Water-cooled four-cycle engine

In a water-cooled four-cycle engine, an engine core (2) including a cylinder block (3), a cylinder head (4) and a first crankcase half body (8a) is formed as a unitary part cast integrally; a water jacket (40) including a cylinder jacket (40a) surrounding a cylinder bore (3a) and a head jacket (40b) surrounding a combustion chamber (4a) is formed in the engine core (2); and a timing-belt chamber (13) being adjacent to the cylinder jacket (40a) is provided in a side portion of the engine core (2). A first opening portion (41) for forming a first semi-peripheral portion (40a1) of the cylinder jacket (40a) on a side opposite from the timing-belt chamber (13) by casting out is provided in a side surface of the cylinder block (3). A second opening portion (42) for forming a second semi-peripheral portion (40a2) of the cylinder jacket (40a) and the head jacket (40b) by casting out is provided in an upper surface of the cylinder head (4).