What Do Spark Plugs Do? (Function, Parts, Types)

Spark Plug on a motorcycle engine

Gasoline engines can’t live without spark plugs. As a result, conventional motorcycles want spark plugs in good condition for a good engine performance.

But what exactly does a spark plug do? A spark plug ignites the fuel mixture in gasoline engines by producing a high voltage electric spark. The spark produced is usually in the range of 15,000 to 20,000 volts.

Only after the spark plug ignites the fuel mixture, will the fuel burn in the engine to generate power. So, if the spark plug is bad or not working properly, the motorcycle might not run.

Having discussed briefly on spark plug use, let’s deep dive into its role, parts, and its types.

Role of spark plugs in an engine

A spark plug is a component used in gasoline engines to ignite the air-fuel mixture. The spark plugs ignite the fuel by producing a high voltage spark in the combustion chamber. The spark generated will ignite the gasoline mixture paving for the fuel combustion in the engine.

The spark produced will be in the range of 15,000-20,000 volts.

Once the spark plug ignites the air-fuel mixture in the engine, the fuel mixture burns to produce energy in the engine. This generated energy is what drives the motorcycle along with powering all the accessories in the vehicle.

Without a spark plug, the fuel mixture in the engine will not combust at all. Since there is no ignition, there will be no burning of fuel in the absence of the spark plug functioning.

As a result, if the spark plug is not functioning, the engine won’t generate power at all. No spark ignition. No fuel combustion. Hence, no power is generated by the engine. That’s why a spark plug is such an essential component for a motorcycle. The motorcycle will not run without the spark plugs.

If the spark plug is not working properly, be it because the spark plug has gone bad or is worn out, the motorcycle will not start at all.

Spark plug parts

Now that we have a good idea of the functions of a spark plug, let’s dig into spark plug parts and their roles in the plug functioning.

Spark Plug Diagram


The terminal connects the distributor cap which is part of the ignition system right to the central electrode. The voltage electricity is conducted by the terminal right to the central electrode.


The insulator insulates the terminal and the shaft that connects the terminal and the central electrode. This insulation is essential to arrest the flow of electricity away from the electrode. It also ensures the high volt is not lost while transmitting along the shaft.


Spark plugs usually have a steel shell to facilitate tightening and loosening of the plug. The shell also provides electrical ground for the ground electrode and also helps in heat transfer via the cylinder head.


The threads along with the shell ensure that the spark plug is fit tightly. They cover the insulator and provide support to them. The main function is of course to help in the installation of the spark plug.

Center Electrode and Ground Electrode

The center electrode is connected to the terminal through a central shaft. The high voltage electricity is passed from the terminal through the shaft to this center electrode. Usually, the electrode is made of copper alloy, platinum, or iridium depending on the spark plug type.

The ground electrode acts as the grounding for the high volt electricity in the spark plug. It is a fail-safe to avoid any electrical hazard in the spark plug since it carries away any excess electricity generated.

The center electrode tip carrying the high voltage generates the spark in the small gap between this electrode and the ground electrode. This spark is what ignites the fuel mixture in the engine.

Do all engines use spark plugs?

Spark plugs are only used in gasoline engines. Since motorcycles exclusively have gasoline engines, all motorcycle engines will have spark plugs.

Engine and Spark plug

Cars, on the other hand, use both gasoline engines and diesel engines depending on the make and the model. If a car is using gasoline engines, it definitely will have spark plugs.

But, if the car is running diesel engines, then there won’t be spark plugs in them.

Now, why don’t diesel engines have spark plugs? Diesel engines use compression ignition and hence have no need for spark plug ignition. When the piston compresses the diesel fuel mixture in the combustion chamber, the compression is enough for the fuel to ignite and burn.

That’s the reason why diesel engines have higher compression ratios. The compression ratio is measured as the volume of the combustion chamber when the piston is at its lowest point (BDC – Bottom dead center) to when the volume when the piston is at its highest point (TDC – Top dead center).

A diesel engine usually has a compression ratio of 22:1. On the other hand, a gasoline engine typically has a compression ratio of 8:1. As you can notice, a diesel engine has almost 3x higher compression than that of a gasoline engine.

Different types of spark plugs

Spark plugs are mainly classified based on the type of material used. There are three main types of spark plugs:

  • Copper spark plugs
  • Platinum spark plugs (single and double)
  • Iridium spark plugs

Copper spark plugs are cheap and easily accessible. They were the most widely used spark plugs by the OEMs until the last decade. They are still popular though. But, they wear out fast and have a low operating temperature.

Platinum spark plugs are improvements upon copper spark plugs. They have a better life span, better-operating temperatures, and do not wear out fast. But they come at a higher cost and slightly underwhelming performance.

Double platinum spark plugs are a variant of platinum spark plugs. They don’t have many usages in motorcycles. Still, if you are interested, here is a detailed post on double platinum spark plugs.

Iridium spark plugs are the best performance spark plugs in the market right now. They can withstand high temperatures, have a great lifespan, and do not wear out fast. The only downside is the high cost. Still, the advantages provided outweigh the premium price it demands.

While this is a brief overview of these different spark plugs, for more information, here is an in-depth post on the three types of spark plugs.

Related Questions

Can a motorcycle run without spark plugs?

All conventional motorcycles run on gasoline engines. And gasoline engines need spark plugs to keep running. If there are no spark plugs in gasoline engines, the engine won’t generate power at all.

And motorcycles running on gasoline engines (which most motorcycles do) will not run if the gasoline engine is not powering it up.

So, all conventional motorcycles won’t run without the spark plugs at all since they use gasoline engines.

How often should you change spark plugs?

The spark plugs in motorcycles should be replaced every 8000 miles to 10,000 miles of distance traveled. In addition, the spark plugs need to be inspected every time you take your motorcycle for servicing.

The spark plug change varies according to the type of the spark plug used as well. Copper spark plugs should definitely be changed every 8000 miles. Iridium spark plugs can be changed much later than that. And platinum spark plugs somewhere in between.