Lubrication structure for four-stroke engine

A lubrication structure for a four-stroke engine configured to lubricate driving parts by supplying oil stored in an oil tank provided separately from a crank chamber, using pressure fluctuation in the crank chamber, the lubrication structure comprising:

• a first circulating route configured to supply the oil from the oil tank to the crank chamber and return oil mist generated in the crank chamber to the oil tank;
• a second circulating route configured to supply the oil mist from the oil tank to a valve operating mechanism and return to the oil tank;
• a discharge passageway configured to discharge blowby gas contained during circulation of the oil from the second circulating route to a combustion chamber;
• and
• a partition wall configured to separate between the crank chamber and the oil tank, wherein:
• a central part of the partition wall is located vertically above a surface of the oil stored in the oil tank even if an engine body is tilted;
• and
• an opening A1 of the second circulating route is formed in the central part, the oil mist being supplied from the opening A1.