intake valve allows the fuel-air mixture into the cylinder. The exhaust
valve lets the burnt gasses exit the cylinder. Springs and two stem
locks retain them in the head.
The valve itself has different areas: the valve head, valve face, and valve stem,
lock ring grooves, valve cap. When installed in the head valve guide, a seal is
placed on the stem between the head and the valve locking groves to prevent
excess oil from being pulled into the cylinder.