COOLING STRUCTURE OF EXHAUST VALVE SEAT SECTION

PURPOSE:To select the temperature and the water flow of a valve seat at the optimum value for the cooling by providing an inlet port and an outlet port of the cooling water system different from a cylinder cooling system on the cooling water chamber formed inside the valve seat member. CONSTITUTION:An exhaust valve seat member 5 having an exhaust valve seat 5a and a cooling water chamber 5b is fitted into an engine cylinder cover 3, and an exhaust valve box 4 is fitted above it. A cooling water passage 2 is provided in the cylinder cover member, and the cooling water fed in through an inlet port 2a flows through the cooling water passages 2b, 2c in the valve box 4 then flows out through an outlet port 2d. On the other hand, the cooling water is fed into the valve seat cooling water chamber 5b through an inlet port 1 and the passage 1a in the valve box, and it flows out of an outlet port 1c through the passage in the valve box. The valve seat member cooling water passage is made independent of the cooling water system of the cylinder cover 2 and the valve box 4, thereby the temperature and the water flow of the valve seat can be set at the optimum value.