Automotive Service Technician (310S) Engines Practice Exam

The section that makes direct contact with the valve seat is the valve face. When the valve closes, the valve face—the sealing surface at the edge of the valve head—contacts the valve seat machined into the cylinder head to form a gas-tight seal. The valve stem passes through the guide and does not seal, and the valve keeper is just the locking piece that holds the valve in place with the spring. The valve head is the overall end of the valve, but it’s the face that directly mates with the seat to stop gas flow.