Valve stem seal and hermetic sealing structure

A hermetic sealing structure for hermetically sealing a space formed between a valve stem of a valve and a valve guide, the valve establishing and interrupting communication between a cylinder and a port, and the valve guide having one end facing a cam side and another end facing a cylinder side, the hermetic sealing structure comprising:

• a cylinder head;
• the valve guide arranged on the cylinder head;
• the valve stem inserted into the valve guide in a reciprocally movable manner;
• a valve spring mounted on the cylinder head, and biasing the valve stem in a direction where communication between the cylinder and the port is interrupted;
• and
• a valve stem seal provided on the valve guide on a side of the one end, wherein
• the valve stem seal includes:
• a reinforcing ring formed into an annular shape centered about an axis, and extending in a radial direction that is perpendicular to the axis;
• and an elastic body portion formed into an annular shape centered about the axis, directly attached to the reinforcing ring, and including a seal lip which abuts on the valve stem, and
• an entirety of the reinforcing ring is flat and a main surface of the reinforcing ring has one flat surface,
• the reinforcing ring is disposed between an inner wall of the cylinder head and the valve spring, and is fixed to the cylinder head by pressure from the valve spring.