A camshaft includes, as a cam that opens and closes an exhaust valve and an intake valve, a ball cam whose protrusion amount changes according to rotation of the camshaft, wherein the camshaft has a double structure consisting of an inner shaft and an outer shaft provided in a manner that the inner shaft is helically displaced with respect to the outer shaft around an axis of the camshaft according to a rotation speed of the camshaft, and the ball cam is accommodated movably in a guide groove provided in the inner shaft and protrudes from the outer shaft, and a protrusion amount of the ball cam from the outer shaft changes when the ball cam moves in the guide groove due to the helical displacement of the inner shaft with respect to the outer shaft.

In an exemplary embodiment, an internal combustion engine, in which a valve is opened and closed when a piston reciprocates in a cylinder, has a configuration to perform repeatedly the following combined strokes: an intake stroke.fwdarw.a compression stroke.fwdarw.a combustion stroke.fwdarw.an exhaust stroke in a four-cycle internal combustion engine are combined with an intake and compression stroke.fwdarw.a combustion and exhaust stroke in a two-cycle internal combustion engine. The internal combustion engine can reduce pumping loss in a six-cycle internal combustion engine and increase the output.

A camshaft includes, as a cam that opens and closes an exhaust valve and an intake valve, a ball cam whose protrusion amount changes according to rotation of the camshaft, wherein the camshaft has a double structure consisting of an inner shaft and an outer shaft provided in a manner that the inner shaft is helically displaced with respect to the outer shaft around an axis of the camshaft according to a rotation speed of the camshaft, and the ball cam is accommodated movably in a guide groove provided in the inner shaft and protrudes from the outer shaft, and a protrusion amount of the ball cam from the outer shaft changes when the ball cam moves in the guide groove due to the helical displacement of the inner shaft with respect to the outer shaft.

In an exemplary embodiment, an internal combustion engine, in which a valve is opened and closed when a piston reciprocates in a cylinder, has a configuration to perform repeatedly the following combined strokes: an intake stroke.fwdarw.a compression stroke.fwdarw.a combustion stroke.fwdarw.an exhaust stroke in a four-cycle internal combustion engine are combined with an intake and compression stroke.fwdarw.a combustion and exhaust stroke in a two-cycle internal combustion engine. The internal combustion engine can reduce pumping loss in a six-cycle internal combustion engine and increase the output.

A decompression device is attached to an exhaust camshaft, and the exhaust camshaft is supported by a cylinder head. The decompression device includes a decompression camshaft formed with a decompression cam that can protrude and be immersed with respect to a base circle of an exhaust cam of the exhaust camshaft, a decompression arm that moves in an opening direction due to centrifugal force accompanying rotation of the exhaust camshaft to protrude the decompression cam, and a spring that moves the decompression arm in a closing direction by spring force resisting the centrifugal force to immerse the decompression cam. In the decompression device, the opening direction of the decompression arm can be changed in a same direction or in an opposite direction to a rotation direction of the exhaust camshaft for each cylinder.

An engine is disclosed of the V-configuration having an integrated engine and transmission. The engine has an engine ventilation system communicating between the crankcase and an upper end of the valve cover, whereby blow-by gases can be returned to the air intake system to recycle the unspent fuel. The engine also includes an easily accessible/removable cam, such that the camshaft may be removed without removing the rocker arms. The engine also includes a lubrication system for lubricating components of the engine and transmission.

An internal combustion engine for increasing the freedom of the layout of a rocker arm wherein the rocker arm is lighter. The internal combustion engine includes a camshaft having a first exhaust cam and a second exhaust cam, a first exhaust valve, and a second exhaust valve. The internal combustion engine further includes a first rocker arm for actuating the first exhaust valve to open and close, a second rocker arm for actuating the second exhaust valve to open and close, and a decompression mechanism for lifting the first rocker arm in a valve opening direction at the timing of a compression stroke initiated by the internal combustion engine. The first rocker arm and the second rocker arm are provided with an angular movement transmitter for transmitting a turning force produced by a decompression operator in the valve opening direction from the first rocker arm to the second rocker arm.

An internal combustion engine for increasing the freedom of the layout of a rocker arm wherein the rocker arm is lighter. The internal combustion engine includes a camshaft having a first exhaust cam and a second exhaust cam, a first exhaust valve, and a second exhaust valve. The internal combustion engine further includes a first rocker arm for actuating the first exhaust valve to open and close, a second rocker arm for actuating the second exhaust valve to open and close, and a decompression mechanism for lifting the first rocker arm in a valve opening direction at the timing of a compression stroke initiated by the internal combustion engine. The first rocker arm and the second rocker arm are provided with an angular movement transmitter for transmitting a turning force produced by a decompression operator in the valve opening direction from the first rocker arm to the second rocker arm.

A decompression device is attached to an exhaust camshaft, and the exhaust camshaft is supported by a cylinder head. The decompression device includes a decompression camshaft formed with a decompression cam that can protrude and be immersed with respect to a base circle of an exhaust cam of the exhaust camshaft, a decompression arm that moves in an opening direction due to centrifugal force accompanying rotation of the exhaust camshaft to protrude the decompression cam, and a spring that moves the decompression arm in a closing direction by spring force resisting the centrifugal force to immerse the decompression cam. In the decompression device, the opening direction of the decompression arm can be changed in a same direction or in an opposite direction to a rotation direction of the exhaust camshaft for each cylinder.