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Browse our range of spark plugs for your British classic car. Check the condition of your spark plugs. Proper functioning of your spark plug ensures better performance of your car. We recommend replacing your spark plugs every 20,000km.

Anglo Parts distributes spark plugs from the Champion and NGK brands, 2 of the world leader specialising in the production of spark plugs with over 100 years of experience.

The spark plug serves to ignite the aspirated gas mixture in the cylinder by an electric spark just before the end of the compression stroke. At the right moment, when the piston of the respective cylinder is almost at the end of the compression stroke, a current of very high voltage is passed through the spark plug so that a spark skips between the central electrode and the earth electrode. The skipping spark ignites the combustible gas particles in the spark area, developing great heat and igniting the contents of the combustion chamber within a very short time due to the propagation of the flame front.

To ensure the spark plug functions properly, the following three points must be observed:

  • the electrode gap
  • the heat rating
  •  the general condition (colour of electrode and porcelain)

The electrode burns off slightly during use, which is why the electrode spacing should be checked regularly and, if possible, adjusted to the value specified by the manufacturer (e.g. 0.4 mm). Too large a distance leads to a higher ignition voltage at the expense of spark duration (time), or in the worst case one has no spark. Measuring the electrode gap is done with a feeler gauge.

To perform optimally, the temperature of the insulator nose should not exceed 850°C for long periods of time, nor should it be significantly lower than 530° C for long periods of time. If the temperature is too high, the gas mixture may be ignited by the glowing insulator before spark discharge occurs. If the temperature is too low, the self-cleaning temperature is not reached, resulting in strong soot formation which is electrically conductive, which can cause the spark plug to fail.

To ensure that the spark plug is adapted to the thermal conditions of the type of engine in which it is used, they are available with different heat ratings. The heat rating expresses the ability of a spark plug to absorb and dissipate heat. With a "cold" spark plug, the insulator part exposed to the heat of the combustion gases is relatively short, releasing heat quickly to the cylinder head. In the case of a "hot" spark plug, the insulator nose is longer, resulting in greater heat absorption.

As for the general condition of the spark plug, it should not be contaminated by carbon deposits or lead residue. A spark plug, used under normal conditions with the correct operating temperature, has a deposit that is light coloured or grey.

For diesel engines, spark plugs are not necessary, because here the fuel is injected at the right time into the suctioned highly compressed air above the pistons, making this gas mixture self-igniting. However, one does sometimes find a glow plug in a diesel engine. This is an electrical heating element that preheats the gas mixture in a cold diesel engine so that the gas mixture can reach its auto-ignition temperature.