How To Tell If A Spark Plug Hole Is Stripped?

If you are a car owner or mechanic, you will agree that spark plugs are essential for gasoline-powered engines. It provides the spark needed to ignite the air-fuel mixture in the combustion chamber. However, it must be in good condition and correctly tightened to function well.

If you have low-end spark plugs that require changing more often, you can strip the spark plug hole during replacement. But how do you tell if the plug hole is stripped?

A stripped spark plug hole will feel as if the plug is not catching the thread, or it’ll thread in but will never get torque.

This article will explain other ways of how to tell if a spark plug hole is stripped, the possible causes, and how to fix a stripped spark plug hole.

spark plug keeps turning

What causes stripped spark plug hole?

While stripped spark plug holes don’t happen often, several factors can be the leading causes. Damaged spark plug hole are typically caused by cross-threading, overtightening, and using the wrong spark plug size. Here’s a more detailed explanation.


One of the most common causes of stripped spark plug holes is over-tightening. If you over-tightened a spark plug, it could strip out the thread on the head cylinder. Aside from damaging the spark plug holes, overtightening can cause the plugs to become stuck in the holes, difficult to remove, and could even break the spark plug in the cylinder head.


Cross-threading is another common cause of stripped spark plugs and plug holes. Car owners and mechanics cross-thread spark plugs by threading the plugs from an angle. Putting a plug into the plug holes and tightening it with a plug spanner without snugging it by hand first will likely cause cross-threading.

This can stick the plug in the hole. It won’t get tightened, and it won’t come out. Removing cross-threaded spark plugs can be difficult without a stripped spark plug removal tool.

Worn/damaged or wrong size spark plug

Another possible cause of a stripped spark plug hole is using the wrong size. Ordinarily, using the wrong size spark plug won’t strip the spark plug hole. It’ll only strip the plug hole when forcing it to sit correctly.

If the spark plug thread is worn or damaged, it can strip the hole thread when tightening it. If you pay attention to details, you can quickly notice a worn spark plug and prevent it from damaging the plug hole.

For instance, if you always hand-tighten plugs before torquing them with a handle socket, you will know if you have worn or damaged spark plugs, and you will also know if you are using the wrong size. Wrong size, worn or damaged spark plugs won’t tighten smoothly with only socket and extension unless you use handle socket.

How To Tell If A Spark Plug Hole Is Stripped

How to tell if a spark plug hole is stripped

If you pay attention to details, you’ll know when the spark plug is stripped. There are common signs that show you have stripped spark plugs. They include the following;

  • When tightening a plug into a stripped plug hole, the plug will feel as if it is not catching the thread, or it’ll thread in but will never get torque.
  • If you visually inspect the spark plug hole and the hole feels stripped, you likely have a stripped spark plug hole.
  • If the plug doesn’t thread in easily without gently applying force, you probably have a stripped spark plug hole.

How do you fix stripped spark plug hole?

Don’t panic if your spark plug hole is tripped and can’t hold plugs. It is a fairly common issue that anyone can address with the right guide.

For this repair, you will need a spark plug hole repair kit. The kit will contain a tap, a drill, wall inserts, and an installation tool, commonly called a mandrel. You can get the kit at any auto spare parts store. The most interesting part is that the kit will cost you lesser than what a mechanic will charge you, and the tool will be in your toolbox.

Step 1: Remove the plug

The first step is to remove the spark plug from the stripped hole. Once the plug is out, clean the stripped threads in the hole using your tapping tool. Grease the tapping tool to avoid letting aluminum shavings fall into the engine. This part is essential because if aluminum gets into the engine, it will cause catastrophic damage.

Step 2: Cut the new threads

The next step is sticking the tap into the plug and cutting the new threads. Slowly turn the tap inside the plug hole for smooth cutting and to avoid causing more damage.

Use the old threads as references when cutting and drilling the new ones to ensure you get the proper alignment. Thread the tap tool into the plug hole and slightly oversize the cutting.

Step 3: Screw the thread inside the hole

The final step is to screw the thread into the plug hole. Get the thread and insert it on the mandrel and screw it into the plug hole. Clean the plug hole to ensure there are no aluminum or metal shavings in it.

You can clean it by rubbing grease on the tap and cleaning the hole. But the best trick I learned over the years is to start the engine and let compression blow out all the shavings in the hole.

You are almost there. Get a new set of spark plugs, and you are good to hit the road. Watch this video for a visual reference. This will also be helpful if you are looking for how to rethread a spark plug hole on a lawn mower.

Frequently Asked Questions – FAQs

Q: What do you do when your spark plug hole is stripped?

Stripped spark plug holes can be dangerous. It can cause the plug to shoot out of the hole and damage the ignition coil or plug wire. You don’t want a minor issue to escalate before repairing it.

If you have a stripped spark plug hole, the most feasible solution would be to re-thread the hole using a spark plug repair kit. You can also contact your mechanic to fix the stripped hole if you are not a DIYer.

Q: How much does it cost to fix a stripped spark plug hole?

The cost of fixing a stripped spark plug hole varies wildly from as small as $110 to $1,000. It all depends on who is fixing the stripped hole and the severity of the damage. If you choose to repair stripped spark plug threads on aluminum head yourself, you’ll spend $75 on the repair kits and $30 on new spark plugs. But if you want your dealership to fix it, budget around $750 to $1,000.

Q: Can you drive a car with stripped spark plug?

While you can drive with a stripped spark plug, depending on the severity, don’t do it. You can doesn’t mean you should. If you don’t replace the stripped spark plug and continue driving with it, you will cause more damage to the spark plugs and the cylinder head.

Q: How do you get a stripped spark plug out of an engine?

Removing stripped spark plugs from an engine can be a pain in the ass for both mechanics and DIYers. This, however, doesn’t mean you can’t remove it. You need two items to remove a stripped spark plug. This includes a nut/bolt extractor and a penetrating oil like WD40.

All you need to do is to spray a WD40 into the plug hole and allow it to sit for a few minutes. After that, insert the nut/bolt extractor and loosen the stripped spark plugs. Blow a heat gun into the plug hole if it is too stubborn to come out, and take it out with the nut extractor. Watch this video for visual clarifications.

Can a spark plug hole be repaired?

Yes, you can repair stripped spark plug hole instead of scrapping the cylinder head. Fortunately, this isn’t a major job that requires taking off the cylinder head from the engine block. Mechanics can repair it in less than two hours, depending on the damage.

Final Words

Car maintenance can be frustrating and unnerving at times. But if you have the right tools, the right guide, and the required skills, it’ll be a lot easier and even fun!

Now that you have learned how to tell if a spark plug hole is stripped and how to fix it re-read this article from A-Z and watch the attached videos for visual clarification. After that, roll your sleeves, get your hands dirty, and have fun.



While growing up, I knew I had a thing for car repairs though my parents never wanted me to learn mechanics. I always visit a mechanic garage in my small neighborhood after school. As I grew older, at age 16, I got addicted to anything automotive. My parents had to enroll me in that mechanic garage since giving up was never an option for me. As a dedicated mechanic who got into the industry from an early age, I'm graced with an addiction to diagnosing and rectifying automotive problems with ease.

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