Rookie Spark Plug Question

A couple weeks back I changed out the likely 20 year old plugs with a new set of Champion N12YC. Fairly easy/straightforward exercise and the car instantly sounds smoother to my ears. I’ve driven a few hundred miles since and all is well.

An engineer friend asked if I had gapped them or set the gap and I had no idea what he was talking about. I had basically just taken out of the box and swapped (after a thorough cleaning of the surrounding area).

Of course, he then proceeded to lecture about a heavy carbon build up and all sorts of other perils.

Is this something I need to be concerned with or was he just grinding my gears?

It’s always prudent to verify the gap is correct when you install new spark plugs. The manufacturer has no idea what engine you are using the plugs in and different engines can require different spark plug gaps.


Hey Philip:
Perhaps it’s time to go shopping for a service manual? If you’re planning on performing your own maintenance it’s all in there including gap setting @ .025". It’s straight forward enough but you should be gapping the plugs or at least checking them. I have the Bentley manual but there are others. It’s a good way to get more familiar with the car and learn more about how it’s all supposed to work including procedures, technical specs, fluid capacities, etc. - it’s all part of owning a classic vehicle.

FYI, you’ll need a spark plug gapping tool as well.

Good luck. :sunglasses:


I actually have the manual… just didn’t realize this was a thing. Appreciate the tip and looking forward to figuring it all out.

There are at least two very different tools for this. One is a disc with a ramped gauge that tells you the gap, the other has assorted wires with various thicknesses to use as go no-go gauges. Both work and both have a means of prying on the side electrode to change the gap.



Worth getting, learning and using but you will probably find those plugs are very close to the prescribed gap.

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99.8% of the time, the gap out of the box is close enough.

This is another area where overly–OCD folks drive themselves bananas, trying to get all the plugs within 0.001".

Keeps’em off the streets, I suppose…:sunglasses:


:rofl: A little early in the day to be drinking eh Wiggs?


Wiggs is a teatotler. He’s just practicing his Klingon.


Shall we get into indexing :rofl:

Fixed it: the Drambuie wore off…:crazy_face:


To the new guy……do NOT forget to put anti-seize on the plugs when you install them.


That part I got right!

and only do one plug at a time, don’t pull all the plug wires off and then try to figure out who went where. Do you have a torque wrench?
two videos on gapping:

and this one on torquing the plugs. You just don’t want to tighten them too much, or, too little.

I often use a valve gap tool, a feeler gauge. Got reamed verbally for why not to use it, but I like to double check the plug gap. That round dial thing looks suspect and the feeler gauge set I have has the side tool for opening/closing the electrode. I use this tool on the plugs for my cars, old boat, lawn care equipment, etc. They all start right up and run great.

gap tool


People still drink that?!:see_no_evil:

I did only do one at a time, but also found that with the plug wire harness it’s nearly impossible to get confused on the proper order, but I was extra careful. I did use a torque wrench to tighten, but couldn’t find the spec. Someone told me it was around ten pounds. I set mine at 7.5 and still didn’t get a click. I decided to go by feel. They are snug but not crazy tight,

I did buy a dozen plugs, so I’m just going to check the ones I didn’t use before redoing the job already done.

I screw the plugs in with a sparkplug socket and 3/8 ratchet. Going slowly I can feel when the crushable gasket contacts the head and the gasket is crushing. The effort suddenly increases when the gasket is fully crushed. That’s where I stop.

NGK says not to use anti-seize.


There is some controversy on anti seize. A good way to prevent the plugs from seizing is to removed them on a regular basis just to check, even if not replacing. That is often done on newer cars, they are regularly removed every 100,000 miles!!!

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FWIW–mainly out of laziness–I haven’t used anti-seize on NGKs in my last 4 cars, and the plugs popped out just fine, when needed.

Anti-seize usage…I’ve never investigated whether the stuff is good or bad and perhaps more importantly, why. My avid use of it stems from the years of advice from this and other sources that talk to its need on plugs to prevent them seizing up in the alloy head…

I’ve owned my Jag for 25 years and always used the stuff and never had any kind of problem…however, next time the plugs come out I’ll clean them off…maybe my annoying rough idle problem will go away…;-0

Is it wrong that I put a tiny bit on the wheel hubs when I swapped in winged caps?