FAA Powerplant Written Practice Test

What is the role of burnishing crankshaft bearings during engine run-in?

1. To decrease engine temperatures

2. To ensure proper oil circulation

3. To create a smooth surface for better lubrication

4. To increase the friction coefficient

The correct answer is: To create a smooth surface for better lubrication

Burnishing crankshaft bearings during engine run-in plays a crucial role in creating a smooth surface for better lubrication. During the initial operation of an engine, particularly after assembly or overhaul, components such as crankshaft bearings experience a wearing-in process. This process is essential for achieving optimal contact between the bearing surfaces and the crankshaft, which allows for more effective lubrication. As the engine runs, the bearings undergo slight deformation and wear in a controlled manner, which helps to improve their surface finish. This enhanced smoothness reduces the potential for friction and wear, leading to more efficient operation and improved longevity of the engine components. Furthermore, smoother surfaces facilitate a more uniform film of oil to develop, which is vital for preventing metal-to-metal contact and ensuring that the bearings operate effectively under load. In contrast, options suggesting that the process is primarily about regulating engine temperatures or ensuring oil circulation do not address the primary objective of burnishing, which is to improve surface contact and lubrication. Similarly, increasing the friction coefficient is counterproductive to the aims of burnishing, which seeks to reduce friction levels for more efficient engine operation. Through this understanding, the process of burnishing emerges as a fundamental step in preparing crankshaft bearings for optimal performance in an engine.