Valve Locks

Gases enter and exit the combustion chamber through ports, which are openings in the cylinder head. The valves regulate the flow of gases. One set of valves controls the intake, and the other set controls the exhaust. There are two sets of valves. When open, valves must restrict the passage of gases as little as possible; when closed, they must form a gas-tight seal.

The intake valve will be open throughout the intake stroke, allowing fuel and air to mix within. The exhaust valve will open on the exhaust stroke when the valve closes to let the compressed and burnt mixture to be driven out by the upward.