Breather arrangement for internal combustion engine

In a V-type internal combustion engine having cam shafts respectively provided in first spaces defined between cylinder heads and head covers of a pair of upwardly diverging cylinder banks, a breather arrangement comprising a pressure buffer chamber provided in a second space located between the cylinder banks of a cylinder block and including side walls constituted by cylinder block walls of said cylinder banks so as to be closed at an upper portion and communicated with an interior of a crankcase, and defining an approximately triangular cross-section, a communicating passage for communicating said pressure buffer chamber with an intake passage provided downstream of a throttle valve, the communicating passage provided with a pressure control valve for closing the communicating passage when an intake negative pressure is large and when the intake negative pressure is small, the communicating passage open at all other times of operation, a baffle plate provided in said pressure buffer chamber to confront an open end of said communicating passage and including a lid member for said baffle plate for separating oil from blow-by gas drawn from said crankcase and returning said oil to said breather chamber, said first spaces at least at one side of said banks in communication with the intake passage upstream of the throttle valve, a passage provided in the cylinder banks for providing communication between said first spaces and the crankcase, a main oil gallery extending through the cylinder block walls in an apex portion of said walls and, said cylinder block defining, at a side portion of said oil gallery, a plurality of communicating holes for communication with the crankcase.