Abstract: To provide a sealing structure for a cylinder and a cylinder head, which is significantly effective for a reciprocating type internal combustion engine in which a cylinder and a cylinder head are detachably connected with each other through a gasket. An end portion, on the side being in contact with the cylinder head, of the cylinder bore of the cylinder sleeve in the cylinder block has a notched conical surface as a notched inclined surface whose inside diameter gradually enlarges from the inner peripheral-surface of the cylinder bore toward the contact end surface with the cylinder head. An outer peripheral portion, on the cylinder side, of an endless ring-like gasket made of soft steel or stainless steel interposed between the cylinder block and the cylinder head has a taperingly conical surface as a taperingly inclined surface capable of being brought in close contact with the notched conical surface of the cylinder bore.

Abstract: A valve control device including a decompression cam. The decompression cam fits loosely on the camshaft adjacent to a valve motion cam. The decompression cam may be selectively moved and retained so as to extend beyond the valve motion cam to control the associated cam follower during the compression stroke. An eccentric weight is associated with the decompression cam so as to draw it from an extension beyond the valve motion cam under normal operating conditions. When starting, a spring biases the decompression cam outwardly so as to interlock the cam with a projection associated with the camshaft. When the projection retains the decompression cam outwardly against the cam follower, an associated engine valve is partially open to reduce compression during the compression stroke. Further rotation releases the decompression cam from the projection and allows the centrifugal force operating on the eccentric weight to draw the decompression cam out of operation for normal running.

Abstract: A centrifugal clutch employing a clutch outer, a clutch inner and an arrangement of alternating clutch outer and clutch inner plates. The clutch is actuated by means of an annular piston residing within a cylinder which accumulates oil. Centrifugal forces are generated within the oil to create a pressure which forces the annular piston to compress the clutch plate arrangement. An outlet is provided controlled by a valve about the periphery of the cavity defined by the piston. A clutch actuation means controls the outlet valve to provide for disengagement of the clutch even under rapid rotation.

Abstract: A device for cooling both a belt casing of an engine and the engine itself, in which both the inside and the outside of the belt casing are cooled by exterior air which is sucked in by respective fans. The air which cools the outside of the belt casing also is used to cool the rest of the engine, and then exits the engine at a side opposite the side at which the air first was sucked in. As a result, air flow through the engine does not impede rotation of the fans and hence does not hamper the cooling process.

Abstract: Motorcycles of the type having front leg shields, step floors and rear mounted engines have water-cooled engines with radiators mounted at the front leg shield. Tubes connecting the radiator with the water-cooled engine extend below the step floor. In certain of the embodiments, a trunk is illustrated within which the filler cap and the radiator tank are positioned for easy access. The trunk may be mounted above and spaced from the front fender to define a passage for frontal air to be directed to the front mounted radiator.

Abstract: A motorcycle having a water-cooled engine. The cooling system includes a radiator located in a hollow front leg shield of the motorcycle. The radiator may be positioned on one side of the down tube while a radiator tank is located on the other. A damper mechanism is disclosed which allows selected flow of heated air from the radiator to be directed toward the rider for warmth. Alternately, heated air flows from the radiator downwardly from the hollow interior of the front leg shield.

Abstract: A swing type power unit for a two-wheeled motor vehicle including a four-cycle engine. The engine has an output shaft disposed in a transmission case adjacent to its front end. The case has its rear end portion provided with a rear wheel drive shaft, and has a wet type multi-stage power transmission mechanism disposed between the output shaft of the engine and the rear wheel drive shaft. The transmission case has front end pivotally secured to a vehicle body, and has the rear end to the body through a shock absorber. Oil lubrication for the engine and the power transmission mechanism is performed by oil accumulated in and at a bottom of said transmission case.

Abstract: A change speed transmission device using gears employs a shift drum mounted parallel to the driving and driven shafts. The shift drum is turned one-quarter revolution at a time to cause a shifting mechanism to produce a low speed drive, and an intermediate speed drive, and a high speed drive between the shafts, and then back to neutral. A pivoted pawl engages an abutment on the shaft drum to limit turning movement of the drum. An element frictionally engages a member fixed to rotate with the driven shaft and serves to bias the pawl to engage the abutment so that the shift drum is prevented from turning directly from a high speed shift position to a low speed shift position.

Abstract: A power transmission device of a motorcycle comprising a main transmission case formed integrally with an engine crank case and accommodating a main transmission, and a sub-transmission case provided at the rear side of the main mission case. The sub-transmission case accommodates a sub-transmission which is drivingly connected to the main transmission and also to a rear wheel of the motorcycle through a transmission mechanism. The transmission mechanism and the sub transmission are disposed at opposite sides of the rear wheel. The sub-transmission case is composed of a case body and a cover for covering an opening of the case body. The opening is formed at a lateral side of the gears of the sub-transmission so that the gears are accessible and replaceable by removing the cover from the opening.

Abstract: A power transmission apparatus of the type having a crankshaft of an internal combustion engine and an intermediate driving shaft to be driven by the crankshaft. Input and output shafts of a gear transmission to be driven by the driving shaft are so provided in an outer surrounding machine casing as to be arranged in parallel rows to one another. The four shafts are positioned, at their axial lines, in a common plane, and the machine casing is so constructed as to be divisible at that plane into upper and lower half portions.