21 Facts About Spark plug

Function of a spark plug is to produce a spark at the required time to ignite the combustible mixture.

The Spark plug is connected to the high voltage generated by an ignition coil or magneto.

Spark plug is composed of a shell, insulator and the central conductor.

Top of the spark plug contains a terminal to connect to the ignition system.

Spark plug threads are cold rolled to prevent thermal cycle fatigue.

Similarly, a Spark plug that was hot enough to run smoothly in town could melt when called upon to cope with extended high speed running on motorways.

The answer to this problem, devised by the spark plug manufacturers, was to use a different material and design for the centre electrode that would be able to carry the heat of combustion away from the tip more effectively than a solid nickel alloy could.

The premise behind the polonium spark plug, as well as Alfred Matthew Hubbard's prototype radium plug that preceded it, was that the radiation would improve ionization of the fuel in the cylinder and thus allow the plug to fire more quickly and efficiently.

Spark plug gap gauge is a disc with a sloping edge, or with round wires of precise diameters, and is used to measure the gap.

Length of the threaded portion of the Spark plug should be closely matched to the thickness of the head.

However, the level of torque currently being produced by the engine will strongly influence spark plug operating temperature because the maximal temperature and pressure occur when the engine is operating near peak torque output.

Spark plug is said to be "hot" if it is a better heat insulator, keeping more heat in the tip of the spark plug.

Whether a spark plug is "hot" or "cold" is known as the heat range of the spark plug.

The heat range of a spark plug is typically specified as a number, with some manufacturers using ascending numbers for hotter plugs, and others doing the opposite – using ascending numbers for colder plugs.

Heat range of a spark plug is affected by the construction of the spark plug: the types of materials used, the length of insulator and the surface area of the plug exposed within the combustion chamber.

For normal use, the selection of a spark plug heat range is a balance between keeping the tip hot enough at idle to prevent fouling and cold enough at maximal power to prevent pre-ignition or engine knocking.

The heat range of a spark plug has only a minute effect on combustion chamber and overall engine temperature.

Spark plug's firing end will be affected by the internal environment of the combustion chamber.

For example, a sandblasted look to the tip of the spark plug means persistent, light detonation is occurring, often unheard.

Conversely if the Spark plug is too hot, the porcelain will be porous looking, almost like sugar.

Indexing is accomplished by marking the location of the gap on the outside of the Spark plug, installing it, and noting the direction in which the mark faces.