During a valve timing adjustment, what should be ensured about the marks on the gears?

During a valve timing adjustment, it is essential to ensure that the marks on the gears are aligned at top dead center. This alignment is crucial because top dead center (TDC) marks indicate the optimal position for the pistons in relation to the cylinder head. At TDC, the piston is at its highest point in the cylinder during the compression stroke, and the camshaft timing must be correctly aligned at this moment to ensure that valves open and close in sync with the piston movement.

Correct alignment at TDC is vital for the engine to run smoothly and efficiently. Any misalignment can lead to improper valve timing, which can cause performance issues such as misfires, loss of power, or even engine damage. Therefore, making sure that the timing marks are precisely aligned at TDC guarantees that the engine's valve timing is set correctly, allowing for optimal performance and longevity of the engine components.