FAA Powerplant Written Practice Test

During visual inspection while overhauling an engine, the piston heads were depressed. This is a sign that?

1. Oil contamination occurred

2. Engine overheating occurred

3. Detonation had occurred

4. Piston rings are worn

The correct answer is: Detonation had occurred

Depressed piston heads are indicative of detonation events that have occurred in the engine’s combustion chamber. Detonation, also known as pre-ignition, occurs when the air-fuel mixture ignites prematurely due to excessive pressure or increased temperatures. This premature ignition can produce a significant shock wave within the combustion chamber, leading to deformation of the piston head. The structural integrity of the piston is compromised under such conditions, showcasing visible signs such as depression or pitting on the surface. Recognizing this sign is crucial for mechanics as it affects engine performance and requires immediate attention to prevent further engine damage. Understanding these symptoms helps technicians identify underlying issues related to combustion timing and fuel quality, ensuring longevity and reliability for the engine.