An internal combustion engine for an outboard motor for driving a vessel has an air guide system acting by way of a covering hood surrounding surfaces of the internal combustion engine and ancillary units. Covering hood inlet and outlet openings permit airflows to move in an interior space of the covering hood, and a fan driven by the internal combustion engine influences the airflows in the covering hood interior space. Airflows enter the interior space of the covering hood via an inlet opening and a first routing arrangement. Assisted by the fan, part of the airflows acts on the surfaces of the internal combustion engine and of the ancillary units. A second routing arrangement routs another portion of the airflows, as intake air, to an engine suction system. Airflows heated by engine and ancillary unit surfaces are conveyed by the fan and a third routing arrangement outside the covering hood.

A reciprocating internal combustion engine includes at least one piston, which is operatively connected by two connecting rods having two crankshafts rotating in opposite directions and running parallel to each other, which crankshafts are oriented in an upright manner to a horizontal water line of a boat, and an internal combustion engine housing of the internal combustion engine is composed of at least a cylinder crank housing and a cylinder head, having inlet and outlet valves, and is bounded by an upper end face and a bottom end face. To optimize the internal combustion engine, a joint ventilation system has an oil separating device provided with an oil pre-separator and a main oil separator, via which, when operating the internal combustion engine, a mixture of oil and leaking gas, resulting in a crankcase of the cylinder crank housing, reaches, by way of a discharge line extending adjacent to the upper end face, the oil pre-separator, from where the mixture of oil and leaking gas is led into the main oil separator and there is separated into the components of oil and leaking gas. The oil flows into an oil pan connecting at the bottom end face and the leaking gas near the upper end face flows into an intake system of the internal combustion engine.

An outboard motor includes an engine, a drive shaft, and a shift shaft disposed forward of the drive shaft. The shift shaft includes a first shift shaft that extends in an upward-downward direction, a second shift shaft disposed below the first shift shaft and spaced apart from and rearward of the first shift shaft, the second shift shaft extending in the upward-downward direction, and a shift force transmission to transmit, to the second shift shaft, a shift force applied to the first shift shaft.

An outboard motor includes an engine, a drive shaft, and a shift shaft disposed forward of the drive shaft. The shift shaft includes a first shift shaft that extends in an upward-downward direction, a second shift shaft disposed below the first shift shaft and spaced apart from and rearward of the first shift shaft, the second shift shaft extending in the upward-downward direction, and a shift force transmission to transmit, to the second shift shaft, a shift force applied to the first shift shaft.

An outboard motor includes a cylinder block, a cylinder head unit, a delivery pipe, a plurality of injectors, a fuel pump, and a fuel pipe. The cylinder block includes a plurality of cylinders. The cylinder head unit is connected to the cylinder block. The delivery pipe is attached to the cylinder head unit. The injectors are attached to the delivery pipe. The fuel pump is attached to the cylinder head unit. The fuel pipe is attached to the delivery pipe and the fuel pump. A first attachment direction of attaching the fuel pump to the cylinder head unit is parallel or substantially parallel to a second attachment direction of attaching the fuel pipe to the delivery pipe.

An outboard motor includes an exhaust passage that discharges exhaust gases generated in a V-type engine into water from an exhaust opening. The exhaust passage includes first and second branch passages connected to cylinders and disposed inside a V-shaped line, a first upstream collecting passage connected to each of the first branch passages, a second upstream collecting passage connected to each of the second branch passages, and a downstream collecting passage connected to the first and second upstream collecting passages. A portion from an upstream end of the downstream collecting passage to a downstream end of the downstream collecting passage is disposed outside cylinder heads of the V-type engine.

An outboard motor is provided with an upper separator disposed on the lower side of an oil case for storing a lubricating oil of an engine, and an extension case which is separably connected on the lower side of the upper separator. The upper separator has a central exhaust passage through which exhaust gas flows, and a cooling water flow part through which cooling water flows on the outside of the central exhaust passage, the central exhaust passage and the cooling water flow part forming an integrated structure. The exhaust gas and the cooling water are caused to mix in the extension case.

A marine propulsion device has an internal combustion engine; an intake manifold that delivers intake air from an upstream inlet to a downstream outlet for combustion in a plurality of piston-cylinders in the internal combustion engine; and a flame arrestor located in the intake manifold at the upstream inlet.

A marine propulsion system includes a marine propulsion device, a battery, and a controller. The marine propulsion device includes a propeller shaft, an engine, and an electric motor. The marine propulsion device transmits mechanical power from at least one of the engine and the electric motor to the propeller shaft. The battery supplies electric power to the electric motor. The controller controls the marine propulsion device such that the marine propulsion device is switchable among drive modes including a first drive mode and a second drive mode. In the first drive mode, mechanical power is transmitted from only the engine to the propeller shaft. In the second drive mode, mechanical power is transmitted from only the electric motor to the propeller shaft when the engine is in an idling state.

The invention provides an internal combustion engine comprising a piston mounted for reciprocating linear motion within a cylinder along a cylinder axis. The piston is coupled to an output shaft by a power transfer assembly arranged to convert linear motion of the piston to rotary motion of the output shaft. The piston has a first head moveable within a first chamber and a second head opposite the first head and moveable within a second chamber. The power transfer assembly has a lubrication system for lubricating moving components of the power transfer assembly. The lubrication system is sealed from the first chamber and the second chamber to prevent the passage of fluid from the lubrication system into the first chamber and the second chamber.