A precision-machined poppet valve driven by the camshaft that controls the flow of the air or air-fuel mixture into the engine cylinder. It operates in extreme heat and must seal perfectly against its seat during the compression and combustion strokes. Carbon buildup on the back of this valve is a major issue in direct-injection engines, as no fuel washes over it to keep it clean.
We scoped the cylinders and found heavy carbon deposits on the back of every intake valve.
Related terms
Cylinder head
This cast metal component bolts to the top of the engine block to seal the combustion chambers.
Overhead valve
An engine design where the intake and exhaust valves sit in the cylinder head above the combustion chamber.
Variable valve timing
An engine technology that alters when intake and exhaust valves open and close.