Engine Oil System; Air Induction System; Carburetor And Priming System - Cessna 172 P Pilot Operating Handbook

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E N GI N E O I L S YS TE M
Oil for the engine lubrication is
supplied from a sump at the
bottom of the engine. The
capacity of the enfine sump is
seven quarts (one additional
quart is contained in the full flow
oil filter. Oil is drawn from the
sump through an oil suction
strainer screen into the engine-
driven oil pump. From the pump
oil is routed to a bypass valve. If
the oil is cold, the bypass valve
allows the oil to bypass the oil
cooler and go directly from the
pump to the full flow oil filter. If
I GN I TI O N -S TARTE R S YS TE M
Engine ignition is provided by
two engine-driven magnetos, and
two spark plugs in each cylinder.
The right magneto fires the lower
right and upper right spark-plugs.
Normal operation is conducted
with both magnetos due to the
more complete burning of the
fuel-air mixture with dual
ignition.
AI R I N DUCTI O N S YS TE M
The engine air induction system
receives ram air through an
intake in the lower front portion
of the engine cowling. The intake
is covered by an air-filter which
removes dust and other foreign
matter from the induction air.
Airflow passing through the filter
enters an airbox. After passing
through the airbox, induction air
CARBURE TO R AN D PRI M I N G S YS TE M
The engine is equipped with an
up-draft, float-type, jetcarburetor
mounted on the bottom of the
e n g i n e . T h e c a r b u r e t o r i s
equipped with an enclosed
accelerator pump, an idle cut-off
mechanism and a manual mixture
control. Fuel is delivered to the
carburetor by gravity flow from
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the oil is hot, the bypass valve
routes the oil out of the accessory
housing and into a flexible hose
leading to the oil cooler on the
right rear engine baffle. Pressure
oil from the cooler returns to the
accessory housing where it passes
through the full flow oil filter.
The filter oil then enters a
pressure relief valve which
regulates engine oil pressure by
allowing excessive oil to return
to the sump while the balance of
the oil is circulated to various
engine parts for lubrication.
Ignition and starter operation is
controlled by a rotary type switch
located on the left switch and
control panel. The switch is
labelled clockwise: OFF, R, L,
BOTH and START. The engine
should be operated on BOTH
m a g n e t o s e x c e p t
magnetochecks. The R and L
p o s i t i o n a r e f o r c h e c k i n g
enters the inlet in the carburetor
which is under the engine, and
is then ducted to the engine
cylinders through intake manifold
tubes. In the event carburetor ice
is encountered or the intake filter
becomes blocked, alternate
heated air can beobtained from
a shroud around an exhaust riser
through a duct to a valve in the
the fuel system. In the carburetor,
fuel is atomized, properly mixed
with intake air and delivered to
the cylinders through intake
manifold tubes. The proportion
of atomized fuel to air may be
controlled, within limits, by the
mixture control on the instrument
panel.
AIRPLANE & SYSTEMS DESCRIPTION
Residual oil is returned to sump
by gravity flow.
An oil filter cap/oil dipstick is
located at the right rear of the
engine. The filler cap/dipstick is
accesible through an access door
on the top right side of the engine
cownling. The engine should not
be operated on less that five
quarts of oil. For extended flight
fill to seven quarts (dipstick
indication only).
purposes and emergency use
only. When the switch is rotated
to the spring-loaded START-
position, the starter contactor is
energized and the starter will
crank the engine. When the
switch is released, it will
f o r automatically return to the BOTH-
position.
airbox operated by the carburetor
heat control on the instrument
panel. Heated air from the shroud
is obtained from an unfiltered
outside source. Use of full
carburetor heat at full throttle
w i l l r e s u l t i n
approximately 75 to 150 RPM.
For easy starting in cool weather,
the engine is equipped with a
manual primer. The primer is
actually a small pump which
draws fuel from the fuel strainer
when the plunger is pulled out,
and injects it into the cylinder
intake ports when the plunger is
pushed back in.
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