BREATHER CHAMBER OF INTERNAL COMBUSTION ENGINE

A breather chamber 7 of an internal combustion engine 4 includes looped cam chains 65L and 65R for transmitting power from a horizontally disposed crankshaft 31 to camshafts 61 L and 61 R provided in cylinder heads 43L and 43R, and includes cam chain chambers 63L and 63R disposed along side portions 46La and 46Ra of cylinder block portions 46L and 46R which intersect the direction of the crankshaft 31. The breather chamber 7 is located on a side of a plane P formed by a rotation locus L of the cam chain 65R in the direction of the crankshaft 31 in the cam chain chamber 63R. Thus, a breather chamber having a large size can be formed while an increase in the size of the internal combustion engine is suppressed.