A linear reciprocating engine may include a cylinder having a first combustion chamber at one end and a second combustion chamber at an opposing end, first and second cylinder heads located at an end of the first and second combustion chambers, respectively, and a double-faced piston slidably mounted within the cylinder. The engine may further include a first piston rod portion extending from a first face of the double-faced piston through the first combustion chamber, and a second piston rod portion extending from a second face of the piston through the second combustion chamber. Passageways in the piston rod portions may be configured to communicate gases between the combustion chamber and a location outside the cylinder and configured to prevent gases from being exchanged between the cylinder and a location outside the cylinder via a path that crosses both face of the piston.

An internal combustion engine comprises an engine block defining a cylinder having a longitudinal axis A. A piston is arranged slidably within the cylinder and an impeller is arranged at one end of the cylinder. The impeller is rotatably mounted on a shaft, which extends out of the cylinder and which is driven in rotation by rotation of the impeller. The engine further comprises an anti-rotation formation to prevent the piston rotating about a longitudinal axis of the cylinder and a swirl-inducing vane arranged on the face of the piston which faces the end of the cylinder at which the impeller is arranged. Combustion gas generated by combustion of a fuel in the cylinder between the piston and the impeller is caused to swirl by reaction with the swirl-inducing vane and the swirling combustion gases, in turn, cause the impeller to rotate.

An exhaust device includes left and right exhaust pipes and mufflers connected to a downstream side of the left and right exhaust pipes. The pair of left and right exhaust pipes respectively includes a merging portion. A catalyst is provided to the merging portion respectively. The pair of left and right exhaust pipes respectively includes, on a downstream side of the catalyst, a branching portion that has one side thereof extending to the muffler and the other side thereof extending to a connecting pipe. An oxygen sensor is provided to one side on a downstream side of the pair of left and right branching portions.

An opposed piston engine includes an engine housing, at least one cylinder housing coupled to the engine housing, and at least one cylinder supported by the engine housing and by the cylinder housing along an exterior of the engine housing.

An opposed piston engine includes an engine housing, at least one cylinder housing coupled to the engine housing, and at least one cylinder supported by the engine housing and by the cylinder housing along an exterior of the engine housing.

A breather apparatus for an engine includes a breather chamber, one side portion and other side portion of the breather chamber, and a bottom face of the other side portion. The breather chamber is formed, along substantially half a circumference of a cylinder bore, in a cylinder block. The one side portion of the breather chamber is provided with a blow-by gas introduction hole leading blow-by gas in the crank chamber to the breather chamber and a one-way valve opening and closing the blow-by gas introduction hole. The other side portion of the breather chamber has a pipe connection hole connecting a breather pipe to the breather chamber and with a breather oil return passage. The bottom face of the other side portion projects into the crank chamber to a level lower than a bottom face of the one side portion.

An engine may include a cylinder having a first combustion chamber at one end thereof and a second combustion chamber at an opposing end thereof, first and second cylinder heads at an end of the first combustion chamber and the second combustion chamber, respectively, and a double-faced piston slidably mounted within the cylinder. The piston may be configured to move in a first stroke from the first end to the second end of the cylinder. The piston and the cylinder may be configured such that the first stroke includes an expansion stroke portion during which chemical energy from combustion in the first combustion chamber is converted into mechanical power of the piston, and a momentum stroke portion during which the piston continues to move to the second end of the cylinder and gases are exchanged between the first combustion chamber and a location outside the cylinder.

A small air-cooled internal combustion engine includes an aluminum engine block including a cylinder, a crankcase reservoir, and an outer surface, a piston positioned within the cylinder and configured to reciprocate within the cylinder, and a crankshaft coupled to the piston and configured to rotate about a crankshaft axis, wherein a portion of the crankshaft is located in the crankcase reservoir, where the outer surface of the engine block has an edge located a radial distance from the crankshaft axis and the radial distance is less than less than a standard minimum distance between the crankshaft axis and a horizontal mounting surface for a standard garden mounting flange for a horizontally-shafted engine.

Even in the case where a crankshaft extends in a substantially vertical direction, it is possible to reduce a situation that sprays of fuel injected from injectors may adhere to inner wall surfaces of intake passages, and it is possible to make the fuel supply to combustion chambers stable. Provided is a vertical engine including: a pair of intake passages (911a and 911b) which are arranged in an up and down direction with the interposition of a central axis of a cylinder (241) therebetween; a pair of intake valves (41L.sub.1 and 41L.sub.2) which open and close the pair of intake passages; and fuel injectors (70L.sub.1 and 70L.sub.2) which inject fuel to the pair of intake passages; wherein: the fuel injectors are arranged so that fuel injection directions by the fuel injectors can go not toward valve stems (411) of the intake valves provided in the upper and lower intake passages respectively but toward the backs of valve heads of the intake valves on a central axis (C1) side of the cylinder and the fuel injectors are disposed so that a central axis (FC2) of injection of the fuel injector into the lower intake passage can be closer to the central axis side of the cylinder than a central axis (CF1) of injection of the fuel injector into the upper intake passage.

An oil passage of an internal combustion engine including a crankcase, a cylinder block integrally connected to the crankcase, a piston operatively mounted within the cylinder block, a piston jet for providing oil to the piston within the cylinder block and a breather device integrally formed on the cylinder block wherein the breather device is in communication with the inside of the crankcase. An elevation of temperature of the oil which flows in an oil supply path is prevented thus allowing oil in the oil supply path to maintain a low temperature wherein the oil in the supply path is supplied to a piston jet formed on the internal combustion engine. An oil supply path through which oil is supplied to the piston jet is integrally formed on a wall body exposed to ambient air on a peripheral wall which forms the breather device.