How To Rethread A Spark Plug Hole: 3 Effective Steps

When it comes to cars, the spark plug hole gets stripped to threads, which is common. It happens when there is an attachment between the spark plug hole and the cylinder top for an extended time. 

The aluminum threads get out off when it is not changed for a long time. Everything expires after a certain period, and when it comes to a car spark plug hole, then the deterioration of the spark plug’s health starts soon.

To fix the issue, you need to rethread the plug hole, ensuring that you have a professional to do it. If you have never done the process of rethreading an engine, then an expert is essentially required. 

Things Need To Rethread A Spark Plug Hole:

Few ways can help in rethreading a spark plug hole. 


One of the common and effective ways of rethreading is by inserting a Heli coil. Another essential tool, the thread chaser, can keep track of old threads while purchasing. It can determine the size correctly so that you can wash it. 


For rethreading fast, you can also use the following materials such as: 

  • Steel
  • Aluminum
  • Cast iron

Time required

You must ensure that the threads aren’t extensively damaged. In case the thread is poorly damaged, you need to take off the head of the cylinder.

Thread repairing is not an easy process, so a correct repair of the thread can take a lot of time. 

How To Rethread A Spark Plug Hole – 3 Effortless Steps

Rethreading is not for beginners. Professionals can handle it easily, and thus following certain steps can provide you with a better result and complete the task. The steps are:

Step 1 – Starting from basics

Even before you start repairing the spark plug, the first thing is to purchase an insert kit or thread kit. You need to simply install the kit in the plug hole. 

You can find the repair kits of thread in the local auto store or local tool store, other than that you can look for them online too. 

The thread kits come in the form of a package which includes:

  • Narrow wall thrust 
  • A drilling machine
  • A pipe 
  • ½ long piece stainless steel wire
  • Specific tool required for installation

The package also has the manual and details of every component included in it. So for you, it can certainly be easy to properly apply the kit. 

Step 2 – The core process

For seeing the empty threads inside the hole, you need to start removing the spark plug. Firstly with the assistance of a tapping tool, you need to clean all the damaged threads.

To get the shavings during the re-tapping of threads and avoid aluminum chips, you need to use lube in the tap. 

It is crucial to grease the tap. Greasing helps the aluminum chips to get blocked. Because once if the aluminum scrap gets in the interior part of the engine, it can damage and harm the engine. 

Afterward, you need to attach the pipe to the hallowed part, and for chopping the newt tenors, you need to rotate it steadily and fluidly. 

You don’t desire to crack or cause minor damage to anything in the interior part of the ravine, so it is important to remain careful when you cut the threads. 

For better performance, you can use the matured vandalized tenors as an usher so that you can correctly place the new threads in the proper positioning format as you need to place the tenors in the previous place. 

Ensure that you pierce big-sized tenors and keep the tap as tighten as possible in the leftover old threads of the spark plug. When you are threading, tap into the hole of the new spark plug. 

You need to ensure that the latest tenors are kept in parallel form to the matured blemished tenors. You must keep the threads correctly, so you need to keep the old thread over the new one. 

You can also place some good thread over that and ensure that the plug fits into the hallowed part properly.

Once you are completed threading up to the bottom, you can remove the tap out. This is the same position where the matured tenors are kept in the middle of the hallowed part. 

Step 3 – Final touch

You need to complete the insertion of the mandrel part in the final step by inserting the thread and screwing it. Make sure you tighten the screw properly so that the thread does not loosen up.

Now further with the blench equipment, you will need to install the mandrel. Also, you need to place the new tenors, which are a bit oversized, in the plug hole. 

Make sure that you remove the insertion apparatus from the hallowed part and sterilize it correctly. 

Finally, put the plug of spark backward to its original place. And you are good to go with the rethreading. The tedious task is finally complete. 

You may find them a little bit hard from the steps as rethreading a plug of spark is not straightforward. 

Although maintaining the steps correctly can provide you with a better result, you can surely do the rethreading of a plughole of spark by yourself. 

