Abstract: In a valve train of an internal combustion engine, an input sprocket mounting portion is provided on one end of an exhaust camshaft, and a valve operating cam portion is formed on the other end of the camshaft. A decompression shaft of a decompression device is inserted in a decompression shaft hole, which is formed from the input sprocket mounting portion toward the valve operating cam portion. The decompression shaft hole is formed at a position offset from an axis of the camshaft. A camshaft inner oil passage is formed in the camshaft to extend from one end toward the other end of the camshaft in parallel arrangement to the decompression shaft hole to supply lubricant from the bearing journal portion to the bearing journal portion. The above arrangement makes it possible to supply a sufficient amount of lubricant oil to slide portions of the valve train of a saddle riding vehicle.

Abstract: A cam chain tensioner device of an internal combustion engine includes a cam chain tensioner, and a tensioner lifter pressing the cam chain tensioner to a cam chain. The tensioner lifter is mounted on an inclined upper surface of the cylinder head. The cylinder head has therein a valve train oil supply passage supplying oil from an oil pump to the valve train camshafts, and a tensioner lifter oil supply passage supplying oil to the tensioner lifter. The valve gear oil supply passage has a branching portion where the tensioner lifter oil supply passage branches. The branching portion is at a position higher than the tensioner lifter, and communicates with the tensioner lifter disposed at a position lower than the branching portion. It is thus possible to prevent fluttering of the cam chain and to reduce noise generated by the cam chain at the time of restart of the engine after it is stopped.

Abstract: In a saddle-ride type vehicle in which a cylinder head of a single-cylinder engine main unit has a front wall and a rear wall, an exhaust system being connected to the front wall and an intake system being connected to the rear wall, a joining surface of the cylinder head to a head cover is formed on a plane crossing a cylinder axis, the plane being inclined downward toward a front. Rotation axes of camshafts are arranged on the plane. An axis of a valve stem of a throttle valve is arranged on the plane. A curve cover curved so as to cover driven sprockets fixed to the camshafts is formed on one side in a vehicle width direction of the head cover. A drum housing box housing a throttle drum fixed to one end of the valve stem is arranged close to the curve cover.

Abstract: In a DOHC-type internal combustion engine in which a pair of intake valves and a pair of exhaust valves are disposed around a plug hole, and two pairs of rocker arms are respectively interposed between intake-side and exhaust-side camshafts and the intake valves and the exhaust valves, first and second support portions of one pair of the rocker arms are disposed between the intake valves and the exhaust valves in a direction orthogonal to axes of the intake-side and exhaust-side camshafts and around the plug hole, and the third and fourth support portions of an other pair of the rocker arms are disposed outside a region between the intake valves and the exhaust valves in the direction orthogonal to the axes of the intake-side and exhaust-side camshafts.

Abstract: A cam chain tensioner device of an internal combustion engine includes a cam chain tensioner, and a tensioner lifter pressing the cam chain tensioner to a cam chain. The tensioner lifter is mounted on an inclined upper surface of the cylinder head. The cylinder head has therein a valve train oil supply passage supplying oil from an oil pump to the valve train camshafts, and a tensioner lifter oil supply passage supplying oil to the tensioner lifter. The valve gear oil supply passage has a branching portion where the tensioner lifter oil supply passage branches. The branching portion is at a position higher than the tensioner lifter, and communicates with the tensioner lifter disposed at a position lower than the branching portion. It is thus possible to prevent fluttering of the cam chain and to reduce noise generated by the cam chain at the time of restart of the engine after it is stopped.

Abstract: In a valve train of an internal combustion engine, an input sprocket mounting portion is provided on one end of an exhaust camshaft, and a valve operating cam portion is formed on the other end of the camshaft. A decompression shaft of a decompression device is inserted in a decompression shaft hole, which is formed from the input sprocket mounting portion toward the valve operating cam portion. The decompression shaft hole is formed at a position offset from an axis of the camshaft. A camshaft inner oil passage is formed in the camshaft to extend from one end toward the other end of the camshaft in parallel arrangement to the decompression shaft hole to supply lubricant from the bearing journal portion to the bearing journal portion. The above arrangement makes it possible to supply a sufficient amount of lubricant oil to slide portions of the valve train of a saddle riding vehicle.

