How to Install a Spark Plug

By Deanna Sclar from Auto Repair For Dummies, 2nd Edition

4 of 6 in Series: The Essentials of Replacing and Gapping Spark Plugs

When you're changing your vehicle's spark plugs, work on one spark plug at a time: Remove it, inspect it, clean it, and — if it’s salvageable — gap it. Then replace it before you move on to the next spark plug in cylinder sequence order. To maintain the proper firing order, each spark-plug wire must go from the spark source to the proper spark plug. Therefore, only remove the wire from one plug at a time, and don’t disconnect both ends of the wire!

To insert a spark plug into the engine, follow these steps:

Clean the spark plug hole in the cylinder block with a clean, lint-free cloth.

Wipe away from the hole; don’t shove any dirt into it.

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Lightly coat the threads of the spark plug with a dab of oil from the oil dipstick.

Be careful not to get any oil on the center or side electrodes.

Carefully begin threading the spark plug into the engine by hand, turning it clockwise.

This is called “seating the plug.” You have to do it by hand or you run the risk of starting the plug crooked and ruining the threads on the plug or the threads in the spark plug hole in the engine.

If you have trouble holding onto the plug, you can buy a spark plug starter and fit it over the plug. Or, you can use just about anything you can wrap around or slip over the plug top, including an old spark plug wire boot, a finger cut from a vinyl glove, an old piece of thin plastic tubing, or a piece of vacuum hose.

Engage the plug by hand.

Turn it at least two full turns before using the spark plug socket and ratchet.

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Slip the spark plug socket over the spark plug, attach the ratchet handle, and continue turning the plug clockwise until you meet resistance.

Don’t over-tighten the plug (you can crack the porcelain); just get it in nice and tight with no wiggle. The plug should stick a little when you try to loosen it, but you should be able to loosen it again without straining yourself. Tighten and loosen the first plug once or twice to get the proper feel of the thing.

Examine the spark plug cable before attaching its boot to the plug.

If the cable appears cracked, brittle, or frayed or is saturated with oil, have it replaced. Before you attach the boot to the spark plug, apply some silicone lubricant to the inside of the boot; then push the boot over the exposed terminal of the new plug and press it firmly into place.

Repeat the steps to install each spark plug.

It’s at times like these that owners of 4-cylinder cars have the edge on those who drive those big, expensive, eight-cylinder monsters. Unless, of course, they have two plugs in each cylinder.

When you’re done, start your engine to prove to yourself that everything still works. Then wash your hands. If you’ve had a difficult time with a hard-to-reach plug, get some rest before taking on additional work. And take comfort in the fact that, next time, the job should be a breeze.