Abstract: A compression ratio changing arrangement in an internal combustion engine. In order to change the compression ratio by utilizing, to the maximum, an eccentric amount between inner and outer peripheral surfaces of an eccentric ring interposed between a crank pin and a large end of a connecting rod in a compression ratio changing device, the eccentric ring is selectively connected to the crank pin or the large end of the connecting rod by a connecting pin with the thinnest portion or thickest portion of the connecting ring being turned toward the center of rotation of a crankshaft. The selective connection is performed when the piston is at botton dead center. When the eccentric ring has been connected to the crank pin, the stroke of the piston is increased or decreased by an amount corresponding to two times the eccentric amount of the eccentric ring without changing the position of the bottom dead center of the piston, as compared to the stroke with when the eccentric ring has been connected to the large end.

Abstract: A valve operating system in a multicylinder internal combustion engine, including an air pressure chamber biasing each engine valve in a closed direction thereof. The air pressure chambers are formed in a member positioned between the engine valves and the cam shaft and the member is formed with an air supply passage connected to the air pressure chambers for supplying air thereto and a relief passage connected to the air pressure chambers for releasing air therefrom. Air relief valves are provided in the member for individually releasing air from the air pressure chambers to the relief passage. A pressure control valve is connected to the relief passage for controlling pressure in the air pressure chambers for improving the accuracy of the operation of the relief valves and the control of the pressure in each the plurality of air pressure chambers.