How To Rethread A Spark Plug Hole? [Easy Guide]

Run a spark plug thread chaser to rethread your car’s spark plug hole. It’s important to note that it should match the size of your vehicle’s socket.

If the threads are severely broken, a threaded insert kit will be required. 

Next, thread the oversized threaded tap with bearing grease to catch thread shavings, allowing you to make new threads. Install the threaded insert onto the installation mandrel at the end.

Why Would You Need To Rethread A Spark Plug Hole?

Three main factors that could cause damage to the threads on your spark plugs include:


Tightening your spark plugs too much will cause a loose thread, damage the internal components, potentially contaminate your engine with thread shavings, etc.


If you ever install your spark plug at a bad angle, it will damage the threads.

Stripped Spark Plug

A stripped spark plug means that the teeth meant to go into the threads in the spark plug hole are damaged.

How To Rethread A Spark Plug Hole

YouTube video

The process starts by having to rethread the spark plug hole with a rethreading kit. A rethreading kit should contain a rethreading tool, thread inserts, and spark plug screws in the insert.

In the video, the narrator begins by attaching the rethreading tool to a socket extension and slowly making new threads into the spark plug hole with a socket wrench. It’s important to go slow to ensure the best results. 

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Once the tool bottoms out, unthread it to retrieve the tool.

After retrieving the tool, you can install the thread inserts into the new threads. This video also includes a helpful tip if you have difficulties installing the thread inserts. 

Finally, when installing the new thread inserts, you can now install your spark plug. 

Frequently Asked Questions

How much will it cost to rethread spark plug holes?

The cost of repairing a spark plug thread depends on whether a temporary repair kit is used and whether the operation is performed by yourself or by a professional. Generally, it can cost anywhere from $20 to $1,000.

What will happen if spark plugs are too tight?

It would be difficult to remove and might harm your cylinder head. In the worst-case scenario, nothing will happen. 

Additionally, it may even look like the spark plug has fused with the cylinder head. Deposits, dirt, and possible corrosion can stick together like glue. 

You must not damage the bolt hole in the cylinder head. A replacement cannot be placed if it is stripped or otherwise distorted.

Damaged fragments of the spark plug insulator or electrode might enter the combustion chamber. They can bang about and damage the parts and surfaces they encounter.

How tight do spark plugs need to be?

Tighten the spark plug with your fingers until the gasket touches the cylinder head, then use a spark plug wrench to tighten it another 12–23%.

Obviously, they must be tight as plugs close off the combustion chamber. When a plug breaks loose, cylinder compression is lost, and the cylinder inhales oxygen on the downstroke through the loose plug.

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