FAA Powerplant Written Practice Test

Which engine component is most likely to experience galling?

1. Crankshaft bearings

2. Piston rings

3. Ball bearing assembly

4. Connecting rods

The correct answer is: Ball bearing assembly

Galling is a type of wear process that occurs when two metal surfaces slide against each other under high load, resulting in material transfer and adhesion. This typically happens in applications where there is a high degree of friction and inadequate lubrication. Among the components listed, a ball bearing assembly is particularly susceptible to galling since it consists of rolling elements that can experience high contact pressures, especially if lubrication fails or is insufficient. In a ball bearing assembly, the steel balls are in contact with the inner and outer races. If there is inadequate lubrication, or if particles or contaminants are present, galling can occur, leading to abrasive wear and potential failure of the bearing. This significant risk underscores the importance of proper lubrication practices in engine maintenance to prevent galling in such high-friction components. Other components like crankshaft bearings, piston rings, and connecting rods are designed with different operating principles, often incorporating mechanisms like oil films to separate surfaces, which helps reduce the likelihood of galling. While wear can occur in any of these parts under extreme conditions, the mechanics of the ball bearing assembly make it the most likely candidate to experience galling due to the sliding contact and stress involved.