at the downwind side of the cooling air with the push rod guide 10 g 3 communicating with the valve train area 10 g and therefore the valve train components not shown is mounted on the crankshaft 5 at the downwind side this means that the engine can be connected to the machine body including the crankshaft 5 and the fan 6 on the opposite side from the push rod guide 10 g 3 as with this embodiment with a shorter connection shaft length a shorter length of connection shaft between the crankshaft 5 and the fan 6 means less shaft wobbling and less vibration of the machine 1 in the case of the back pack blower 1 shown in fig8 in particular the load on the operator 39 s hip is reduced as the machine 1 can be mounted close to the back pack frame 21 that is the center of gravity of the machine 1 is closer to the hip of the operator the intake port 10 e the exhaust port 10 f and some of the vertical fins 10 d 1 etc are located around the bolt head shoulders 10 c where the joint condition between the cylinder 8 and the cylinder head 10 is ideal with this configuration the cylinder head 10 has high rigidity around the bolt head shoulders 10 c making it less likely that deformation occurs at the joint interface that is the cylinder 8 and the cylinder head 10 of this portable 4 cycle engine 2 have high surface.