FAA Powerplant Written Practice Test

What occurs when grinding a valve to create an interference fit?

1. The contact surface is widened

2. A narrow contact surface is created

3. A rough surface is achieved

4. Improper sealing is established

The correct answer is: A narrow contact surface is created

When grinding a valve to achieve an interference fit, a narrow contact surface is created. This process is intentional and essential for ensuring a tight seal between the valve and the seat during operation. An interference fit means that the dimensions of the valve stem are slightly larger than the valve seat, allowing for a precise and snug fit once the grinding is completed. Creating this narrow contact surface is critical because it promotes effective sealing, preventing leakage of gases or fluids during the operation of the engine. A properly ground valve will have a well-defined contact area that enhances the efficiency of the combustion process. The other potential outcomes mentioned do not align with the desired results of grinding valves. A widened contact surface would reduce sealing effectiveness, a rough surface could lead to increased wear and poor sealing, and improper sealing would be a consequence of inadequate fit rather than a goal of the grinding process. Thus, achieving a narrow contact surface is key to securing a proper interference fit in valve grinding.