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- Spark plug -NGK BR ES- BR9ES - Solid Type
Spark plugs differ in the following things:
Thread diameter
The usual threads are M10, M12 and M14. Classic vehicles usually have an M14 thread. 4-strokes and modern 2-strokes with fuel injection use the smaller plugs with M10 or M12.
Thread length
The common thread lengths are 19mm (long thread) and 12.7mm (short thread).
Heat value
The heat value is decisive for the thermal fatigue strength of the spark plug as well as its self-cleaning effect. A distinction is therefore made between so-called cold and hot spark plugs.
A cold spark plug is for engines that develop a very high combustion chamber temperature, usually engines that have a lot of power in relation to their displacement. A hot plug, on the other hand, is used in lightly loaded production engines. This type of plug quickly reaches a high temperature, which means that the soot on the plug burns off easily.
The temperature resistance is achieved by differently designed insulators. A cold plug can give off a lot of temperature via the cylinder head, while a cold plug strongly inhibits exactly this. The heat rating has nothing to do with the strength or performance of a spark plug. A cold plug in a cold (weak) engine will oil or soot and can break without damaging the engine itself. A hot spark plug in a racing engine will burn up and damage it ,usually severely.
The heat value of a spark plug is not standardized. Each manufacturer has its own code here.
Electrode material
Copper, platinum, silver or even iridium are used here.
The most common is copper, followed by silver and platinum. Due to the high prices for the precious metals, the spark plugs are also correspondingly more expensive than their copper counterparts.
The material is ultimately of interest almost only for wear, only the extremely thin iridium electrodes (Ø=0.6mm) have a higher ignition voltage, the spread of the flame front in the combustion chamber is improved.
