Pre-gapped spark plugs

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I'm sure this has already been addressed but just want some clarification. I have replaced many plugs in my 36 years of life - I remember the good old days when I would adjust the gap with the precision of a NASA engineer (with a $2 tool)

Now it seems all of the plugs come pre-gapped - but I of course check them before installing. Usually I find that they are not within what the engine manufacturer specifies. Until now I always have adjusted them even though the counter guys at the parts store said not to. What do ya'll do?
 
It depends on the spark plug. For Bosch fancy crab spark plugs that can't be gapped I don't do anything. Fortunately I don't buy those plugs because I don't own a VW/Audi.

For any brand copper plug I will check gap. And on double platinum/single platinum/iridium I will visually check gap to see if the box has been dropped. If they look good, they go in.
 
I check and adjust, always have always will. I just did a tune up and 4 or 6 plugs had to be tweaked. Those boxes can be dropped and hit the floor and require the plug being gapped again. Considering how hard some plugs are to install I think not checking them is a mistake. Most of the parts counter guys know don't know much about cars so any advise they give I usually pass on.
 
The precious metal plugs can be damaged if they're manhandled during gapping, which is why it's normally recommended not to gap them.

However, I always gap new plugs of any type. I just take it slow and careful when doing so (and use a "sloping edge" gap gauge instead of a "round wire" gauge).
 
I've found over and over that Bosch spark plugs are junk, unless you are using the bosch super or whatever their copper plug is. I've seen SOOO many issues with Bosch Platinum's causing driveability problems. I know that just as you should never seen 25hp or whatever a manufacture may claim their plugs will gain you, you should also not see any real problems caused by a plug that is in the same heat range and dimensions, but I've seen it over and over.

Anyway,

Many times if you look at NGK's plugs (which imho are the highest quality most reliable plug for ANY application) you will find that they offer their plugs either pre-gapped to a certain spec or un-gapped. The problem is that one of the two is usually a common stock item where the other one is not.

When I am working on my own engines, I also check the gap with feeler gauges. If I am working on someone elses engine I just look at them quick to make sure they are not slammed shut from dropping and then just install them.

From what I have seen over the years, with most vehicles that have not been modified run fine on whatever gap comes on the plug. Unless you are trying to stretch the gap out too far. Not all ignitions and setups will allow you to run say a .050 gap without misfires.

Anyway, chances are you could set one plug at .030, one at .040, one at .045, and one at .035 and would never notice any difference than if you set them all to .038 or whatever factory spec may be,
 
Originally Posted By: Johnny248
I've found over and over that Bosch spark plugs are junk, unless you are using the bosch super or whatever their copper plug is.
+1 on Bosch platinum being not good for most applications other than race or aviation engines; and Agreed that their "super" copper plug is a VERY good plug. I would disagree on NGK, their v-power made in USA are junk - tend to run hotter than the indicated heatrange and the GND electrodes wear way too rapidly. The Iridium plugs are excellent, especially almost a MUST on COP ignition with the marginal coils. Had great luck with the correct champion too. Caution on moving the GND electrode - dont fuss with it too much or you will change the metallurgy and the gap will creep out of spec when heated in the CC.
 
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First, I always buy Iridium Platinum, either Champion, ACDelco, or NGK, even Autolite (but they're not my first choice). I check carefully, whether the two electrodes are lined up - sometimes the ground does not line up, and needs to be bent sideways. Then the gap is carefully checked with the feeler gauge. I find that they a RARELY exact, and I spend about 30 minutes on a set of 4 plugs gapping them exactly. Even though the ECU will tolerate poorly gapped plugs, which is what you get out of the box, and what most mechanics will install in the shop, it is much better to do the proper job. For instance, if one plug is gapped too narrow, it might fire a little sooner, and this might result in a knock, activating the knock sensor, retarding the ignition, etc..
this is just a theory of mine, so please correct me if i'm wrong.
 
I always check them and adjust. I'm not overly picky about being *perfectly* gapped, but out of the box the gap can be all over the place. It only takes one guy dropping the box in shipping to un-gap all the plugs...
 
I check them, which turned out to be good the last time I changed plugs. I had heard that Motorcraft plugs were pre-gapped. They were...for a Modular V8 (.054), not for my 3.0 (.044).
 
First, avoid Bosch plugs unless they are factory exact types.

It is fashionable lately to assert that modern spark plugs should not be checked, and Heaven forbid you should ever regap them!
Nonsense. Just use care - be gentle. And also always check a new plug for continuity from the center to the end.
 
For the most part, I have not found a plug that is "junk".

Its just that certain brands work better for certain applications.

Bosch Super plugs were the hot item for my Volkswagen's. The car would not run right with anything less.

My Ford Motorcraft plugs are made by Autolite for the most part.

My new chevy ecotec Delco plugs are made by NGK, so I replaced with NGK. No problems..

In 99 percent of applications, just stick with the type of metal that the factory uses.

In my dodge neons, the thing would love copper Champion plugs.

Most of the new plugs come pregapped, do not gap them, I have messed up the metal tip doing this.

I consider the plugs a disposable item. You won't catch me pulling plugs to clean or regap. If I am going to invest time pulling plugs out of a motor, I am not going to put the same ones back in. The NGK platnium plugs I just bought were 3 dollars each.

There is no reason to get fancy $10 iridium wallet drain plugs.

I had a 96 thunderbird with a "bullitt" mustang gt motor and a supercharger. I ran 1 dollar autolite copper plugs (2 heat ranges colder of course)..

Every plug has its application.
 
All the fancy plugs I buy have polyprop sheath on them - no way to ding the gnd electrode
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I squint to make sure not dropped then in they go. Sometimes compare an old one vs the new ones, not much gap growth over 30k with cheap coppers....
 
Sometimes you take as much care as possible setting a gap, then ding them going down into that deep, dark hole in them new-fangled DOHC Injuns!
 
Originally Posted By: JustinH


There is no reason to get fancy $10 iridium wallet drain plugs.

Yes there is.

My 2003 Saturn ION had severe gap erosion at 60,000 miles with AC double platinum plugs.

My dad's 2007 Pontiac G6 had close to zero gap erosion after 80,000 miles.
 
I always check the gap on any plug I install. Takes a couple of seconds to do, and doesn't require one to try and figure out later why their is engine won't idle right after a tune-up.
 
As long as you dont metal-foul the insulator, then the Ir plugs are an easy 100K plug. Again: small coil COP ignition prety much REQUIRES an Ir plug to have sufficiently low misfire counts. If you have a mod inline 4 and like to or have to pull plugs then Denso hot-U or champion or bosch copper are good stuff. IMO Denso have the finest QC ive seen after wrenching 1000's of plugs. The Older subaru 1.8 and 2.2L lOVE the K20pru-11. I find some strange pre-ignition issues with certain Pt plugs. Recall that Pt wire will catalyse fuel vapour and become red hot - with the engine shut off!
 
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