FAA Powerplant Written Practice Test

What effect does excessive valve clearance have on valve opening duration?

1. Increases for both intake and exhaust valves.

2. Decreases for intake valves and increases for exhaust valves.

3. Decreases for both intake and exhaust valves.

4. No effect on valve opening duration.

The correct answer is: Decreases for both intake and exhaust valves.

Excessive valve clearance results in a decrease in valve opening duration for both the intake and exhaust valves. This phenomenon occurs because when the clearance is too large, the valve will close sooner after the camshaft has actuated it. As a result, the valve does not remain open as long as it should, leading to reduced effective opening durations. In engines, proper valve clearance is critical for ensuring that the valves open and close at the correct times as dictated by the camshaft profile. When the clearance is excessive, it can also negatively affect engine performance, as the engine may not receive the adequate amount of air and exhaust gases during the induction and exhaust strokes. Therefore, maintaining proper valve clearance is essential for optimal engine operation and efficiency. Understanding the relationship between valve clearance and opening duration is vital for diagnosing engine performance issues and ensuring that the engine runs smoothly and efficiently.