PURPOSE: To enhance the durability by installing a water jacket, composed of an external angular cylindrical part made of pressed steel plate and an internal steel cylindrical part to be fixed to the abovementioned cylindrical part, between the cylinder head and crank case by pinching with a tension bar.

CONSTITUTION: Between the cylinder head 10 and crank case cast from an aluminum alloy, 1, an external angular cylindrical part, in which an upper- bottomed cylindrical part 2 made of pressed steel plate is butted watertightly with a lower-bottomed cylindrical part 3 made of pressed steel plate at the butt part 7, and an internal cylindrical part 4 to be fixed to the abovementioned cylindrical part constitute a water jacket 13, which is pinched by a tension bar 9. In the inner face 8 of said internal cylindrical part 4 is fitted a cylinder liner 5 by pressure or hot pressing. Thereby a cylinder block light in weight having good durability can be obtained.