True or False: Valves are held in the closed position by the valve guides.

Valves in an engine are typically held in the closed position by the force of the valve springs, not by the valve guides. The valve guides serve primarily to keep the valves aligned and to provide a channel for the valve stems to move up and down smoothly. The valve springs exert pressure on the valves, ensuring they remain closed when the engine is not activating them. This function is crucial for maintaining proper engine operation, as open valves during the wrong engine cycle would disrupt combustion and performance.

The options suggesting that the statement is true or conditionally true do not accurately reflect the primary role of valve guides. Valve guides do not possess the spring tension necessary to hold valves closed, which is an essential part of the engine's operation.