Harmful vapors which may be formed within the engine are removed from the crankcase, gear train, and valve
compartment by a continuous pressurized ventilating system.
A slight pressure is maintained in the engine crankcase by the seepage of a small amount of air from the airbox
past the piston rings. This air sweeps up through the engine and is drawn off through a crankcase breather.
In-line engines are equipped with a breather assembly attached to the valve rocker cover (Fig. 1) or a breather
assembly mounted on the flywheel housing (Fig. 2).
It is recommended that the breather tube be inspected and cleaned, if necessary, to eliminate the possibility
Figure 1. Typical Crankcase Breather Mounting
Figure 2. Crankcase Breather Mounting and Details (In-Line Engine)