Abstract: In a DOHC-type internal combustion engine in which a pair of intake valves and a pair of exhaust valves are disposed around a plug hole, and two pairs of rocker arms are respectively interposed between intake-side and exhaust-side camshafts and the intake valves and the exhaust valves, first and second support portions of one pair of the rocker arms are disposed between the intake valves and the exhaust valves in a direction orthogonal to axes of the intake-side and exhaust-side camshafts and around the plug hole, and the third and fourth support portions of an other pair of the rocker arms are disposed outside a region between the intake valves and the exhaust valves in the direction orthogonal to the axes of the intake-side and exhaust-side camshafts.

Abstract: In a saddle-ride type vehicle in which a cylinder head of a single-cylinder engine main unit has a front wall and a rear wall, an exhaust system being connected to the front wall and an intake system being connected to the rear wall, a joining surface of the cylinder head to a head cover is formed on a plane crossing a cylinder axis, the plane being inclined downward toward a front. Rotation axes of camshafts are arranged on the plane. An axis of a valve stem of a throttle valve is arranged on the plane. A curve cover curved so as to cover driven sprockets fixed to the camshafts is formed on one side in a vehicle width direction of the head cover. A drum housing box housing a throttle drum fixed to one end of the valve stem is arranged close to the curve cover.

Abstract: An internal combustion engine for a small planing boat for reducing the lateral width of an oil pan in conformity to the configuration of the bottom while securing the filtering surface area of an oil strainer. In addition, a vertical width of the oil pan is maintained to be small to thereby lower the total height of the internal combustion engine. In an internal combustion engine for a small planing boat, an oil pan is provided at the bottom portion of the internal combustion engine with an oil passage for communicating with an oil pump being formed inside the oil pan. A vertical wall of the oil passage is partially cut away to form communication openings each communicating between the inside and outside of the oil passage with the oil strainers being interposed in the communication openings substantially vertically to divide the oil passage into inside and outside.

Abstract: An internal combustion engine for a small planing boat for preventing supercooling of the internal combustion engine before warm-up while enabling efficient cooling of the internal combustion engine after warm-up. An internal combustion engine for a small planing boat includes a first cooling water path B through which cooling water introduced from a jet propulsion pump flows toward an internal combustion engine main body via an exhaust manifold. A second cooling water path C is provided through which cooling water introduced from the jet propulsion pump flows toward an exhaust pipe via an oil cooler. A bypass cooling water path D is provided for branching a part of cooling water in the second cooling water path C which flows out from the oil cooler, so as to merge into cooling water in the first cooling water path B which flows into the internal combustion engine main body.

Abstract: To provide an inner shim that is unlikely to fall off from a spring retainer even when an anomalous operation of a valve occurs. A spring retainer fixed to the upper end portion of a valve shaft has a shim-attachment hole. An inner shim is fitted into the shim-attachment hole. The bottom face of the inner shim is in contact with the upper end portion of the valve shaft, and the top face of the inner shim is positioned below the upper edge of the shim-attachment hole. A tappet is disposed above the spring retainer, and is allowed to move freely in the axial direction of the valve shaft. A shim-holding projection sticks out from the under face of the tappet, and extends downward. The projection enters, from above, the inside of the shim-attachment hole, and is in contact with the top face of the inner shim.

Abstract: An air intake structure for a small watercraft for ensuring the capacity of an inter-cooler and for connecting the inter-cooler to a supercharger by a simply shaped communicating portion. In an air intake structure for a small watercraft, an intake passage and an exhaust passage can be disposed on the left side and the right side, respectively, of a plurality of cylinders. A turbocharger is disposed rearwardly of the engine with the turbocharger is connected to an intake passage via an inter-cooler. In addition, the inter-cooler is disposed rearwardly of the engine, with the distribution passage being disposed forwardly of and on the left side of the inter-cooler so as to extend in the forward and rearward direction. The inter-cooler is connected to the rear end of the distribution passage with an intake pipe contiguous to cylinders being bent rearwardly along a side surface of the engine body.

Abstract: A lubricating apparatus for an internal combustion engine is provided in which an oil discharge passage, extending from the oil pump, is provided for straddling the oil pump case and the tank body. A direction of the extension of the oil discharge passage is changed in the tank body such that the oil discharge passage further extends in parallel with a junction plane between the oil pump case and the tank body. An opening for pressure reception by a relief valve is provided in the oil discharge passage portion extending in parallel with the junction plane. By attaching the oil pump case such that an outside end portion of the relief valve is held by a portion of the oil pump case, the relief valve is fixed between the tank body and the oil pump case.

