Rep Power: 0

All stock, including regular NGK plugs. What happens is the spark gap opens after time. I first noticed it when it was running poorly and would stall occasionally, replaced cap/rotor and plug wires, no help. Checked the gap, it was over .050" on all of them, took it back down to spec and it ran fine. Had a similar occurrence with my mother's '96 EX a while back.

Now I check the gap at every oil change (5000 miles) and all of them have opened up to some degree, usually around .048". It also runs progressively worse over the course of that 5000 miles until I regap them. Doesn't seem to happen to my mother's car, it has run fine since the last plug setting (though I haven't actually checked the gap).

Has anyone else seen this happen?

 
Rep Power: 520

On standard plugs, the gap opens up as the electrodes wear. That is why they are supposed to be replaced every 30k.

The expensive precious metal plugs wear the electrodes extremely slowly by comparison, that's why they are specified to be replaced at 100k.

 
Rep Power: 212

Which specific NGK model did you use?
Did you use a coin or wire style gapper?

Here some spark plug nerdery for you which may help: http://vdlfuelsystems.com/?p=273
and http://mechanics.stackexchange.com/q...uel-efficiency

 
Rep Power: 0

I put in the stock plugs, so probably ZFR5F-11 (I'm at work, can't go look right now). I see that the HX uses ZFR4F-11, I can envision an universe where I wasn't careful looking them up; what would happen with those plugs in my engine?

I use a coin-type gapper, I adjust it until the center of the electrode sits at .041".

What has me scratching my head is that I've used regular plugs in all kinds of cars for years well past 30,000 miles and have never seen any appreciable wear on the electrodes, nonetheless having to adjust the gap after the first installation (I've traditionally used Bosch Supers, a throwback to my air-cooled VW days). I'm just wondering if it indicates a problem or is just a characteristic of either the engine or the NGK plugs.

 
Rep Power: 520

Wear is typical of standard plugs. The 4F plugs would only be a heat range difference, not a wear issue.

 
Rep Power: 0

Like I said, the electrode does not show any obvious wear, it happened within 5000 miles on brand new plugs.