How to Fix Spark Plug Thread and What Is the Repair Cost

The spark plug thread plays an integral part in the performance of an engine. Thus, you must maintain it and keep its condition well. Moreover, it would be best to fix it as soon as possible should it be necessary to do so. For this reason, you may wonder how you should do so and how much you need to prepare. Thus, you may ask:

How to fix spark plug thread, and what is the repair cost? If you plan on rethreading your spark plug, you need to prepare at least $1000 if you want the best service. Or, you can also do it yourself by purchasing some tools which will cost way cheaper. First, however, you need to make sure you know what you’re doing before you proceed.

Due to frequent usage over time, the spark plug wears down as well. Thus, it can generate holes in its thread, which needs repairs. If left unchecked, these damages can invite more issues to your engine’s performance. Thus, it’s necessary to deal with these things soon to avoid more expensive and complicated repairs in the future.

This article will teach you all the things you need to know about repairing a spark plug thread and the possible costs it will require you. This way, you can be prepared, and you’ll know how to deal with it when it happens to your engine.

Without further ado, let’s get into it!

How to Fix Spark Plug Thread and What Is the Repair Cost

How Much Does It Cost to Rethread a Spark Plug Hole?

As I mentioned earlier, the best way to rethread a spark plug hole is to bring it to a professional and have it repaired. However, if your spark plug needs a proper repair (if it was a stripped one with crossed and pulled-out threads), it can cost a lot.

If such a thing happens, the mechanic needs to remove the head from the engine. While it sounds pretty simple, it’s pretty complex and time-consuming.

Using a thread repair kit, you can quickly restore the threads. This version includes a bigger tsp and a steel thread substitute that fits into the tsp hole. 

If this is attempted without taking out the head, metal from cutting new threads for the thread replacements may reach the cylinder, causing irreversible problems.

In general, you should expect repair costs of as much as $1000 for such complex repairs. Now, if you know what you’re doing, you can always buy some tools and do it yourself.

Can You Rethread a Spark Plug?

Yes, you can rethread a spark plug using several tools. One of the typical repair approaches would be through inserting a Helicoil.

If you have a spark plug hole that needs rethreading, you can repair it by inserting a Helicoil. Another thing you can do is track the old threads. 

You can do it by getting a thread chase that suits your thread’s size. Then, track the old thread, tap the right size, wash it, and then your spark plugs will be ready to use again.

In general, it would be best to proceed with caution and make sure you understand spark plugs and how to go around them to avoid further problems from arising.

How Do You Fix Spark Plug Threads?

As I mentioned earlier, you can insert a Helicoil to fix spark plug holes or use a thread chaser. However, if the damage is a lot deeper, you may have to remove the cylinder head.

Here are a few simple procedures you can use when repairing a spark plug thread:

Basic repairs

The first step in repairing the spark plug hole is to purchase a thread repair kit or an insert kit and put it into the spark plug hole. Thread repair kits are widely available at car stores and may also be purchased on Amazon. 

You can find things such as thin wall plates, a chisel, a tap, and installation gear in these packages. You’ll need the following items to repair your spark plug hole.

Spark plug hole repairs

Remove the spark plug first to reveal the damaged threads in the hole. Then, use the pressure tool to wash the affected threads. 

Lube the thread to prevent aluminum shards and to capture all particles while re-tapping the threads. Lubricating is required because aluminum shards can cause damage if they get inside the engine.

Now, insert the tap into the hole and spin it gently and gently to begin cutting the replacement threads. Again, you don’t want to destroy anything within the hole, so turn it carefully and gently.

Use the old broken threads as a reference when chopping new threads to ensure proper alignment when reattaching the threads. Cut larger threads and secure the tap in the remnants of your previous spark plug threads as you slide the tip into the spark plug pit.

Secure the new threads in a way that they are parallel to the old and damaged ones. Further, you must place the new threads over the old and remaining good ones.

After threading until the bottom, remove the tap in the same position as the previous threads.

Finishing steps

You must screw the thread insert onto the installation mandrel and then tightened it. Now, put the new and replacement threads into the spark plug hole with the installation mandrel that came with the recoil kit. 

Afterward, clean the installation tool after removing it from the hole. Last but not least, return the spark plug to its original place.

What Is the Best Spark Plug Thread Repair Kit?

