Lubrication system for portable four-stroke engine

A lubrication system for a portable four-stroke engine configured to lubricate components in a valve-operating chamber and in a crank chamber with oil by supplying the oil by utilizing changes in pressure inside the crank chamber caused by reciprocating movement of a piston while circulating the oil, the valve-operating chamber accommodating intake and exhaust valve mechanisms therein, and configured to discharge blow-by gas in an oil circulation path from the valve-operating chamber to a combustion chamber through a breather passage connected to the valve-operating chamber, comprising:

• an opening end of the breather passage on a side of the valve-operating chamber that is disposed at substantially a center of the valve-operating chamber, wherein
• the valve-operating chamber is formed by attaching a valve-operating chamber cover, and
• the valve-operating chamber cover has a top plate portion and a side plate portion disposed along a circumferential edge of the top plate portion so as to be formed in a cap shape;
• an inner cover that is attached to an inner surface of the valve-operating chamber cover so as to be provided along and in contact with the inner surface of the valve-operating chamber cover;
• a suction passage that is formed as a gap between the circumferential edge of the top plate portion and the inner cover, the gap being formed by attaching the inner cover to the valve-operating chamber cover;
• three or more suction tubes that are in communication with the suction passage and provided in the inner cover, each of the suction tubes extending to the vicinity of an end surface of the valve-operating chamber which faces the top plate portion, each of the suction tubes having an opening end that is disposed in the vicinity of the end surface;
• and
• a direct passage by which the suction passage communicates with the crank chamber when a negative pressure is created in the crank chamber, wherein
• at least one of the opening ends of the three or more suction tubes is provided lower than the opening end of the breather passage in an aspect of use of the four-stroke engine
• the lubrication system is configured to generate oil mist inside the crank chamber and to deliver the oil mist to the valve-operating chamber;
• an oil reservoir, wherein at least a portion of the oil mist generated in the crank chamber is transferred to the oil reservoir and is directed into the oil reservoir by a communication passage having an opening that faces a surface of liquid oil in the oil reservoir, and
• a supply passage having a supply opening in the oil reservoir and connecting the oil reservoir to the valve-operating chamber, wherein the opening of the communication passage in the oil reservoir is disposed lower than the supply opening of the supply passage in the oil reservoir so as to protrude farther into the oil reservoir.