Lubricating system for horizontal cylinder overhead valve engine

A lubricating system for an internal combustion engine having:

• a cylinder with a substantially horizontal axis and a valve at the head thereof;
• a crank chamber for accumulating lubricating oil;
• an air-oil separating chamber for accomodating a part of a mechanism for operating said valve;
• a breather passage connecting said crank chamber and said air-oil separating chamber for supplying oil mist to said valve operating mechanism;
• and
• a lubricating-oil returning passage which is disposed under said breather passage such as to connect said crank chamber and said air-oil separating chamber and through which said lubricating oil accumulated in said air-oil separating chamber flows toward said crank chamber,
• said system comprising means disposed in said breather passage in such a manner as to allow a fluid to flow solely toward said air-oil separating chamber and means disposed in said lubricating-oil returning passage in such a manner as to impart to the flow of said fluid toward said air-oil separating chamber a resistance higher than that of said fluid flow toward said air-oil separating chamber through said breather passage.