For spark plugs:
Overtightening
Damage to the spark plug body: If the spark plug is overtightened, the metal shell of the spark plug may be deformed or the threads may be damaged, resulting in an inability to install correctly or the need to replace the spark plug.
Broken spark plug insulator: The insulator in the center of the spark plug may crack or be damaged due to excessive pressure, affecting the function of the spark plug.
Affected thermal value: The thermal value of the spark plug (its ability to dissipate heat) may be affected by improper installation. Overtightening may cause the spark plug to overheat, which may affect ignition performance and may even cause ignition failure.
Too loose
Gas leakage: If the spark plug is not tightened to the correct torque, it may cause a poor seal and gas leakage, resulting in power loss, reduced engine efficiency, and may even cause incomplete ignition or detonation.
Poor contact: If the spark plug is loose, the contact between the electrodes will be unstable, which may cause intermittent problems during ignition, causing the engine to shake or stall.
Increased carbon deposits: Due to incomplete ignition, incompletely burned fuel will deposit carbon on the spark plug, which may cause spark plug failure in the long run.
For the engine:
The impact of over-tight installation on the engine:
Cylinder block damage: If the spark plug is tightened too much, it may have an adverse effect on the cylinder block or threads of the engine, which may cause thread damage or screw hole deformation in the long run, making it impossible to reinstall a new spark plug.
Poor cooling: If the spark plug is over-tightened, it may reduce its contact area with the cylinder block, affect heat transfer, cause the spark plug to operate at too high a temperature, and even cause the engine to overheat.
The impact of over-loose installation on the engine:
Insufficient power: Loose spark plugs may cause abnormal ignition, resulting in the engine losing normal combustion efficiency, which is manifested as a decrease in power.
Engine shaking or flameout: Unstable ignition can cause the engine to shake during operation, and even flameout in some cases, especially when driving at low speed or idling.
Spark plug damage: A loose spark plug will be subjected to greater vibration, which may cause damage to the spark plug electrode or wear of other components, leading to premature failure of the spark plug.
