Why are inlet and exhaust valves fitted?

• A. To cover ports (or openings) in the cylinder heads.
• B. To regulate coolant temperature.
• C. To increase engine displacement.
• D. To lubricate the valve seats.

Answer: (A)

Valves are placed to regulate the flow of gases into and out of the combustion chamber. They precisely cover and seal the ports in the cylinder head, so when closed the chamber remains airtight and compression is maintained. The inlet valve opens at the right time to let the air-fuel mixture enter the cylinder, while the exhaust valve opens to allow the burnt gases to exit after combustion. Both valves return to the closed position and seal against their seats, aided by springs, to prevent leakage when not timed to open. If they didn’t cover the ports, there would be continuous leakage and lost engine efficiency. The other options aren’t the function of inlet and exhaust valves.