Abstract: An improved snowmobile component layout structure includes an engine provided at front portion of the vehicle body, a cylinder head of the engine is inclined by an angle ? rearwards from a vertical axis, a steering shaft extends forwardly of the engine, and an air intake system, including an air cleaner, is provided at the rear side of the engine. In addition, a rider seat is provided on the rear side of the engine, and an elongated fuel tank is provided below the seat. The air cleaner has an improved disposition between the fuel tank and the engine. The inventive configuration narrows the spacing between an engine and a rider and concentrates mass to enhance turning performance.

Abstract: Providing a mounting structure for an internal combustion engine on a small planing boat on which an internal combustion engine for driving a jet propulsion pump is mounted, in a boat body between a hull and a deck, with a crankshaft thereof oriented in a front-rear direction of the boat body and on which a cylinder of the internal combustion engine is slantly disposed to one of left and right sides of the boat body, the mounting structure taking a weight balance of the internal combustion engine into account. A distance between an axis of the crankshaft and one mounting bracket arranged on a side where the cylinder of the internal combustion engine is slantly disposed, is longer than a distance between the axis of the crankshaft and the other mounting bracket arranged on the opposite side thereof.

Abstract: An internal combustion engine for a small planing boat for reducing the lateral width of an oil pan in conformity to the configuration of the bottom while securing the filtering surface area of an oil strainer. In addition, a vertical width of the oil pan is maintained to be small to thereby lower the total height of the internal combustion engine. In an internal combustion engine for a small planing boat, an oil pan is provided at the bottom portion of the internal combustion engine with an oil passage for communicating with an oil pump being formed inside the oil pan. A vertical wall of the oil passage is partially cut away to form communication openings each communicating between the inside and outside of the oil passage with the oil strainers being interposed in the communication openings substantially vertically to divide the oil passage into inside and outside.

Abstract: An internal combustion engine for a small planing boat for preventing supercooling of the internal combustion engine before warm-up while enabling efficient cooling of the internal combustion engine after warm-up. An internal combustion engine for a small planing boat includes a first cooling water path B through which cooling water introduced from a jet propulsion pump flows toward an internal combustion engine main body via an exhaust manifold. A second cooling water path C is provided through which cooling water introduced from the jet propulsion pump flows toward an exhaust pipe via an oil cooler. A bypass cooling water path D is provided for branching a part of cooling water in the second cooling water path C which flows out from the oil cooler, so as to merge into cooling water in the first cooling water path B which flows into the internal combustion engine main body.

Abstract: A lubricating apparatus for an internal combustion engine is provided in which an oil discharge passage, extending from the oil pump, is provided for straddling the oil pump case and the tank body. A direction of the extension of the oil discharge passage is changed in the tank body such that the oil discharge passage further extends in parallel with a junction plane between the oil pump case and the tank body. An opening for pressure reception by a relief valve is provided in the oil discharge passage portion extending in parallel with the junction plane. By attaching the oil pump case such that an outside end portion of the relief valve is held by a portion of the oil pump case, the relief valve is fixed between the tank body and the oil pump case.

Abstract: To prevent a drop in a lubricating oil supply pressure in a valve train from occurring by disposing a lubricating oil supply path for the exclusive use of the valve train without allowing the lubricating oil to flow through an oil gallery, thereby securing a sufficient amount of supply of the lubricating oil in the valve train to enhance lubrication efficiency. A feed pump rotating with a crankshaft is disposed at a leftward end of the crankshaft. Lubricating oil supplied from the feed pump flows through an oil cooler and an oil filter. Part of the lubricating oil is supplied through a lubricating oil supply path to an oil gallery and to journals, crankpins, and the like of the crankshaft. The other part of the lubricating oil is supplied through lubricating oil supply paths for the exclusive use of the valve train.

Abstract: To provide an inner shim that is unlikely to fall off from a spring retainer even when an anomalous operation of a valve occurs. A spring retainer fixed to the upper end portion of a valve shaft has a shim-attachment hole. An inner shim is fitted into the shim-attachment hole. The bottom face of the inner shim is in contact with the upper end portion of the valve shaft, and the top face of the inner shim is positioned below the upper edge of the shim-attachment hole. A tappet is disposed above the spring retainer, and is allowed to move freely in the axial direction of the valve shaft. A shim-holding projection sticks out from the under face of the tappet, and extends downward. The projection enters, from above, the inside of the shim-attachment hole, and is in contact with the top face of the inner shim.