How to remove a broken spark plug

Typically spark plugs are not difficult to remove as long as the plugs are replaced on a regular basis. But spark plugs can break off, particularly in engines that have been sitting for long periods of time. This is why you hear the plight of broken plugs being raised by antique tractor restorers.

Understand that a spark plug is constructed like a hollow bolt. If you exceed the recommended torque during removal, the spark plug shell can shear off below the installation hex head, says Champion Auto Parts.

If excessive force is required to remove a plug this can be traced to one or more of the following causes:

• The plug was left installed for too long a time.
• Someone installed the spark plug using excessive force.
• Someone cross-threaded the plug during installation.
• Someone installed the plug with dirty threads. To avoid this always clean the threads on plug you have removed to clean their tips and electrodes and then coat the threads with anti-seize compound. This is especially important with spark plugs being installed in an aluminum cylinder head or in equipment that is stored outdoors.

The most common way to remove a spark plug which has twisted off above its hex head is to use an extraction bit, which is often called an easy out bit.

Champion Auto Parts highly recommends only using a square-cut bit as opposed to a spiral-cut bit (see illustration below).

With a spiral cut bit you risk a greater chance of causing the broken spark plug’s shell to expand, locking it even tighter into the cylinder head as removal pressure is applied.

On the other hand, the square cut type bit employs a sharp flute that digs into the broken plug shell to provide a strong gripping surface without expanding shell metal.

But before you attempt to remove the plug be sure to rotate the engine so that the piston located below the plug you are removing is at bottom dead center. Also make sure the engine is cold.

Next soak the broken plug shell with a generous amount of penetrating oil. After soaking go enjoy a cup of coffee or tend to other shop chores. The key is to allow the penetrating fluid to seep into the plug’s threads.

Now employ the spiral cut easy out bit (using the appropriate bit size that fits firmly into the empty spark plug shell).

Brace yourself while using ratchet so that the ratchets drive fits squarely on the easy out bit. Apply firm, steady pressure in a counterclockwise direction.

Although the required installation torque to remove a taper seat spark plugs is only 7 to 15 feet pound, Champion Auto Parts report they have heard reports of successfully removing a broken spark plug using torques exceeding 180 foot pounds.

Here is a reader tip on how to remove a broken off spark plug:

Maurice Pederson recently had the frustrating experience of twisting off a spark plug in his John Deere Model A. “This is not a case of restoration, since I have owned this jewel for over 40 years,” the Valley City, North Dakotan relates. “It was running good, but I knew it was weak on one cylinder, so I decided to do a valve job on the tractor. After I got it running again, I thought I might as well check the spark plugs and ignition points. When I put the wrench on one of the plugs, I was really surprised to find out I could not move it.”

Pederson continued to work on loosening up the plug until. . . . yes, you guessed it, “it twisted off just below the next part of the plug body.”

Not wanting to have to remove the tractor’s cylinder head to remove the spark plug’s base, Pederson improvised a solution you might be able to use.

First, he ground a hacksaw blade down so it would fit through the plug’s body. Then he positioned the blade in a bayonet-type handle using it to cut a slot through the spark plug body so it would collapse.

Prior to cutting, he positioned the handle so it would cut on the pull stroke. “I cut the slot deep on the innermost threads because I didn’t want to damage the outer threads,” he says. “I ran the thread chaser in to clean up the threads” after collapsing and removing the plug.

Before installing a new plug, he started the engine to eject any foreign matter so it wouldn’t get caught in the exhaust valve.