The body of the Yiandi 645 series diesel engine is made of ordinary carbon steel plates welded together, except for the main bearing housing which is made of forged steel. Compared with the engine block of the 567 series diesel engine, the 645 series diesel engine has a larger air intake box, which can reduce the pulsation of intake and ensure uniform air supply to multiple cylinders. There is no water-cooled channel in the V-shaped Angle at the upper part of the machine body, which can reduce the thermal stress of the machine body and the deformation it causes. The crankshaft is forged from common carbon steel. The journal is quenched by induction heating. The diameter of the main journal is 190 millimeters and that of the connecting rod journal is 165 millimeters. The outer jacket of the piston is made of alloy cast iron material and adopts a freely rotating floating structure, which enables the piston to receive evenly distributed heat load and wear. The piston is cooled by the engine oil sprayed from the nozzle into the piston cooling chamber through oscillation. The service life of the piston can reach 25,000 hours. The cylinder liner with a water jacket is made of alloy cast iron. The 645 series diesel engines adopt a unitized fuel injector that integrates the high-pressure fuel pump and the fuel injector into one unit. Like the 567 series diesel engines, the 645 series adopts a combination of mechanical supercharging and exhaust gas turbocharging, ingeniously solving the supercharging problem of two-stroke diesel engines. When the diesel engine is under low load and the exhaust energy is very low, the crankshaft of the diesel engine drives the mechanical supercharger through gears. When the load of the diesel engine is high, the intake drives the turbine to rotate. This design can not only improve the acceleration and combustion quality of the diesel engine at low loads, but also give full play to the advantages of turbocharging at high loads.