Installation / Failure Analysis
Recommended Torque and Tightening Angle
1. Use the correct wrench for the hex on the plug, and be careful not to damage the insulator.
2. When changing, make sure that no foreign substance falls into the combustion chamber.
3. When putting the plugs in, make sure that all cylinders are clean.
4. Make sure the plugs are vertical, then tighten them by hand until they cannot be tightened any further (A+B).
5. Then, use a spark plug wrench to tighten them accurately according to the recommended torque specification (C+D).
Installation Warning
- With the use of oil or lubricant, the tightening torque must be 30 Nm for Cast Iron heads and 22.5 Nm for Aluminium heads for M18 thread
- With the use of oil or lubricant, the tightening torque must be 20 Nm for Cast Iron heads and 17.5 Nm for Aluminium heads for M14 thread
Failure Analysis
An effective way of diagnosing the engine’s operating condition is to check if the spark plugs look abnormal. If all cylinders are operating normally then the spark plug appearance is light grey, there are tanned deposits and there is a slight electrode erosion.
Possible Cause of Shorter Plug Life
- Non high quality gas fuel such as bio-gas, landfill gas will accelerate wear of electrodes
- Increase in energy of ignition coil accelerating wear of electrodes
- Deterioration of ignition coil causing a decrease in ignition voltage being supplied to the spark plug
- Deterioration of plug boot decreasing flash-over resistance