Motorcycle News (UK) - - This Week -

Spark plugs only ful­fill one pur­pose in life – they de­liver en­ergy pro­duced by the coil to the com­bus­tion cham­ber in the shape of a spark. How­ever, when this is 40,000 volts at a tem­per­a­ture of over 500-de­grees, they have to be built out of strong stuff! A spark plug has a shell, which is the part you screw into the engine, and within this shell is the ce­ramic. The ce­ramic is the in­su­la­tor that keeps the high volt­age that is pass­ing through the cen­tre of the spark plug from earth­ing – if you have ever touched an un­cov­ered HT lead when the engine is run­ning you will know why this is nec­es­sary! In the cen­tre of the plug you have a ter­mi­nal, which is the bit you con­nect to the coil via the plug cap, then a re­sis­tor seal and a cen­tral elec­trode, which is con­nected to the tip - the bit that sparks. Fi­nally, you have the ground elec­trode, which the spark jumps to from the cen­tral elec­trode and earths the whole spark plug through the plug’s body and then the bike it­self. Both elec­trodes are made from nickel al­loy for strength and then plated in pre­cious me­tals such as irid­ium to in­crease life span and im­prove per­for­mance.

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