General; Crankcase Breathing System - Buell 2009 XB Series Service Manual

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CRANKCASE BREATHING SYSTEM

GENERAL

See Figure 3-102. Pressure created in the flywheel area on
piston downstroke is released through the reed valve into the
gearcase. From there a mixture of crankcase air and oil mist
is vented up the push rod covers to the upper rocker box.
See Figure 3-103. Air is allowed to escape the rocker boxes
by exiting the positive crankcase vent (PCV) valves (4) located
on top of the rocker boxes. From the PCV valves the air enters
the crankcase breather hoses (2, 3). The crankcase breather
hoses route through the air cleaner base plate (1) to the air
box where it is directed inside the air filter element and back
into the engine, mixed with combustion air.
The oil mist collects and eventually returns to the crankcase
through oil passageways in the cylinder head.
sm00209
Figure 3-102. Reed Valve Assembly in Gearcase
3-74 2009 XB Service: Engine
sm00216
1
4
5
6
1. Base plate, air box
2. Breather hose, rear
3. Breather hose, front
4. PCV Valves (2)
5. Grommet
6. Rocker cover (2)
Figure 3-103. Crankcase Breathing System
REED VALVE REPLACEMENT
NOTES
Whenever the gearcase cover is removed, inspect the
reed valve for cracks, chips and breakage.
See Figure 3-104. The reed valve (3) opens on the
downstroke to relieve crankcase pressure and closes on
the upstroke to prevent vapors returning to the crankcase.
The curved reed valve stop (2) limits the movement of the
reed valve.
1. Remove the fastener (1), the reed valve stop (2) and the
reed valve (3).
2. To replace the assembly, align the edges of the reed valve
(3) and the reed valve stop (2) to prevent premature failure
of the reed valve.
NOTE
It is not necessary to replace the reed block (4) along with the
reed valve. The block can only be replaced after separating
the crankcase halves.
3.15
3
2