The cylinder block should have sufficient strength and rigidity. According to the different positions of the installation plane of the cylinder block and the oil pan, the cylinder block is usually divided into the following three forms.

(1) The general cylinder block is characterized by the installation plane of the oil pan and the rotation center of the crankshaft at the same height. The advantages of this cylinder block are small height, light weight, compact structure, easy processing, and convenient disassembly and assembly of the crankshaft; but its disadvantage is poor rigidity and strength.

(2) The gantry cylinder block is characterized in that the installation plane of the oil pan is lower than the rotation center of the crankshaft. It has the advantages of good strength and rigidity, and can withstand larger mechanical loads; but its disadvantages are poor manufacturability, heavy structure, and difficult processing.

(3) Tunnel-type cylinder block The main bearing hole of the crankshaft of this type of cylinder block is an integral type, using rolling bearings, the main bearing hole is larger, and the crankshaft is installed from the rear of the cylinder block. Its advantages are compact structure, good rigidity and strength, but its disadvantages are high machining accuracy requirements, poor manufacturability, and inconvenient disassembly and assembly of the crankshaft.