Spark Plug

- What is the heat rating of a spark plug?

A spark plug must dissipate the heat produced by the combustion gases. The heat rating is a measure of the amount of heat dissipation.

The heat rating is expressed as a number.

A low number, Hot Type (for low speeds). A High Number, Cold type (for high speeds)

* It has a larger surface exposed to the combustion gases.
* It dissipates heat slowly.
* It has a smaller surface exposed to combustion gases.
* It dissipates heat quickly.
* Its firing end heats up quickly.
* Its firing end does not heat up quickly.



MEMO
It is essential to use a spark plug that fits a specific engine and its conditions of use.

1. When the heat rating is too high
The spark plug temperature remains too low, and causes deposits to build up on the firing end; the deposits offer an electrical leakage path that gives rise to loss of sparks.

2. When the heat rating is too low,
The spark plug temperature rises too high and induces abnormal combustion (pre-ignition); this leads to melting of the spark plug electrodes as well as piston seizure and erosion.

2. Why is the firing end appearance of a spark plug important?

Because the Firing end appearance reflects the suitability of the spark plug as well as the condition of the engine.

There are three basic criteria: good, fouled, and overheated. The firing end appearance also depends on the spark plug tip temperature.



MEMO
The boarder-line between the fouling and optimum operating regions
(450 degrees celcius) is called the spark plug self-cleaning temperature.
It is at this temperature that the deposits accumulated are burnt off.

* Burning-off of accumulated deposits
* Self-cleaning temperature (450ºC)

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