Patent ID: 7980206

Claim:
A cooling water passage structure of a cylinder head in an internal combustion engine where cylinders are arranged in series in a longitudinal direction of the cylinder head and where exhaust ports of at least one pair of cylinders are merged with each other inside the cylinder head, wherein one end of the cylinder head in the longitudinal direction is provided with a cooling water inflow port leading to the inside of the cylinder head, another end of the cylinder head in the longitudinal direction is provided with an outflow port of main cooling water flow flowing through a center of the cylinder head and is provided with an outflow port of sub cooling water flows branched off from the main cooling water flow and flowing around the merged part of the exhaust ports located at a side part of the cylinder head, and an adapter communicated with the outflow port of the main cooling water flow and the outflow port of the sub cooling water flows and combining these outflow ports into a single cooling water outlet is fixed to an outer wall surface of the other end of the cylinder head.