A forcedly air-cooled engine.

摘要

In a forcedly air-cooled engine (1) a local high temperature portion (16) is adapted to be cooled effectively so that thermal distortion and thermal breakage of a cylinder (24) and/or a cylinder head (3) caused by such a local high temperature can be avoided. As the means for preventing thermal distortion, there is provided a cylinder jacket (17) for cooling part of its cylinder (24), provided in a partition wall (16) between the cylinder and its push rod chamber (18). As the means for preventing thermal distortion of the cylinder head (3), there is provided a cooling air passage (37) in a cylinder head (3) and a head jacket (33) for oil cooling around a divided combustion chamber (28) so as to circulate oil through the head jacket (33). Local high temperature portions of the cylinder and/or the cylinder head can thereby be effectively cooled.