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Automotive glossary: What is a Spark plug or Sparking plug?

Spark plug
Definition of Spark plug: For igniting the gas mixture, which drives the engine by exploding, petrol engines need a device to produce a spark. As this device inevitably outwears by the sparking, it can not be integrated into the engine, but has to be replaceable as a wear part. This function is performed by the spark plug. The spark leaps between one or more "earth electrodes", connected to the thread, and the central electrode, visible in the inside. By the high temperature in the combustion chamber of the cylinder, the spark plug cleans itself from the accruing combustion residues. It is important, to insert a spark plug with the correct heat rating. It can be learned from the operation manual. Also, with traditional spark plugs, the electrode gap has to be adjusted according to the vehicles reference setting with a gauge. When screwing in, make sure not to turn in the thread canted, as this will result in vast repair works. Beside this, the spark plug must not be fastened too firmly, as the cylinder head might be damaged by material extension through the heat build-up. The color of the electrode of a used spark should be fawn, light gray to white means a to lean mixture, black resp. sooted a too rich mixture.

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