Spark Plug Gap Adjustment

Hey - I have a problem tractor and am going through and replacing a bunch of stuff and learning along the way. I am replacing spark plugs. Its a 1971 FORD 4400 gas. Spark plugs on this site and Steiner say AL405. This comes with a pre set gap of .035. Spec for my tractor says .025. Is it common to adjust the pre gap setting when replacing plugs or what am I missing here?

Thanks!

Yes. Setting gap is normal procedure.

Is it as simple as bending over the bottom piece to the .025 spec? Anything I should be aware of?

Best to have proper tool. Don't break the porcelain when adjusting.

(reply to post at 20:38:16 06/20/23)

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Looks fancy, with fancy $55 price.

Have installed a thousand, never any tool to close the gap other than the my finger and thumb and a solid surface to tap the gap.I

And one of these if I tapped a bit to much

They all seem to be gapped different. I check and adjust the gap on every plug I install.

Oem was Autolite AG5 set at .025 Champion N-14Y. them numbers have all been changed.

Thanks for the tips and all the info. Will give it a try

As a general rule, never trust plugs to be pre-gapped. Even if they are (supposedly), i would not trust them to be properly gapped. Keep in mind that the same plug can fit MANY other applications, and not all applications call for the same gap. That has to do with ignition system design and manufacturer testing.

what your missing? them plugs might be for electronic ignition. many old tractors were .025. i have changed piles and piles of plugs in all kinds of engine. when you get the correct plug there is no way they vary by .010 gap. only maybe a couple thou. years ago oldsmobile had a gap of .080 and that is what the gap was when you replaced with new plugs. i always run a guage threw new plugs. if the gap was .060 that is what the plugs were. i have yet to find gaps being out that much for the correct plugs. whos plug is that AL405? and yes plugs are pregapped.

Yesterdays tractor and Steiner both state they sell autolite 405 plugs for this tractor with a gap spec of .025. While checking to see if I can get these same plugs at naps, oreilly, or auto advance they all see the spec is .0345. For timing purposes id prefer to just run to my local parts store and grab them.

Would you have a look and give me your thoughts? I thought it was odd, which is why this post was created.

Tractor is ford 4400 1971 3cyl gas

Been years since I bought plugs BUT I NEVER HEARD OF PREGAPED plugs. You always checked and adjusted every plug before installing it. Normal to find every plug in bunch set different.

Pre gapped is how they are described on the auto parts sites. Its all new to me

There's no problem/issue with gapping conventional spark plugs, just try to keep the ground electrode ''face'' perpendicular to the center electrode.

In the other hand, fancy modern platinum, iridium, etc. sparkplugs typically come with a warning not to mess with the gap or the exotic material bonded to the center electrode or ground electrode can be damaged or scuffed off entirely.

that is totally not normal unless they got dropped . they are always gapped. tell me how they can build plugs with different gaps in the same class. never even heard of such a thing. as i said they might vary by .001 0r .002 never by .010. soon as you open them up or close the gap the tab is no longer square to the electrode.

My experience - ... plugs are generally close when new and out of the box. I check the gap on every one before install. If they are off a few thousands, I simply adjust the gap to what I'm doing (what the book says).

I'm not going to jump into the pre-set or not arguement. But I will say this. If you are adjusting the plug gap by alot (15 or 20 thousands), you are likely adjusting the plug gap further than intended. Unless per-say the plug was dropped on the floor and bent the ground tab into the electrode. Then you'd obviously have to open the gap back up along with inspecting the porcelain.

That said, adjusting 5 thousands is not un-common. I don't think I'd be afraid to adjust as much as 10 thousands. The further you adjust, the more out of square the tab will likely be to the electrode. But the proper gap is more important than squareness (in my opinion). If it's out of square, what's it gonna do? Shorten the life of the plug a bit? If a miss developes as a result of burn off, you should just be able to adjust the gap again. Right? All you really need it to do, is spark. No need in throwing rocket science at a 71 Ford 4400. Just saying.

I've had to adjust plugs on lots of things with new or used plugs as they get dropped or bumped and are off also most plugs are pre gapped for automotive uses since the loins share of them are used there and may not be the same gap as these old tractors. IF one plug is fouling or goes to missing you can give it a bit more gap and it wil help keep it from fouling as quick. I had an old Plymouth that would run better with about .045 gap than the .035 or what ever it was supposed to be set at. Was an old tired engine and used a bit of oil.

If they are all that way it might be a new spec or possibly the wrong plug. If one is that way it might be qc issue. Pregapped ones should come with a little cardboard sleeve over the threads that protects the gap. They sell fancy iridium and platinum plugs now too that the parts salesman will push if you go to the counter. Still only last the same 50000 on the pickup and need replaced.