How To Helicoil Damaged Spark Plug Threads

As you replace spark plugs over time, the aluminum threads that secure them become worn. This occurs because spark plugs have metal heads and as you tighten them, it starts pulling threads out of their aluminum heads.

When your spark plug threads become damaged, they are no longer secure and may wobble when you start your engine. To ensure the proper delivery of sparks into the combustion chamber, here’s how to Helicoil damaged spark plug threads:

1. Remove the spark plug wiring

How To Helicoil Damaged Spark Plug Threads

To access your spark plugs, you will first have to remove the valve cover, any spark plug wiring that might be blocking access and finally the spark plugs themselves.

What you must remove to access your spark plugs depends on your engine. Newer engines typically feature plastic covers, while older models might not.

Is your engine oil due for a change? Visit our Car Fluid Guide Website to learn the importance of changing your oil on time, which type of engine oil is best for your vehicle, and much more.

2. Make sure the valves are closed

How To Helicoil Damaged Spark Plug Threads

Before you begin to repair the threads on spark plugs, make sure all valves inside the cylinder are closed. Otherwise, when working on damaged spark plugOpens in a new tab.

When the crankshaft rotates, valves open and close precisely at the right time. You must rotate your drive chain until all valves have been closed – this part can be difficult, but be sure not to let metal shavings enter your cylinder!

3. Access the damage

How To Helicoil Damaged Spark Plug Threads

In this step, you have exposed spark plug threads and must assess any damage. Remove all spark plugs that might have a damaged thread and assess the overall situation.

When I start vacuuming a spark plug hole, there is often metal scrape all over it due to broken threads. With a flashlight in hand, I quickly assess the situation and make sure all valves are closed so no metal shavings fall into the cylinder and cause other issues.

4. Oversize the spark plug hole

The Helicoil spark plug repair kit (see the price on amazon.comOpens in a new tab.

5. Put grease on the drill bit

How To Helicoil Damaged Spark Plug Threads

Here’s a pro tip that will make your life simpler: before beginning drilling, grease the drill bit with grease. This will catch all metal shavings that come off during drilling and ensure none fall into the cylinder.

To select the proper drill bit for drilling a spark plug hole, take into account the size of wire your car uses and opt for a slightly larger drill bit – usually #80 or #70.

6. Start drilling the spark plug hole

Drill the spark plug hole with confidence. Do not try to force it, as that could lead to issues later. Drill slowly and notice how the grease on your drill is catching a lot of metal scraping – this means you can go ahead and add more grease if needed.

7. Clean the spark plug hole

The grease on your drill bit should trap most metal scraping, but some may still remain inside. To clean out this spark plug hole without letting them fall back down into the cylinder, take a screwdriver and carefully scrape away any leftover metal shavings with it.

8. Apply anti-seize on the new thread

Before you begin thread cutting, be sure to apply anti-seize on the new thread. As metal joins aluminum in an engine block, without proper care the thread could seize up. Furthermore, anti-seize helps catch any metal scraping as you thread the needle in place.

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 kitOpens in a new tab.

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 plugOpens in a new tab.

It is essential to clean all anti-seize from your machine before applying Loctite, as mixing them will cause irreparable damage. Loctite will ensure that the new insert installed in the next step remains securely in place.

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

Once you select the correct insert size for your spark plugs, apply Loctite. It is essential that the new insert stays secure when taking out the spark plug.

Insert 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 it securely; you can check if you are all the way down by taking out the plug – tapping should become harder as you near the bottom. Leave the spark plug there for 10 minutes to cool.

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.

Vide Polowenski

General Mechanic with over 20 years of experience specializing in General mechanics, exhaust systems, fuel systems, and fuse-related problems.

Recent Posts