How should aircraft engine spark plugs be installed?

The proper installation of aircraft engine spark plugs requires that they be installed finger tight initially and then tightened to the specific torque value recommended by the engine manufacturer. This ensures that the spark plugs are securely fastened while avoiding damage to the engine components.

Using finger tightness allows for initial alignment without cross-threading and ensures that the spark plug is seated properly. Following this, applying a torque wrench to tighten the plug to the manufacturer's specified torque prevents over-tightening, which could lead to stripping the threads or damaging the spark plug as well as the engine head.

This method balances the need for a secure connection with the potential for thermal expansion and contraction that occurs during engine operation, which can affect how tightly the spark plugs are held in place. Additionally, it supports maintenance practices that promote consistent performance and reliability of the engine's ignition system.