PURPOSE: To prevent the leak of gas as well as attain the reduction of weight and simplification of assembling operations by a method in which the cylinder block and cylinder head of a Diesel engine are integrally molded of aluminium, and gas suction and exhaust ports are formed in the cylinder head.

CONSTITUTION: A cylinder block 10 and a cylinder head 11 are integrally molded of aluminium, and a cooling water chamber 12 is provided. A linear 31 forming the sliding face of a piston 6 is made of a cast iron and built in the block 10. An exhaust port 13, an air suction port 14, a cylindrical boss 20 to support the stems 17 and 18 of an exhaust valve 15 and an air suction valve 16, and a cylindrical boss 22 to form a fitting port for fuel injection nozzle 21 are formed in the head 11.