How To Helicoil Damaged Spark Plug Threads


As you change the spark plugs over the years, the aluminum threads that are supposed to hold the spark plugs in place get worn. This happens because the spark plugs have metal heads and as you tighten them, it starts to pull the threads out of the aluminum heads.

How To Helicoil Damaged Spark Plug Threads

When the spark plug threads are damaged, the spark plugs are no longer secured and will wobble when you turn on the engine. The spark plugs have to be secured in one place so that the spark is delivered into the combustion chamber. Here is How To Helicoil Damaged Spark Plug Threads:

1. Remove the spark plug wiring

How To Helicoil Damaged Spark Plug Threads

To gain access to the spark plugs, you will have to remove the valve cover, spark plug wiring, any additional wiring that might be in your way, and finally the spark plugs.

What exactly you will need to remove in order to reach the spark plugs will depend on your engine. Newer engines will have plastic covers, and older engines might not have.

2. Make sure the valves are closed

How To Helicoil Damaged Spark Plug Threads

Before you start repairing the threads on the spark plugs, you must make sure that the valves inside the cylinder are closed. This is super important because later on when you start working on the damaged spark plug threads, you’ll get metal shavings to fall down into the cylinder.

The valves open and close when the crankshaft rotates. Each valve is opened and closed at the right time. You will have to rotate the drive chain until the valves are closed. This part of the process can be challenging but trust me, you don’t want metal shavings to fall in your cylinder.

3. Access the damage

How To Helicoil Damaged Spark Plug Threads

In this step, you have an exposed spark plug threads and you need to access the damage. Remove all the spark plugs that you suspect might have a damaged thread and do an assessment of the overall damage.

I usually start by vacuuming the spark plug hole because there is metal scrape all over the hole because of the broken threads. Then, I grab a flashlight and do a quick assessment and I make sure that the valves are closed and no metal scraping will fall into the cylinder and cause a ton of other problems.

4. Oversize the spark plug hole

The Helicoil spark plug repair kit (see the price on amazon.com) will come with a sleeve that you will have to put inside the spark plug hole. You will have to drill the spark plug hole big enough so that the sleeve from the repair kit can fit in.

5. Put grease on the drill bit

How To Helicoil Damaged Spark Plug Threads

This is a pro tip that will make your life easier. Before you start drilling, put some grease on the drill bit. The grease on the drill bit will hold all the metal shavings that will come off as you start drilling. Each metal shave that you caught on the grease is a metal shave that will not fall down into the cylinder.

To choose the correct drill bit to drill the spark plug hole, get the size of the wire that your car uses and get a slightly larger drill bit. Usually, #80 or #70 drill bits work just fine.

6. Start drilling the spark plug hole

It is key that you start drilling the spark plug hole with ease. Do not start reaming it out because you are going to have problems later on. Drill little by little. You will notice that the grease on the drill is catching a lot of metal scraping. You can go ahead and reapply more grease.

7. Clean the spark plug hole

The grease on the drill bit will catch a lot of metal scraping. But, some of them will probably still be in the hole. You need to clean the spark plug hole without allowing the metal scraping to fall down in the cylinder. Grab a screwdriver and carefully remove any leftover metal scrapings.

8. Apply anti-seize on the new thread

Before you start thread cutting, you need to apply some anti-seize on the new thread. The new thread is metal and the engine block is made out of aluminum. It will seize up if you are not careful. Another reason why you need to put anti-seize on the new thread is that it will catch all the new metal scraping.

9. Insert the new thread in the spark plug hole

How To Helicoil Damaged Spark Plug Threads

Insert the new thread from the Helicoil repair kit into the spark plug hole and gently hit it with a hammer until it is secured. Once the new thread is secured, get a wrench and start tapping.

The tapping process should not be forced and you have to be careful not to overdo it and damage the cylinder. Go slowly and you will feel when there is no more room to go. At this point, you should have a new thread made in the spark plug hole.

10. Clean the spark plug hole

As soon as you are done installing the new insert in the spark plug hole, blow out the hole and make sure that all metal scraping residue is out. Then, you will need to remove all of the anti-seize.

The reason why you need to clean all of the anti-seize is that you won’t want to mix it with the Loctite that you are going to put in there next. Loctite will make sure that the new insert that will install in the next step, stays there.

11. Select and install the correct insert from the repair kit

You will select the correct size insert by screwing it on the spark plugs that you use. Once you find the correct size, apply Loctite to the insert. The reason why you need to apply Loctite on the new insert is that you want it to stay in place when you remove the spark plug.

Place the new insert into the spark plug hole and use a spark plug to push it all the way down. Use a spark plug wrench to tighten the spark plug. You can check if you are all the way down by removing the spark plug. But you will feel it when the tapping will become hard. Once you reach the bottom, leave the spark plug there for 10 minutes.

12. Reinstall the spark plug wiring and start the car

Once 10 minutes have passed and the spark plug insert has settled down, it’s time to reinstall the spark plug wiring, valve cover, and any other wiring that you had to remove in order to gain access to the spark plugs.

At this point, you should have new spark plug threads and your vehicle should start running properly.

Related Questions

Do Helicoils work in aluminum? Yes, you can install Helicoils in an aluminum engine block as long as you follow the instructions and perform the installation the correct way. Since the Helicoil is metal and the engine block is aluminum, you will have to use anti-seize to ensure no seizing will occur when you are installing the new thread.

How do I know what size Helicoil I need? You can determine the correct Helicoil size you need by measuring the thread major diameter of the mating bolt and measuring the thread spacing or pitch using a thread pitch gauge. Look for a good fit between the gauge and the threads of the bolt.

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