Abstract: An internal combustion engine includes an engine body provided with a cylinder having openings for intake and exhaust, and valve bodies that open and close the openings, cam shafts provided with cam lobes that depress the valve bodies so as to open the openings, and bearing members that pivotally supports the cam shaft via lubricating oil. Each cam shaft includes cam journals pivotally supported by the bearing members, and a hollow bore extending in the axial direction of the cam shaft. When an area of the cam journal around the hollow bore is seen in a cross-sectional view perpendicular to the axial direction, a thickness on a projecting side of the cam lobe is X1, and a thickness on the opposite side to the cam lobe in the circumferential direction is X2, a relationship of X1>X2 is satisfied in at least a part of the cam journal.

Abstract: An internal combustion engine is provided, which includes an engine body provided with a cylinder having openings for intake and exhaust, and valve bodies that open and close the openings, cam shafts, each provided with a cam lobe that depress the corresponding valve body to open the openings, and bearing members pivotally supporting the cam shaft via lubricating oil. The cam shaft includes cam journals pivotally supported by the bearing members, and a recess formed at a position of the cam journal, opposing the cam lobe in the circumferential direction, and depressed radially inwardly of the cam journal, the recess being deeper in an axial end part of the cam journal than an axial center part.

Abstract: An internal combustion engine is provided, which includes an engine body provided with a cylinder and a piston reciprocatably accommodated in the cylinder, a crankshaft that converts reciprocating movement of the piston into rotational movement, and a bearing member pivotally supporting the crankshaft via lubricating oil. The crankshaft includes a crank journal pivotally supported by the bearing member, and a counterweight extending radially outward from an axial end part of the crank journal. The crank journal has a recess formed in a part thereof corresponding to the extended position of the counterweight, the recess being depressed radially inwardly. The recess is deeper at the axial end part of the crank journal than an axial center part.

Abstract: An internal combustion engine is provided, which includes an engine body provided with a cylinder and a piston reciprocatably accommodated in the cylinder, a crankshaft that converts reciprocating movement of the piston into rotational movement, and a bearing member pivotally supporting the crankshaft via lubricating oil. The crankshaft includes a crank journal pivotally supported by the bearing member, and a counterweight extending radially outward from an axial end part of the crank journal. The crank journal has a recess formed in a part thereof corresponding to the extended position of the counterweight, the recess being depressed radially inwardly. The recess is deeper at the axial end part of the crank journal than an axial center part.

Abstract: An internal combustion engine is provided, which includes an engine body provided with a cylinder having openings for intake and exhaust, and valve bodies that open and close the openings, cam shafts, each provided with a cam lobe that depress the corresponding valve body to open the openings, and bearing members pivotally supporting the cam shaft via lubricating oil. The cam shaft includes cam journals pivotally supported by the bearing members, and a recess formed at a position of the cam journal, opposing the cam lobe in the circumferential direction, and depressed radially inwardly of the cam journal, the recess being deeper in an axial end part of the cam journal than an axial center part.

Abstract: An internal combustion engine includes an engine body provided with a cylinder having openings for intake and exhaust, and valve bodies that open and close the openings, cam shafts provided with cam lobes that depress the valve bodies so as to open the openings, and bearing members that pivotally supports the cam shaft via lubricating oil. Each cam shaft includes cam journals pivotally supported by the bearing members, and a hollow bore extending in the axial direction of the cam shaft. When an area of the cam journal around the hollow bore is seen in a cross-sectional view perpendicular to the axial direction, a thickness on a projecting side of the cam lobe is X1, and a thickness on the opposite side to the cam lobe in the circumferential direction is X2, a relationship of X1>X2 is satisfied in at least a part of the cam journal.