4.5 Breather Operation

BREATHER OPERATION                                                                                                          4.5

GENERAL                                                           buildup of pressure caused by the downward force of the
                                                                  pistons.
As pistons push downward, displaced air in the crankcase is       From here, the intake system draws through the breather tube.
vented into the crank cavity. The blow-by gasses in the crank     This tube is installed into the lip seal on the centrifugal
cavity travel through the scavenge pump into the wet sump         separator engine breather assembly. From here the breather
cavity via the scavenge return passage. Blow-by gas then is       assembly spins with the cam for oil/air vapor separation to take
vented to the clutch cavity in the vent passage at the front of   place. Oil is then slung out of the centrifugal separator as it
the wet sump. The moving air absorbs a small amount of oil        spins, passing the oil separated vapor through the breather
vapor as it travels through the engine.                           bolt. It passes through the breather tube into the air box where
                                                                  it combines with the intake air stream and is burned during
From the clutch cavity, the blow-by gas flows up the chain
                                                                  normal combustion. Burning crankcase vapor eliminates the
tubes to the heads.
                                                                  pollutants normally discharged from the crankcase.
A centrifugal separator engine breather assembly is mounted
to the forward cylinder head intake camshaft to prevent a

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