FAA Powerplant Written Practice Test

What is created when grinding a valve to an interference fit?

1. A wide contact surface

2. A rough texture

3. A narrow contact surface

4. A smooth finish

The correct answer is: A narrow contact surface

When grinding a valve to achieve an interference fit, a narrow contact surface is established. This process involves precise machining where the valve and seat are shaped to create a tight fit between them. An interference fit is designed to ensure that when the valve is seated, there is minimal clearance between the two surfaces, which helps maximize sealing efficiency and reduce the possibility of leakage. The narrow contact surface results from careful grinding, allowing for a controlled amount of material removal to achieve the correct fit. This tight tolerance is essential in the application, as it ensures that the valve can withstand the pressures and temperatures present in the engine without compromising performance. The grinding process typically focuses on the edges or specific areas of the valve face, leading to this narrow contact area that enhances the sealing capabilities. In contrast, creating a wide contact surface would not support the purpose of developing an interference fit, as it would lead to excessive clearance and potential leakage. A rough texture would indicate poor machining quality, which could also adversely affect sealing performance, while a smooth finish, although desirable, isn't the primary focus in establishing an interference fit. The emphasis is on achieving a narrow, precise contact area to ensure effective sealing and engine efficiency.