Proper spark plug gapping technique

[WesChapman]

This isn't related to my Scout at this time, but the wife's 2005 Jeep liberty has become my daily driver. I was looking over the service records and realized it's about 30k miles over due for spark plugs. I've never been real confident that I gap plugs correctly. The Jeep needs to be gapped @ .035. What is the correct procedure and what mistakes should I watch for. Plug gapping seems like a simple little task, but as I've learned with other ignition components, sometimes the most simple items can be the most crucial to proper operation.
Thanks

 

[Michael Mayben]

Pros use a tool that is based upon a pair of pliers with a selectable "die" for the common plug gaps. That's a "production"-type tool that is of no use to a diy'r.

The acceptable method for a conventional "side-electrode" plug is to use a round wire gauge. But this is not rocket science and folks make a big deal out of something that is not critical to that extreme. One of the "wedge"-type gauges found on most parts counters works just fine, I use that nearly every day.

The "gap" is one of the major factors in determining the voltage required to ionize the plug gap each time the ignition system fires the plug for any one cylinder. There is a direct correlation to "gap" vs. "voltage required". But as long as you are within 0.005" of the recommended gap for the system being serviced, that is just fine.

Don't confuse "plug gap" which is not critical...with "point gap" (dwell) which is a critical measurement. Two entirely different areas of concern!

 

[RobertC]

As michael states -- this is not "rocket science".

I have always used the "round wire" tool as opposed to the "wedge" tool that michael uses - any auto parts stores should have both.

The "round wire" should not be "difficult" to insert in the gap. And, there should not be "play" in the gap.

One double check I use on the "round wire" tool is to check
that the next "bigger size" up does not fit in the gap.

The "wedge" tool will work perfectly well, also.

 

[Greg R]

Wire or wedge, the gapping tool has a hole or slot you grip the ground electrode, the part connected to the body with the threads, with to gently bend in the direction you need to go to widen or narrow the gap. Narrow pliers can work too, but I've ham handed a few with them. Here's a link with pictures, 4th & 5th one down; easier to show than tell.
spark plug replacement tech tip

Common mistakes can be wedging something tight between the electrodes, chipping the insulator, bending the ground electrode off center or flat out breaking it off.