FAA Powerplant Written Practice Test

Where on the cylinder walls of a normally operating engine will the greatest amount of wear occur?

1. At the bottom of the cylinder

2. In the middle of the cylinder

3. Near the top of the cylinder

4. Evenly around the cylinder

The correct answer is: Near the top of the cylinder

In a normally operating engine, the greatest amount of wear on the cylinder walls typically occurs near the top of the cylinder. This is primarily due to the operation of the engine, where the piston reaches the top dead center (TDC) position during its compression stroke. At this point, the combustion process generates high pressures and temperatures, leading to increased friction and wear at the upper portion of the cylinder. Additionally, the upper part of the cylinder experiences more exposure to combustion gases and the resultant heat, which can cause thermal expansion and stress. The ring’s function—sealing the combustion chamber and controlling oil consumption—also contributes to wear patterns, as the rings make the most contact with the cylinder wall in this region. Over time, this repeated high-stress interaction leads to more pronounced wear near the top compared to other areas within the cylinder.