How to Guides

Spark Plugs

Zaki Moulvi posted this on Jun 16, 2014

Like the name implies, a spark plug is a simple device that is screwed onto the cylinder head, enabling it to deliver the spark needed to ignite the air and fuel mixture inside of the combustion chamber.

Spark Plugs History

The first internal combustion piston engine was created in 1860 by Etienne Lenoir, who is credited as being the first to use an electric spark plug.  By 1902 the first commercially viable high-voltage ignition device was created, making the spark ignition engine possible.  Spark plugs have undergone many improvements in the last 100 years, but the basic function still remains the same.  Their sole responsibility is to provide the spark necessary to ignite the air fuel mixture inside of the combustion chamber that will allow enough power to be generated to get your car moving.

Spark Plug Parts

Making up a spark plug is a shell, insulator and the central conductor.  Since spark plugs are passing through the wall of the combustion and sealing it, they must be durable to high pressure and temperature.  The main components in the spark plug construction are:

  • The terminal, which connects the spark plug to the ignition system.  This allows the electricity needed for the spark plug to ignite.
  • The insulator is the hard ceramic casing covering the spark plug. It is in place to provide mechanical support as well as supply an insulation to the central electrode.
  • The insulator tip is the part that is protruding into the combustion chamber.  It is designed to function in temperatures well over a thousand degrees Fahrenheit.
  • Seals are necessary to ensure that the combustion chamber remains free from any leakage as a result of the spark plugs presence.
  • The metal case helps to remove unnecessary heat from the insulator and pass it to the cylinder head. 
  • A central electrode, which is connected to the terminal.  It is here that the spark is created.
  • The side electrode above the central electrode.
  • The spark plug gap is the space between the tip of the central electrode and the top of the terminal.

Cold Plugs

For a high compression engine giving off a high amount of horsepower, cold plugs work best.  They contain less insulation allowing them to transfer a greater amount of heat away from the combustion chamber to the outside of the engine.  It is important to know if your engine uses this type of spark plug.  In some vehicles, if not enough heat is dispersed permanent engine damage could occur.

Hot Plugs

Most modern vehicles use the heavier insulated hot plugs.  The plugs temperature remains high, allowing carbon deposits to be burnt off.  This increases the life span of your spark plugs.

How Spark Plugs Work

Using a series of wires, each spark plug is connected to the ignition coil.  There is one spark plug for each cylinder and piston combination in a vehicle.  As electrons flow from the coil a difference in voltage occurs between the central electrode and the ground electrode.  As that voltage continues to rise in the central electrode the structure of the air fuel mixture changes, and the gases become ionized.  This allows electrons to flow across the gap, create a spark and ignite the mixture. 

Changing Spark Plugs

Basic maintenance of a vehicle includes changing the spark plugs. Worn or dirty plugs will have an impact on the cars performance and can cause anything from a delayed start to engine stalling.  Bad plugs will also cause you to burn gas faster than normal.

When buying new spark plugs be sure that they are compatible with your vehicle.  If you car requires hot plugs for example than this is the type you need to replace yours with.  Consult your owner’s manual for clarification.  You will also need to purchase a spark plug socket for removal and installation.

Once you have located the spark plugs you will need to separate them from the spark plug wires.  Then you can place the spark plug socket with ratchet wrench over the end of the plug and remove it.  If it seems to be stuck apply some lubricant to the seal before trying again.  A bigger problem than a worn spark plug is half of a broken one falling down into the combustion chamber.

Replacing the plug is simply screwing the new one into the hole with the same ratchet and socket.  Adjust the torque according to your owner’s manual directions.  One in place you can reattach the wire assembly, which can also be easily replaced if it looks worn.  With each plug removal you are exposing the inside of your engine block to dirt and particles.  For this reason it is best to attempt this job one plug at a time.

Troubleshooting Spark Plugs

 You can tell a lot about what is going on by how old spark plugs look when you remove them.  A dirty plug is fine, but if it is glossy then the plug has been overheating.  A white tip indicates that the spark plugs you are using are too hot for your engine and needs to be replaced with one that has less insulation.

What you are looking for is oil on the spark plugs.  If the plug appears greasy than oil is entering the combustion chamber and you have a more serious problem to contend with.

Spark plug technology is one of the few car innovations that relatively resembles the original idea.  With changes being made only in their level of efficiency it is easy to see that the original design was a very good one, considering the time in which it was invented.

Categories: Autowiki Car Systems