AG Mechanics CDE Practice Exam 2025 – The Comprehensive All-in-One Guide for Success

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.