Engine valves are key components in the internal combustion engine's timing system in both gasoline and diesel engines. Their main function is to control the flow of the fuel-air mixture into the combustion chamber and to remove exhaust gases after the combustion process is completed. In four-stroke engines, which are most often found in vehicles, valves play an extremely important role in the engine's operating cycle.

Types of engine valves:

• Intake valves: They are responsible for supplying the fuel-air mixture (in petrol engines) or air (in diesel engines) to the combustion chamber. They are usually larger than exhaust valves to allow greater mixture flow into the combustion chamber.
• Exhaust valves: Allow exhaust gases to escape from the combustion chamber after the combustion process is completed. They are smaller than intake valves and made of a more heat-resistant material due to the high exhaust gas temperatures.

Construction of engine valves:

• Valve stem: The long, slender part that slides in the valve guide. It must be precisely made to ensure tightness and minimal friction.
• Valve head: The wider part that closes or opens a hole in the cylinder head. Contains a sealing surface that ensures tight closure of the valve.
• Valve disc: The part of the valve head that attaches to the valve seat in the cylinder head. It is responsible for sealing the combustion chamber during the engine operation cycle.