How to remove and replace spark plugs

Tips and tools to remove and replace spark plugs

If you’ve never changed spark plugs before, this post provides really important information on the best way to remove spark plugs to help you avoid the most common DIYer mistakes. I’ll cover everything from “spark plug hygiene” to how to gap spark plug and how to deal remove stuck spark plugs.

Get the right spark plug tools

You’ll need a spark plug socket to remove spark plugs and replace them

A spark plug socket is really just a socket that’s deep enough to slide over the entire tip and porcelain area and still engage with the hex portion of the shell. In addition to the added depth, most spark plug sockets also include a rubber insert that keeps the socket centered over the plug, preventing the socket from twisting and breaking off the porcelain section. However, some spark plug sockets contain a magnet that does the centering and helps lift the spark plug out of the hole once it’s unthreaded.

Spark plug socket and insert

Spark plug socket sizes

13/16” and 5/8” are the two most common sizes for older automotive and outdoor power equipment engines. However, the newer engines require small spark plugs.

• 14mm  for the latest European and Asian vehicle and motorcycles
• 12pt thin-walled for many late model BMWs
• 9/16″ for some Ford engines
• 5/8″ or 16mm for newer vehicles (GMC, Nissan, Chevy, Subaru), small engines (Briggs & Stratton, Koehler)
• 11/16″  Older BMW
• 18mm  Motorcycles and some small engines
• 3/4″ Lawnmowers, small engines, older GM vehicles
• 13/16″  Older vehicles (large engines.
• 7/8″      Tractors, older vehicles, aviation

6 point versus 12 point spark plug sockets

Spark plug sockets are available in 6-point and 12-point versions. Both work well on new and slightly used spark plugs. However, if you’re trying to remove a rusted spark plug, a 12-point socket is more likely to strip off the rusted corners of the spark plug.

Specialty spark plug sockets

You’ll often be working in tight quarters and that’s where flex and extra deep sockets come in handy. The problem with tight quarters isn’t so much in inserting the socket into the engine as much as removing the socket and plug. For example; many overhead cam engines have spark plugs buried deep into the cylinder head. You can use a straight socket and an extension to reach into the spark plug tube, but as you try to remove the plug, the extension often disengages from the socket. That’s where a single extra deep socket comes in handy because it eliminates “fishing” the smaller socket and plug from the spark plug tube.

A spark plug socket with an integral flex joint also comes in handy for use in tight spots.

Straight, flex and extra deep spark plug sockets

You’ll need a good ratchet to remove and replace spark plugs

You’ll need extra leverage to remove spark plugs buried deep in the engine compartment. A bent handle with an integral flex head is the best tool for the job. It’s longer than a normal ratchet and the flex head allows you to maintain the leverage while still fitting into tight places

Ratchet handle types

You’ll need a wire spark plug gap gauge to check spark plug gap

There are two types of gap gauges; wire and tapered. The tapered gap gauge seems easier to use since you just slide the tapered edge between the center electrode and the side electrode and force the gap open using the tapered edge. That design worked well on older copper spark plugs. But it doesn’t work well on newer platinum and iridium-tipped spark plugs. On those plugs the precious metal is welded to the tip and the tapered gauge can literally break the tip off the center electrode. If you own a tapered gauge, throw it out. Always use a wire gap gauge.

You’ll need dielectric Tune-Up Grease to replace spark plugs

Dielectric grease is an insulator and a lubricant. Apply it to the inside of the spark plug boot or coil boot to prevent the high voltage from firing down the side of the spark plug. As an added bonus, the dielectric grease prevents the boot from welding itself to the porcelain, making it much easier to remove the boot at the next spark plug change.

Squirt a small dollop of the dielectric grease into the spark plug boot and spread it around the inside of the boot with the tip of a clean Philips screwdriver.

Don’t use anti-seize on spark plug threads

When long-life spark plugs were first introduced, spark plug manufacturers recommended applying a light coat of anti-seize compound to the spark plug threads to prevent them from seizing in the cylinder head. That recommendation is now obsolete! Modern spark plugs come from the factory with a nickel plating to prevent seizing in the cylinder head. If you apply anti-seize on top of that coating, chances are you’ll over-torque the spark plug and distort the metal shell, causing the spark plug to leak and misfire. Do NOT apply anti-seize to a spark plug unless specifically recommended by the plug manufacturer!

You’ll need a torque wrench to replace spark plugs

Engine manufacturers have always listed a torque spec for spark plug, but nobody ever used a torque wrench. But that was back in the days when all cylinder head were made out of cast iron. Today they’re mostly aluminum alloys. If you over-tighten or under tighten a spark plug in an aluminum head, you can damage the threads in the cylinder head, or break the speak plug seal between the metal shell and the porcelain. I’m not kidding about this, you can do serious engine damage costing hundreds of dollars by improper spark plug torque.

So, use a torque wrench OR use the tightening charts provided by the spark plug manufactures.

The recommended spark plug torque is based on the type of plug seat; gasket or tapered, cylinder head material, and size of the plug. Here’s a chart from NGK.

If you don’t have a torque wrench, follow this guide from spark plug manufacturer AUTOLITE for how to tighten by hand.

Click on image to view PDF

Proper engine temperature for spark plug removal

Carmakers always recommend removing and replacing spark plugs when the engine is COLD. That way, the spark plugs, and spark plug threads have the least amount of thermal expansion, so removing spark plugs is easier and there’s less chance of damaging the spark plug threads.

If you remove spark plugs from a hot engine with an aluminum cylinder head, you risk tearing the threads out of the head.

Clean the spark plug area before removing the plug

Whether you‘re working on a car or truck engine or a small engine in your lawnmower, always clean around the spark plug hole before you begin removing the spark plug. That prevents debris from falling into the cylinder once the spark plug is out. And, it allows the new spark plug to start threading smoothly.

Blow the crud out of the area with compressed air before loosening the spark plug.

1) Remove the spark plug cable or coil pack
2) Loosen the spark plug with the proper socket
3) If the plug doesn’t budge, DON’T apply brute force. You’ll break the plug. Follow this procedure:

1. Apply a liberal spray of rust penetrant (WD-40 is a general purpose lubricant. It is NOT a rust penetrant. Use a real rust penetrant like PB Blaster, Liquid Wrench, or OR WD-40 Specialist Rust Penetrant.)
2. Allow it to soak for 30 minutes. Then try to remove. If you can get it to budge, STOP and apply more rust penetrant. Let it soak for 30 minutes. Then tighten the plug to work the penetrant back into the threads. Continue spraying, unscrewing/tightening until the plug comes out.

Install the new plug, following the torque guides above. Do NOT apply anti-seize to the spark plug threads unless specifically directed by the spark plug manufacturer.

©, 2021 Rick Muscoplat