Skip to main content

Spark plugs are a crucial part of a gas-fueled combustion engine. That’s why it’s recommendable to have a regular check on them during routine vehicle maintenance. It’s easy to identify the signs of a faulty spark plug and whether it needs replacing if you clearly understand its parts. Here’s a thorough look at the components of a spark plug and how the auto part works.  

How a spark plug work 

A factory worker testing KLG spark plugs in the United Kingdom (U.K.) in 1939
A factory worker testing KLG spark plugs | Daily Herald Archive/SSPL/Getty Images

As defined by Christian Brothers Automotive, a gas-fueled engine works by turning gasoline into actual movement, a process known as internal combustion. A spark plug is vital for this process. Internal combustion starts when a mixture of air and fuel fills the engine cylinders. When the engine piston moves up, it compresses the air-fuel mixture by creating a small space, resulting in more potential energy. 

Jalopytalk notes that the spark plug creates a spark that ignites the mixture, creating an explosion that pushes back the piston, creating the power to move the vehicle. The piston is pushed back once the exhaust clears out, starting the process over again. This cycle is what keeps the vehicle moving. 

Gas-fueled vehicles vary according to the number of cylinders their engines have. A four-cylinder engine would have four spark plugs, six for a six-cylinder engine, and so on. However, a Chrysler Hemi engine has two spark plugs per cylinder. 

Components of a spark plug 

A spark plug has eight major parts, according to Champion Auto Parts. Each of these parts aids in powering a vehicle. Here’s a list of these parts and a brief description of their use:

  • Terminal: The terminal attaches the spark plug to a high-voltage current from the ignition system. In some vehicles, the terminal contains a nut that supports the cord. 
  • Insulator: This part insulates the terminal, central shaft, and center electrode from the housing. It prevents the escape of high voltage from the plug’s electrodes. 
  • Metal body: This threaded steel shell transfers heat from the plug to the cylinder head. 
  • Central electrode: This is a nick-based alloy attached to a copper core. High voltage from secondary winding is applied to it through the distributor. 
  • Ground or side electrode: This is a nickel-based alloy, titanium-reinforced, or iridium welder to the metallic body of the spark plug. It creates a spark path on the central electrode.  
  • Plating: The shell is usually plated to increase durability and ensure corrosion resistance. Its polygon allows a spanner to plug and remove it from the cylinder head. 
  • Gasket: The gasket ensures that the spark plug housing fits perfectly into the engine. Vehicle owners must follow the recommended procedure to secure a suitable locking margin. 
  • Ribs: These parts provide additional protection against spark arcs and secondary voltages. 

Importance of understanding the parts of a spark plug 

Understanding the parts of a spark plug helps you know how it works, determine whether it’s faulty, and safely change it. However, there are obvious signs of a faulty spark plug, including having a rough idle, trouble starting, misfiring, and engine surging. These signs mostly indicate that you should replace the spark plug. 

Now that you understand how various parts of a spark plug work, it’s easier to change a faulty one. Changing your spark plug saves you time and money. AutoZone recommends the following steps to change a spark plug:

  • Maintain safety by parking your car on a flat, dry surface, and ensure the engine has cooled down
  • Remove the spark plug wire
  • Remove the coil on the plug
  • Unscrew the plug
  • Put in your new plug
  • Reinstall the spark plug and ignition coil
  • Start the engine to check whether the spark plug is functional

If you find it challenging to change your plug, it’s best to seek help from an experienced mechanic.


I Accidentally Killed My First Car by Changing the Spark Plugs