The crankshaft is an important part of the engine. Its material is made of carbon structural steel or nodular cast iron. It has two important parts: the main journal, the connecting rod journal (and others). The main journal is installed on the cylinder block, the connecting rod neck is connected with the large head hole of the connecting rod, and the small connecting rod hole is connected with the cylinder piston, which is a typical crank slider mechanism.

The main bearing of the crankshaft is commonly called a large bearing. Like the connecting rod bearing, it is also a sliding bearing divided into two halves, namely the main bearing (upper and lower bearings). The upper bearing bush is installed in the main bearing seat hole of the body; the lower bearing is installed in the main bearing cover. The main bearing block and the main bearing cover of the body are connected together by the main bearing bolts. The material, structure, installation and positioning of the main bearing are basically the same as those of the connecting rod bearing. In order to convey oil to the connecting rod big head bearing, oil holes and oil grooves are usually opened on the main bearing pad, and the lower bearing of the main bearing is generally not open with oil holes and oil grooves due to the higher load. When installing the main bearing of the crankshaft, pay attention to the position and direction of the bearing.