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.

The efficiency of charging air to a scavenging channel is enhanced by generating a gas flow in a piston groove simultaneously with the piston groove coming into communication with an air port. A piston groove 8 formed in a peripheral surface of a piston includes a pressure transmission through hole 10, and the pressure transmission through hole 10 consistently communicates with a crankcase. In the course of the piston moving up, upon a pressure in the crankcase becoming negative, the negative pressure in the crankcase affects the piston groove 8 through the pressure transmission through hole 10. Consequently, a pressure in the piston groove 8 is released to the crankcase through the pressure transmission through hole 10. Upon the piston moving up and the piston groove 8 being thereby brought into communication with the air port 4a, air enters the piston groove 8 through the air port 4a ((III) of FIG. 1).

The efficiency of charging air to a scavenging channel is enhanced by generating a gas flow in a piston groove simultaneously with the piston groove coming into communication with an air port. A piston groove 8 formed in a peripheral surface of a piston includes a pressure transmission through hole 10, and the pressure transmission through hole 10 consistently communicates with a crankcase. In the course of the piston moving up, upon a pressure in the crankcase becoming negative, the negative pressure in the crankcase affects the piston groove 8 through the pressure transmission through hole 10. Consequently, a pressure in the piston groove 8 is released to the crankcase through the pressure transmission through hole 10. Upon the piston moving up and the piston groove 8 being thereby brought into communication with the air port 4a, air enters the piston groove 8 through the air port 4a ((III) of FIG. 1).

An internal combustion engine has both a primary fuel system and a starting fuel intake assembly. The primary fuel system and the starting fuel intake assembly provide separate flow paths to a common chamber of the internal combustion engine. An external starting fuel source is fluidly connectable with the starting fuel intake assembly of the internal combustion engine, for instance when exposed to a low ambient temperature environment. The internal combustion engine is started while a starting fuel is flowing into a combustion chamber for the internal combustion engine. A primary fuel may also be flowing into the combustion chamber at this time. After the primary fuel is being consistently ignited in the combustion chamber, the flow of starting fuel to the combustion chamber may be terminated and the external starting fuel source may be fluidly disconnected from the starting fuel intake assembly of the internal combustion engine.

An internal combustion engine has both a primary fuel system and a starting fuel intake assembly. The primary fuel system and the starting fuel intake assembly provide separate flow paths to a common chamber of the internal combustion engine. An external starting fuel source is fluidly connectable with the starting fuel intake assembly of the internal combustion engine, for instance when exposed to a low ambient temperature environment. The internal combustion engine is started while a starting fuel is flowing into a combustion chamber for the internal combustion engine. A primary fuel may also be flowing into the combustion chamber at this time. After the primary fuel is being consistently ignited in the combustion chamber, the flow of starting fuel to the combustion chamber may be terminated and the external starting fuel source may be fluidly disconnected from the starting fuel intake assembly of the internal combustion engine.

In a single cylinder internal combustion engine in which a plug hole is provided striding between a cylinder head and a head cover, and an intake side camshaft and an exhaust side camshaft are disposed at positions sandwiching the plug hole therebetween, a long hole portion formed long in a direction orthogonal to axes of the camshafts is formed as a part of the plug hole. A part of a plurality of cam holder attaching bolts used for fastening the cam holder to the cylinder head are disposed within the long hole portion. A breather chamber disposed around the long hole portion is formed between the head cover and a breather plate attached thereto.

Disclosed is a method for controlling combustion in an internal combustion engine including, on the one hand, an air inlet pipe provided with an air flow regulator in the pipe and, on the other hand, a single cylinder associated with the regulator, and including the following steps: determining the engine speed and/or load; and when the speed is below a predetermined value and/or the engine load is below a predetermined value, the air flow regulator in the inlet pipe is operated in such a way that the air flow is temporarily reduced during the engine cycle compared with the position that the butterfly-type throttle valve occupies during the other strokes of the engine cycle, while an intake valve that lets air from the inlet pipe into the corresponding cylinder is open.

Disclosed is a method for controlling combustion in an internal combustion engine including, on the one hand, an air inlet pipe provided with an air flow regulator in the pipe and, on the other hand, a single cylinder associated with the regulator, and including the following steps: determining the engine speed and/or load; and when the speed is below a predetermined value and/or the engine load is below a predetermined value, the air flow regulator in the inlet pipe is operated in such a way that the air flow is temporarily reduced during the engine cycle compared with the position that the butterfly-type throttle valve occupies during the other strokes of the engine cycle, while an intake valve that lets air from the inlet pipe into the corresponding cylinder is open.

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.