If you’re looking for the best repair kits for your spark plug thread needs, you may find these five kits reliable. Take a look at each one to have an idea of which one suits your needs best.

Helicoil 5521-4 1/4-20 Inch Coarse Thread Repair Kit

This product is a 1/4-20mm thread repair kit. It’s an easy-to-use kit with 12 inserts accompanied by a whole set of manuals for use.

The kit also comes with a Helicoil tap and installation tool. It is made from high-quality material that makes it a reliable tool for your repair needs. Like the other Helicoil, it comes in carded packing and is usually used for repairing tapped holes.

Helicoil 5521-5 5/16-18 Inch Coarse Thread Repair Kit 

This Helicoil has a size of 5/16-18 inches. It’s a straightforward repair kit to use and is from China. 

The kit consists of 12 inserts, a complete set of manuals, a Helicoil tap, and an installation tool. With such contents, you can repair tapped holes, and it’s reliable with its high-quality materials. In addition, the kit comes in a carded package, making it straightforward to use for every user.

OEMTOOLS 25649 14mm Cylinder Head Re-threaded Kit

This product is a 14-millimeter cylinder head re-threaded kit, and you can use it to repair a spark plug. With this kit, you won’t need anything else, and any user can do it. The only con is that it’s only for the users with spark plugs with aluminum heads.

The repair kit boats of its quality materials that are made to last for an extended period. It consists of several inserts to accommodate your needs for your spark plug. It includes:

  • 3/8 insert
  • 7/16 insert
  • 1/2 insert 
  • 3/4 insert
  • Combination tap or reamer

One thing to note is that it has a one-year warranty, so you won’t have to worry if anything happens to your product. It’s also easy to store and would safely go to your drawers without issues.

CalVan Tools 38900 Two Valve Ford Triton Tool Kit

The manufacturer of this product designed it to help repair two-valve modular cylinder heads from ford engines. It’s of suitable quality materials that boast a fool-proof repair system. Thus, it allows for cost-effect and quick repairs for your spark plug thread.

You can also use this item to repair damaged heads due to blown-out spark plugs. Since the inserts included are oversized, they can replace the previously broken inserts. In addition, since it includes six inserts, you can replace them several times, saving you money in the long run.

ABN Spark Plug Thread Repair Kit

This product is a time-saver kit in the sense that it gives you the feature of cutting threads to fix a stripped spark plug hole. It also helps repair configurations of your spark plug but is only applicable to the plugs made with aluminum.

It’s also an easy-to-use product suitable for everyone since you can follow the instructions given.

The kit comes in a 14mm reamer with 12 points. It has an overall length of 2.5 inches, and you can use it with a 3/8-inch wrench or drive ratchet.

The whole kit contains a tapping reamer together with four various inserts of different depths for your use.

Where Can You Get Your Spark Plug Thread Repaired?

Now, if you’re not familiar with repairing your spark plug thread on your own, an expert’s help would always be the best bet.

In general, a spark plug thread repair is something you can access in typical automotive centers and repair areas.

Thus, you can take your vehicle for a repair and say that you’ll need help with the spark plug thread.

The mechanic would examine your spark plug and see which repair method would be best for your case.

Of course, the cost of such would depend on the level of damage and the needed repairs. Also, it will be more expensive than repairing yourself. 

Still, it’s one way to make sure that your engine works find and avoids further issues due to unresolved spark plug threads.


In a nutshell, fixing a spark plug thread can cost more or less, depending on how you will deal. If you know how to repair it, you can do so with costs amounting to only a hundred dollars or more for the tools you need. However, it can cost thousands of dollars to take it to a mechanic for the best service.

In a nutshell, spark plug thread repair is not very simple, but you can easily do it yourself following these procedures. Note that while this may appear to be a primary and straightforward task, you should go to your technician and have him complete the task for you if you have no prior expertise. 

A mechanic may repair a spark plug hole professionally and quickly with the aid of experts. First, you must ensure that your engine and the plugs are in good working order. Then, you may rethread your plugs by following these easy steps.

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Image credits – Canva

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My name is Hank, and I've been in the automotive industry for 27 years. I've been working in my own auto repair shop for the last 13 years, and now I want to help you here, on my blog. Let me know if you have any questions. Read more