Main bearing for crank shaft of internal combustion machine

The invention provides a main bearing for the crank shaft of an internal combustion machine. The main bearing has an excellent performance on inhibiting air corrosion. The main bearing comprises a first semi-bearing and a second semi-bearing (41,42) formed in the axial direction groove (77) in the internal circumferential surface of the connection part. Each semi-bearing comprises a main cylinder part (71) the main cylinder part (71) comprises a circumferential center part and an extrusion releasing part (70), and the extrusion releasing part (70) extends in two directions; wherein the upward direction and the circumferential center part form an angle of 3 degrees, and the downward direction and the circumferential center part form an angle of 15 degrees. A plurality of extrusion releasing grooves (74,75) are formed in the circumferential direction in the form of connecting the axial direction grooves. An oil groove (41a) is formed on the first semi-bearing. The second semi-bearing comprises a moving zone (73), and the thickness of the moving zone (73) narrows down from the main cylinder part to the extrusion releasing part. The moving zone (73) comprises an internally protruded curve surface that protrudes towards to the radial direction from the axial direction.