Different Parts Of The Plug


The primary part of the insulator is made from standard sintered alumina. It is a very tough ceramic-type material that has a high amount of dielectric strength. 

For improving the resistance in the surface, glazing is done. The primary function is to provide electrical insulation and mechanical support to the centralized electrode. 


The top part of the spark plug connected to the ignition system contains a terminal. The precise construction of a terminal depends on the use of the spark plug. 

Most cars have snap terminals, and some have eyelet connectors that are fastened onto the plug placed under a nut.

Insulator tip

The combusted shell is similar to sintered aluminum oxide for the modern sparks plug. The uppermost part is barely unglazed containing ceramic coating.

Sintered aluminum sapphire is considered a superior metal as it has very good relativity to conduct thermal temperatures. 

Other than that, it allows low construction costs for a single piece and provides elevated automated reliability. 


The functioning of the rib tends to increase the length between the grounded metal case and the high voltage terminal of the spark plug.

It also helps to improve the electrical insulation, and so no leaking occurs for electrical energy. Although some spark plugs are not provided ribs, they are manufactured without them. 


Seals are the prime essentials for preventing and stopping leakage from the combusted shell. When the engine of the combusted shell is installed, the spark plug seals it off. 

The seals of present days are created of constricted metal powder or glass. Before in the early days, seals were made of brazing. Seals are divided into two categories, and they are:

  • Internal seal
  • External seal

The work of an external seal is to protect the engine from the water. 

Metal shell

The spark plug’s metal shell is crucial as it tightens the plug by applying torque. It works as the medium of removing the heat from the insulator and passing it towards the cylinder head. 

Moreover, it also acts as a ground for sparks through the central electrode to the side electrode. 

Centralized electrode

An internal wire is commonly a ceramic series, and it connects the central electrode to the terminal end. It helps to reduce the emission of the RF noise when the sparking takes place. 

Due to the lack of this element, there will create insufficient interference with sensitive equipment and radios. 

The metals used in the formation of the centralized electrode are nickel-iron, copper, chromium, and other standard metals. 

Side electrode

The side electrode, also known as the ground strap, is made from high pressured nickel steel and is hot forged or welded to the side of the metal shell. When it is projected on the nose plug, the hotness of the side electrodes is found. 

For increasing conduction, some designs have included copper core to the electrode. Although multiple side electrodes may be used still there does not occur any overlapping in the central electrode. 

What are spark plugs used for?

There are various purposes for a spark plug, and it can be used in many places. It is used in direct ignition of Saab when they are not fired. 

Also, one of the primary works of the spark plug is to measure the ionization of the cylinders.

When it comes to measuring the ionic current, the spark plug has replaced the typical cam phase sensor. Also, the misfire measurement function and knock sensor are replaced by a spark plug. 

The other spark plug application is seen in furnaces where it is ignited in the combustion mixture of fuel or air. So that is why due to the application in these places, sometimes spark plug is referred to as flame igniters. 

Construction of a spark plug

The composition of a spark plug consists of a shell, an insulator, and a centralized conductor. 

It needs to pass from the wall of the combustion chamber and seal up the chamber of combustion against a high amount of pressure and temperature is made it that way. 

If it was not made skeptical, it would quickly deteriorate if used for a long and extended period.

There are various spark plug sizes, and they come in multiple forms, too, such as sealing type, spark gap, and thread or nut out. 

The standard threaded nut size is 10mm, 14mm, 18mm, respectively. The sizes are the same everywhere. 

Finals thoughts

The best way to solve it is by letting your mechanic do the work for you. With the help of experts, you can efficiently and professionally rethread a spark plug hole. 

One thing that you need to ensure is that your engine remains healthy and so the plugs too. It is vital that you don’t mislead by other information and don’t carry out different operations. You need to ensure your safety too.

Every thread is important, so you need to operate correctly with each thread and place them correctly in the proper manner. 

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