NGK -Torqueing Spark Plugs
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Most spark plugs failures can be traced back to incorrect tightening torque. If it is set too low, there is a risk of compression loss and plug overheating. It is also possible that the insulator or electrodes may also be damaged as a result of excess vibrations.
If the tightening torque is set too high, the spark plug metal shell will be over stressed and possibly yield. The shell can also expand or distort. Distortion causes the heat dissipation zones to be disrupted, overheating or melting of the electrodes or even engine damage can occur.
