In an internal combustion engine for a saddle riding vehicle, in which a gear transmission and a shift drum of a shift change device is stored in a crankcase, the gear transmission having a plurality of transmission shafts parallel to a crankshaft extending in a vehicle width direction, a single pump shaft common to first and second oil pumps is rotatably supported by the crankcase. First oil pump rotors of the first oil pump are disposed at a mating face of a pair of left and right crankcase half bodies. A second oil pump rotor of the second oil pump is disposed between a pump gear and the first oil pump and at a side surface, on a side opposite to the mating face, of one crankcase half body out of the pair of left and right crankcase half bodies, the pump gear being arranged in the pump shaft.

An internal combustion engine includes a crankcase that defines a crank chamber, a crankshaft that has a crank housed in the crank chamber and is rotatably supported on the crankcase, a cylinder block that is joined to the crankcase and defines a plurality of cylinders in a horizontally-opposed arrangement, a to-be-detected body that rotates integrally with the crankshaft, and a detection sensor that extends through the crankcase from an upper face of the crankcase, is made to face a trajectory of the to-be-detected body, and generates a pulse signal in response to movement of the to-be-detected body. Thus, in a so-called horizontally-opposed internal combustion engine, a structure for disposing a detection sensor that can detect the angular velocity of a crankshaft with high precision is provided.

An internal combustion engine includes a crankcase that defines a crank chamber, a crankshaft that has a crank housed in the crank chamber and is rotatably supported on the crankcase, a cylinder block that is joined to the crankcase and defines a plurality of cylinders in a horizontally-opposed arrangement, a to-be-detected body that rotates integrally with the crankshaft, and a detection sensor that extends through the crankcase from an upper face of the crankcase, is made to face a trajectory of the to-be-detected body, and generates a pulse signal in response to movement of the to-be-detected body. Thus, in a so-called horizontally-opposed internal combustion engine, a structure for disposing a detection sensor that can detect the angular velocity of a crankshaft with high precision is provided.

An internal combustion engine (10) fitted with a carburetor (40) is provided with a fire-resistant cover member (62) having a front wall (65A) facing an air inlet port (44) of the carburetor, and a breather tube (60) having an inlet end (60A) connected to a crank chamber (28) of the internal combustion engine main body, and an outlet end (60B) supported by the cover member at a position located between the front wall and the carburetor.

An engine includes a crankcase in which a crank chamber that houses a crankshaft is formed, a cylinder block that is attached to the crankcase, and a cylinder that is formed with a sliding surface with respect to a piston. The crankcase includes a partition wall that forms the crank chamber. A lower end of the cylinder protrudes into the crank chamber from a lower end of the cylinder block, and a communicating hole that connects inside and outside of the cylinder is formed on a side surface of the cylinder as viewed in an axial direction of the crankshaft. The partition wall is formed with an opening that is communicated with the communicating hole.

An engine includes a crankcase in which a crank chamber that houses a crankshaft is formed, a cylinder block that is attached to the crankcase, and a cylinder that is formed with a sliding surface with respect to a piston. The crankcase includes a partition wall that forms the crank chamber. A lower end of the cylinder protrudes into the crank chamber from a lower end of the cylinder block, and a communicating hole that connects inside and outside of the cylinder is formed on a side surface of the cylinder as viewed in an axial direction of the crankshaft. The partition wall is formed with an opening that is communicated with the communicating hole.

An internal combustion engine includes: an engine body (10) having at least one cylinder; and an air-supply manifold (4) including an adjustment pipe (12). The length of the adjustment pipe is set so that a first pressure wave (14A) propagating from the air-supply manifold toward the adjustment pipe and a second pressure wave (14B) propagating from the adjustment pipe toward the air-supply manifold have opposite phases from each other at the cylinder.

An internal combustion engine includes: an engine body (10) having at least one cylinder; and an air-supply manifold (4) including an adjustment pipe (12). The length of the adjustment pipe is set so that a first pressure wave (14A) propagating from the air-supply manifold toward the adjustment pipe and a second pressure wave (14B) propagating from the adjustment pipe toward the air-supply manifold have opposite phases from each other at the cylinder.

An internal combustion engine assembly has a crankcase, a cylinder block connected to the crankcase, the cylinder block defining at least one cylinder, at least one piston disposed in the at least one cylinder, a crankshaft disposed at least in part in the crankcase and operatively connected to the at least one piston, and a flywheel operatively connected to and driven by the crankshaft. The crankshaft rotates in a first direction about a crankshaft axis. The flywheel rotates in a second direction opposite the first direction about the flywheel axis. A clutch selectively operatively connects the crankshaft to the flywheel. A marine outboard engine having the internal combustion engine assembly is also disclosed.

An internal combustion engine assembly has a crankcase, a cylinder block connected to the crankcase, the cylinder block defining at least one cylinder, at least one piston disposed in the at least one cylinder, a crankshaft disposed at least in part in the crankcase and operatively connected to the at least one piston, and a flywheel operatively connected to and driven by the crankshaft. The crankshaft rotates in a first direction about a crankshaft axis. The flywheel rotates in a second direction opposite the first direction about the flywheel axis. A clutch selectively operatively connects the crankshaft to the flywheel. A marine outboard engine having the internal combustion engine assembly is also disclosed.