for your engine. I have see cars or trucks that have changed the plug and/or gap after it is a few years old because of in service problems that showed up.

The spring is part of the heat shield, you reuse those when replacing the wires.

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Plugs have been pre-gaped for over 30 years. And from my experience about 20 percent are not gaped properly. Doesn’t matter the manufacturer.

You can cap plugs (even iridium), but you have to be extremely careful. You don’t shove a feeler in the gap to spread the gap. Use the tool as it was designed to be used.


I would think they originally came with AC/delco plugs. Myself I would get the AC/Delco Iridium plug for this if they have one otherwise the platinum version .All the plugs for the 4.8 look to be a .040 gap . AC/Delco double platinums are $4.73 a piece on rockauto .

GM has been using NGK plugs for a few years now in some of their vehicles (mainly trucks). I have no idea what the OEM plug manufacturer is for this truck/year. But if it is AC/Delco, then I agree - stick with AC/Delco.

Pregapped does not mean they all are gapped correctly. I’m sure it’s a mechanical process, and there is variability in that process. Having outliers means that the process isn’t completely in control. That’s a common issue, and may or may not be controllable, depending on the equipment.

As I understand it the reason not to use a feeler gauge on Pt or Ir plated plugs is the sharp edge of the blade can shave the thin plating off if the plug tip whereas a round wire is much less likely to cause damage. Even with the wire gauge, use a light touch and don’t try forcing it through.

Thank you all for your assistance with this matter. I ended up adjusting the plugs to a .050 gap. I have not run the truck in all this time due to the amount of work being done to it, and the fact that I needed to order more parts online. Once everything is put back together I will let you know how well it runs.

You can put the feeler gauge next to the gap and determine the gap.