An engine is provided with: a crank case that has a first crank shaft insertion hole and a second crank shaft insertion hole along the vertical direction; a crank shaft that is inserted into the first and second shaft insertion holes; and a cylinder unit that extends in the front-rear direction from the crank case. The cylinder unit is provided with a cylinder base that is positioned inside the crank case, and a cylinder block that is positioned outside the crank case. The cylinder unit is detachably attached to the crank case.

An engine (E) includes a crankcase body (19), a crankcase cover (20) covering a case opening portion (19b) of the crankcase body (19), a crankshaft (2), a cylinder base portion 21a located inside the crankcase body (19), a cylinder block (21b) located outside the crankcase body (19). The crankcase cover (20) is detachably attached to an upper portion of the crankcase body (19).

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.

A power unit includes: a crankcase which accommodates a crankshaft and a main shaft arranged in parallel to each other; a crank side cover which covers one end portion of the crankshaft from the outside in an axial direction of the crankshaft; a primary driven gear which is provided in the main shaft and meshes with a primary drive gear of the crankshaft; a clutch provided at one end portion of the main shaft; and a clutch cover which covers the clutch from the outside in an axial direction of the main shaft and is fastened and fixed to a packing surface provided on the crankcase to surround the clutch, wherein the primary driven gear and the packing surface overlap in a virtual straight line when viewed from the axial direction of the main shaft.

An internal combustion engine that can ensure an adequate cooling performance by using a small number of component parts, and can be minimized in size. The cooling device includes a boiling water cooling device including a water jacket, coolant piping, steam piping and a radiator, an air cooling fan connected to one end of a crankshaft projecting from an outer surface of the engine main body, and a cover member provided on the engine main body so as to cover the air cooling fan, and define a cooling air passage extending to a radiator core.

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).

Systems and methods for combustion engines with interchangeable components are described herein. An engine sub-assembly for a gasoline powered engine can include a crankcase having an opening extending at least through an upper surface thereof, the opening being configured to receive a crank arm therethrough, and a first mounting plate configured to be coupled with the crankcase. The first mounting plate can be selectively removable from the crankcase. The opening of the first mounting plate can generally align with the opening in the crankcase when the first mounting plate is coupled with the crankcase. The first mounting plate can be configured to receive a first cylinder block and to couple the first cylinder block to the crankcase. A second mounting plate can be configured to couple with a second cylinder block that is different than the first cylinder block and to couple the second cylinder block to the crankcase.

An engine is described having a crankcase, a liner and a head assembly. The crankcase is split along a plane defining a two part crankcase, where fluid passages are passing through only one of the crankcase portions, so as to not require crossing the split line. A connecting rod also includes a tapered end, and the piston has a complementary carrier receiving the connecting rod.

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.