Seized-Part Job · Car & Truck

How to Remove a Stuck Spark Plug from an Aluminum Head

Steel in aluminum. A delicate situation that rewards a gentle hand.

Steel plugs in aluminum heads can seize, and forcing them pulls the head threads out with the plug. Slow, cold and patient is the rule. If it is badly stuck, stop and look up your engine. Some have known plug-removal procedures and special tools.

The Method

Step by Step

1
Engine cold
Let the engine cool completely. Aluminum expands more than steel, so a warm head grips the plug harder.
2
Blow out the plug well
Use compressed air to clear debris from around the plug so nothing falls into the cylinder.
3
Soak down the well
A small amount of penetrant down the well onto the plug threads. Wait at least 15 minutes, longer if it is badly stuck.
4
Turn a little, then back
Loosen a quarter turn. If it gets tight, turn it back in, add a drop more penetrant, and work it again.
5
Stop if it gets tighter
Steadily rising resistance means the threads are galling. Stop and get help before the head threads come out.

Heat call: No heat

No external heat. Remove plugs from aluminum heads with the engine cold so the soft head threads are not damaged.

Safety

Use only a small amount of penetrant. You do not want a pool of it in the cylinder.
Crank the engine with the plugs out before reinstalling, to clear any penetrant from the cylinder.
Torque new plugs to the plug or engine maker’s spec. Over-torquing is how this started.

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