Chain Lubrication; Construction And Operation Of Oil Pump - Stihl 009 User Manual

STIHL 009, 010, 011
7.

CHAIN LUBRICATION

7.1 Construction and
Operation of Oil Pump
Top:
Intake stroke
Bottom:
Delivery stroke
The oil pump is located on the clutch
side of the crankcase. It supplies
lubricating oil to the guide bar and
chain while the engine is running.
The pump consists of the pump
housing, end cover, the diaphragm
with plunger, compression spring,
check valve and oil filter.
The oil pump is not driven mechani-
cally. It is operated by the alternating
pressure in the crankcase. The oil
Schematic of oil pump
1 = Filter
2 = Feed bore
3 = Plunger with diaphragm
4 = Pulse chamber
5 = Compression spring
pump's pulse chamber is connected
to the crank chamber by a bore.
The upward stroke of the piston crea-
tes a depression in the crankcase
which is transferred via the housing
bore to the pulse chamber. This
causes the diaphragm to move back.
The plunger is attached to the dia-
phragm and opens the oil feed bore.
The ball check valve closes the oil
delivery bore at the same time and
the space between the check valve
and plunger fills with chain oil. The oil
must pass through a filter before it
enters the pressure chamber.
The pressure in the pulse chamber is
changed by the downward stroke of
the piston. This causes the
diaphragm to be moved in the
opposite direction and the plunger
forces the chain oil out of the
pressure chamber into a rubber hose
and from there to the cutting
attachment. A compression spring
between the diaphragm and the
pump cover assists the action of the
pressure against the diaphragm.
The oil delivery rate rises in an
almost linear ratio to engine speed
and, therefore, the chain speed. This
means there is always a sufficient
supply of lubricating oil to match
chain speed.
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