Abstract: A relief valve is interposed in an oil supply passage, and the relief valve internally includes a bottom passage for supplying oil from one oil supply passage to another oil supply passage. Since any branched oil passage for a relief valve is not required to be provided, it is possible to reduce the machining steps and machining cost. Further, since a space for disposing a branched oil passage is not required and the increase in space for disposing the relief valve can be reduced, the engine can be miniaturized.

Abstract: A lubrication system for an engine includes an oil discharge port in a lower section of a crankcase. A crankshaft, with a crank web attached thereto, rotates in a rotation direction within the crankcase. A first distance is formed between the crank web and a first inner surface of the crankcase, downstream of the oil discharge port. A second distance is formed between the crank web and a second inner surface of the crankcase, upstream of the oil discharge port. The first distance is less than the second distance. Also, the oil discharge port is defined in part by a back edge, which is wedge shaped and points in a direction opposite the rotation direction of the crankshaft. The back edge scoops oil from the crank web and into the oil discharge port.

Abstract: To provide a starter for an internal combustion engine which is capable of reducing a press-fit amount of a press-fit portion of a torque absorbing mechanism of a rotation transmitting means for transmitting the rotation of a kick shaft to a crank shaft, thereby enhancing the durability of the starter and making the starter compact. A kick-type starter for an internal combustion engine includes a rotation transmitting mechanism (a kick drive gear, a boss having a ratchet portion, a pinion gear, and an idler gear) for transmitting the rotation of a kick shaft to a crank shaft. The rotation transmitting mechanism is provided with a torque absorbing mechanism for absorbing an excessive torque due to an excessive input from the kick shaft. The torque absorbing mechanism is provided on the kick shaft, and includes a gear set composed of the boss having the ratchet and the pinion gear which are press-fitted to each other.

Abstract: A crankshaft rotation structure for a four cycle engine has a radial ball bearing fitted into a first main bearing section of a crankcase and a radial roller bearing fitted into a second main bearing section of the crankcase. The crankshaft is rotatably supported by the radial ball bearing and radial roller bearing. Furthermore, an oil jet nozzle for cooling a piston is provided in the second main bearing section. The diameter of the shafts for attachment of the bearings can be made the same, even if the outer diameter of the radial roller bearing is decreased compared to the outer diameter of the radial ball bearing. Accordingly, even if the oil jet nozzle is provided in the second main bearing section into which the radial roller bearing is fitted, the distance from the crankshaft center to the attachment position of the oil jet can be decreased and the engine itself can be reduced in size.

Abstract: An oil sump for lubricating oil is provided at a lower part of a crank chamber of a dry sump-type four-cycle engine. A reed valve is provided at an outlet of the oil sump which opens when pressure in the crank chamber is high. Furthermore, an oil passage slopes upwards from the outlet of the oil sump, with an outlet of the oil passage being provided above an oil surface level of oil accumulated within the engine. Oil from the outlet of the oil passage is smoothly discharged from the outlet of the oil passage without being discharged into the collected oil. Furthermore, oil mixed with air within the crank chamber is not directly mixed into the collected oil and oil oxidation is therefore prevented. Since there is no direct contact with high-temperature blow-by gas, etc., oil deterioration is suppressed.