What is the function of inlet and exhaust valves?

• A. To seal the crankcase from the atmosphere.
• B. To regulate oil flow to the piston.
• C. To admit fuel/air mixture and to provide an outlet for the spent combustion gases.
• D. To start the ignition sequence.

Answer: (C)

Inlet and exhaust valves control the engine’s breathing. Their job is to admit the air–fuel mixture into the cylinder and to provide an outlet for the spent combustion gases. The intake valve opens to let fresh charge in during the intake stroke, while the exhaust valve opens later to expel the combustion products after firing. Both valves must seal tightly to build compression and prevent leakage, and they are timed by the valve train so they open and close at the right moments in the cycle for efficient combustion. These valves aren’t responsible for sealing the crankcase, regulating oil flow, or starting the ignition; those functions belong to other systems.