I don't know why, but I can't for the life of me figure out what head size is on the spark plugs in my car. I know the owner's manual says 14mm, but I have tried every single size both metric and SI, yet NOTHING is grabbing.

What am I missing here? Is there something special about these plugs? I've changed plugs hundreds of times and never ever had an issue like this.

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1963 Plymouth Fury 4-door, 225 /6, 3-speed manual w/ OD, "super six", Mopar electronic ignition

If it's a pre-77 head, then 13/16" is the size. You need a deep well socket.

Lou

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Home of Slant6-powered fun machines since 1988

Thanks so much, I'll give it another shot...with all the sockets I have, I get the feeling 13/16" is the only deep well I DON'T have...go figure.

Can't just be 5/8" like 90% of the vehicles out there huh? Or even 14mm like the manual says.

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1963 Plymouth Fury 4-door, 225 /6, 3-speed manual w/ OD, "super six", Mopar electronic ignition

Could it be that the outer diameter of you plug socket is too big to reach down far enough, or that there is something lodged down in the tube that shouldn't be there, have you experienced the same on several plugs?

Olaf.

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Aspenized

GOT IT!! Thanks guys....and holy crap are these plugs fouled...NGK VR4, and only gapped at .031.

This would partly explain my extremely crappy idle, and intermittent hesitation when I'm on the gas.

Always liked NGK plugs so I may just directly replace them, or go with Champions.

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1963 Plymouth Fury 4-door, 225 /6, 3-speed manual w/ OD, "super six", Mopar electronic ignition

14mm is the thread size, not the hex size. The plugs you're taking out are 13/16" hex. The ones you should put in (NGK ZFR5N, stock number 3459) are 5/8" hex. Use a spark plug socket (w/rubber insert), not just a regular deep-well, or you're liable to break off a spark plug and cause yourself much more hassle than it would be to get and use the correct socket in the first place. Tune-up parts and technique suggestions in this thread.

Whether you follow or ignore the plug recommendation, remember to remove the metal ring washers from the plugs before installing.

Champion is junk from America. Autolite is junk from China. And if you've fouled NGK #4s, there's something the matter -- #4 is hotter than called for.

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一期一会
Too many people who were born on third base actually believe they've hit a triple.

Thanks Dan, this is the first chance I've had to change the plugs since I got the car, and these plugs seem to have been in there for a long time. I've gotta go out and get a 13/16" plug socket, got plenty of 5/8" though haha.

The NGK's I pulled out also had the washer still installed on them...could also be another part of my "off" performance.

Is there a prefered method for removing the washer, or just a dremel and some TLC?

EDIT to above, just read it.
EDIT #2, how do I verify the head is in a certain year range? This car has had a super six conversion but don't know if anything was done to tbe block/head at that time.

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1963 Plymouth Fury 4-door, 225 /6, 3-speed manual w/ OD, "super six", Mopar electronic ignition

It'll make 'em run hotter than normal.
Grasp with slip-joint pliers. Unscrew plug from washer.
Don't bother. The odds are super-slim that you have a '60-'62 head on your engine. Just go ahead and install the plugs without the washers.

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一期一会
Too many people who were born on third base actually believe they've hit a triple.

My other question would be, if I did replace with an off the shelf model of spark plug from NGK, what would it be? The Z5FRN is not available anywhere around here and I need this car to be up and running by Sunday....I have options for V power and G power (which is platinum and I don't believe I want)

In any event, the washer will be removed no matter what brand/model I go with.

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1963 Plymouth Fury 4-door, 225 /6, 3-speed manual w/ OD, "super six", Mopar electronic ignition

You sure? Pretty common plug used in many many recent Mopars. See if they find it by asking for NGK plugs for a 2000 Jeep Cherokee with 4.0 six-cylinder engine.

If you're stuck and can't get the good ones, get a GR5.

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一期一会
Too many people who were born on third base actually believe they've hit a triple.

Luckily enough, the Advance Auto Parts right up the street just got some of the ZFR5N plugs in today, so I was able to pick them up for $15.

Just need a fuel filter and new gasket for my air cleaner cover and I'll be all set.

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1963 Plymouth Fury 4-door, 225 /6, 3-speed manual w/ OD, "super six", Mopar electronic ignition

Got the plugs gapped properly to 0.040" but am having trouble with the washers....any tricks to getting these things off? I used a pair of pliers to grab the washer but it doesn't exactly "thread off"....I don't want to damage the threads.

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1963 Plymouth Fury 4-door, 225 /6, 3-speed manual w/ OD, "super six", Mopar electronic ignition

Throw more mustard (muscle) at it, you won't hurt anything. The nice-quality washers NGK uses are harder to unscrew than the pathetic ones you get with Autolite, Champion, etc.

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一期一会
Too many people who were born on third base actually believe they've hit a triple.

I grab the washers across their thickness direction with a needle nose and twist them until they break off.

Lou

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Home of Slant6-powered fun machines since 1988

Got everything done ok, just took my time and un-threaded the washers, works a lot better when you're in a patient mood haha.

Replaced the plug wires while I was at it too, the AutoLite wires worked perfect, and are 7mm as needed.

Should the inside of each of the tubes be cleaned when replacing the plugs? I just took a towel and wiped out all the dirt and bugs that were crammed in there.

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1963 Plymouth Fury 4-door, 225 /6, 3-speed manual w/ OD, "super six", Mopar electronic ignition