A couple months ago, a mechanic in attempting to assist me with a few small ideas, replaced my plugs. I just changed them out yesterday after about 6 months or so, and to my astonishment, this was the results in the gap: 1-5=.046 6=.036 Yea, he messed up. The situation is this: 1-5 had a blister on the side of these truck plugs and were rounded off on that side. 6 was in near-perfect condition.

Anyone ever try changing the plug gap to something smaller than what's printed on the firewall sticker? I really want to try making them all about .036-.038 and see if it still runs.

Timber

 

You want as wide a gap as possible providing your coil still has the power to jump the gap. This gives you the most spark exposure for the most complete burn (at least that's the way I understand it).

'82 F150 2WD w/351W (orig 300 I6)
Slik

 

I think you ll find a gap of .046 is the best . Describe what this blistering looks like , color etc . Its fairly common for the Motorcraft plugs to burn down the sides like you described . How many miles on your engine ?

 

Hi. Well, the blistering looks like I may have taken a torch to the side of the porcelain. It actually is bulged out, black/grey looking, and looks like ash. The side of the electrode is rounded off severely also, on the side of the blister. The engine has about 61.5k miles on it.

One idea, though. If the gap is too large for the coil or whatever, could it be that the compression is forcing the spark off to one side? All {1-5} look the same, exactly. So, if I shorten the gap a few, say to about .038-.040 {remember that the #6 was .036 when I took it out}, the spark would be shorter, hotter, and less likely to burn off one side? I'm really tempted to take them all out this Saturday and do just that, unless talked out of it.

Thank you kindly,

V/R
Rick

 

The wider the gap, the hotter the spark since it takes a hotter spark to jump a wider gap. And yes there are limits.

'82 F150 2WD w/351W (orig 300 I6)
Slik

 

The size of the gap has little to do with spark temperature but it has a lot to do with spark exposure, and yes a big gap gives more exposure ( for the nth degree in exposure read the posts on side gapping scattered throughout the forum, it works)The effect of gap size goes like this; A large gap (wider than stock) will actually blow out like a candle at high revs causing a high speed miss. A small gap (smaller than stock) won't give enough exposure at idle, causing a rough idle. The Ford six is designed to operate at lower revs and therefore the need for a wider gap...., But wait! There's more! Engine conditions vary widely and the stock gap is a recommendation at best. You can safely change these settings to suit your engine/climate/fuel/modification conditions, but I wouldn't deviate more than .002 from stock.
The problem your encountering is being caused more by the temperature range of your plugs than by the gap, if your burning the insulator then you need to switch to a cooler plug, then experiment with the gap to see what works best for you. I'd bet the stock gap on a cooler plug is what you'll settle on though...,FYI the Ford six's plug gap is one of the widest in the industry.
The temperature of a plug is a function of how far the thing actually extends into the cylinder, the further the hotter,and this temperature isn't the spark temperature it's the actual operating temperature of the plug itself. Hope this helps!

 

I use copper core plugs and gap of .50, and it runs great.