What is the position of the valves in a four-stroke cylinder engine during the compression stroke?

During the compression stroke of a four-stroke engine, both the intake and exhaust valves are closed. This is crucial because the compression stroke involves the piston moving upwards in the cylinder, compressing the air-fuel mixture (or just air in the case of a diesel engine) before the combustion event occurs. The closure of the valves ensures that the compression is efficient, allowing the engine to build up the necessary pressure and temperature in the cylinder for ignition.

If either valve were open during this stroke, it would lead to a loss of pressure and a failure to compress the mixture adequately, which would result in poor engine performance, misfires, or no ignition. Thus, having both valves closed is essential for proper engine operation during this phase of the four-stroke cycle.