Spark Plugs for Outboard Motors
The ignition voltage generated by the spark coil and timer (ignition contact - today an electronic ignition system) is transmitted to the spark plugs via the spark plug cables. There, the ignition spark generated by the ignition voltage jumps between a ceramic-insulated center electrode and an earth electrode fixed to the mounting thread, thus starting the combustion process. The spark plug should quickly reach its self-cleaning temperature between 360 and 850°C. Self-cleaning prevents a short circuit or a shorter spark gap between the electrodes by burning off combustion residues. The insulator nose surrounding the centre electrode determines the heat value of a spark plug by its length. With a short insulator nose, heat can be quickly transferred to the cooled cylinder head via the thread. This is referred to as a "cold" plug with a high heat value. This is used for highly stressed engines. The heat values of spark plugs must be adapted to the respective engine. If the spark plug is too "cold", the above malfunction may occur. If, on the other hand, the plug is too "warm", the electrodes will burn too quickly. Spark plugs must be replaced regularly due to electrode wear.