AG Mechanics CDE Practice Exam 2025 - Free AG Mechanics Practice Questions and Study Guide

The correct answer is timing marks. The camshaft gear and crankshaft gear in an engine have specific timing marks that must be aligned properly. These timing marks ensure that the valves open and close at the precise moment, coordinating the engine's combustion process. Failure to align these timing marks correctly can result in the engine not running smoothly or potentially causing damage. Therefore, it is crucial to pay attention to these timing marks when working on an engine to ensure proper valve timing.

The other options, such as alignment marks, reference marks, and calibration marks, do not specifically refer to the timing relationship between the camshaft and crankshaft gears, making them incorrect choices for this question.