The cylinder block is cast iron. The thickness of the walls of the cylinder block is reduced, and the rigidity of the cylinder block is increased by increasing its height. The cylinder block is sleeveless. To improve cooling and reduce oil consumption for waste, cruciform channels are made in the cylinder block through which coolant circulates, and oil channels are also made in the cylinder block for lubricating the crankshaft, connecting rods, pistons, oil supply to oil nozzles and to the cylinder head.