AG Mechanics CDE Practice Exam

What is valve overlap?

1. Both valves are closed

2. Both valves are partially open

3. Both valves are open

4. Both valves are seated

The correct answer is: Both valves are closed

Valve overlap refers to the brief period in the engine's cycle where both the intake and exhaust valves are closed simultaneously. During this time, the piston is at the top of its stroke and both valves must be closed to create the necessary compression for the combustion process. This allows for better control over the air-fuel mixture and exhaust gases, optimizing engine performance. Options B, C, and D are incorrect because valve overlap does not involve both valves being partially open, both valves being fully open, or both valves being seated simultaneously. The correct answer is option A, where both valves are closed during valve overlap.