Intake Valve
An engine valve that opens to allow the air-fuel mixture (in port-injected engines) or clean air (in direct-injected engines) to enter the cylinder.
The intake valve is a metal valve located in the cylinder head that acts as the entry gate for the air and fuel required for engine combustion. It is held closed by a heavy valve spring to seal the combustion chamber. When the camshaft rotates, its lobe pushes the valve open, allowing the engine to pull in fresh air and fuel during the intake stroke.
Intake valves are typically larger than exhaust valves to maximize the volume of air that can enter the cylinder, which directly influences engine horsepower and torque. Because they are continuously cooled by the incoming air and fuel mixture, intake valves operate at lower temperatures than exhaust valves. However, in modern direct-injection engines where fuel is sprayed directly into the cylinder rather than over the intake valve, the valves are prone to carbon buildup since they are no longer washed clean by fuel spray.
Problems with intake valves include carbon deposits on the valve stem and back face, bent valves (caused by timing belt failures), or burnt valves that fail to seal. Symptoms include engine misfires, rough idling, ticking noises, and loss of compression. Cleaning carbon buildup or replacing damaged valves requires removing the cylinder head and performing a valve job.