Breather chamber structure for internal combustion engine

A breather chamber structure for an internal combustion engine, comprising:

• a crankcase;
• a cylinder body operatively mounted on an upper portion of the crankcase;
• a breather chamber configured to separate oil from oil mist in the crankcase, said breather chamber comprising:
• a crankcase side breather chamber formed in the crankcase and having an opening to a joining plane between the crankcase and the cylinder body, and
• a cylinder side breather chamber formed in the cylinder body and having an opening to the joining plane;
• said breather chamber spans the crankcase and the cylinder body for compactly forming the breather chamber on an upper face side of the crankcase;
• a transmission chamber configured to accommodate a transmission therein, said transmission being positioned in the crankcase and includes a main shaft having a plurality of gears connected thereto, said main shaft being operatively connected to a crankshaft positioned in the crankcase;
• wherein a breather chamber bottom wall partitions the transmission chamber and the crankcase side breather chamber from each other with a lowest portion of an exit opening of an oil return path being positioned lower than the breather chamber bottom wall, wherein oil is separated from oil mist and flows along the breather chamber bottom wall to the oil return path;
• a breather entrance opening, which communicates with the inside of the crankcase, is provided in the breather chamber bottom wall of the crankcase side breather chamber;
• and
• a gasket for partitioning the crankcase side breather chamber and the cylinder side breather chamber from each other is disposed between a top surface of the crankcase and a bottom surface of the cylinder body while a gasket communicating port for communicating the crankcase side breather chamber and the cylinder side breather chamber with each other is formed in the gasket.