FAA Powerplant Written Practice Test

What is created as a result of grinding a valve to an interference fit?

1. A wide surface contact

2. A narrow surface contact

3. A rough texture

4. A polished edge

The correct answer is: A narrow surface contact

When a valve is ground to an interference fit, it results in a narrow surface contact. This is primarily because grinding involves removing material from the valve seat and the valve itself to create a smooth, precise fit that ensures effective sealing. An interference fit means that the two components are designed to fit together tightly, causing them to be pressed against each other with a limited contact area. A narrow surface contact is critical for achieving a reliable sealing surface, as it minimizes leakage and maximizes the effectiveness of the combustion process in an engine. Furthermore, this narrow contact area allows for higher pressure to be maintained within the cylinder, contributing to better engine performance. While surface texture and finish play roles in how the components interact, the goal of creating a narrow contact area ensures that the fit is both secure and efficient.