Types of Friction

Friction may be defined as the rubbing of one object or

another we.w
Surfaceagainst another. One surface sliding over OU fim between parts preventing metal-
surfacecauses sliding friction, as found in the use of plain to-metal contact, reducing friction
and
bearings. The surfaces are not completely flat or smooth
have microscopic defects that cause friction between the two

moving surfaces. [Figure 6-1] Rolling friction is created

when a roller or sphere rolls over another surface, such as
with ball or roller bearings, also referred to as antifriction

bearings. The amount of friction created by rolling friction is

less than that created by sliding friction and this bearing uses
an outer race and an inner race with balls, or steel spheres,
rolling between the moving parts or races. Another type of
friction is wiping friction, which occurs between gear teeth.
With this type of friction, pressure can vary widely and loads Flgure 6-2. Oilfilm acis as a cushon between two moving surfares

applied to the gears can be extreme, so the lubricant must be

ableto withstand the loads.

Oils clean theengine by reducing abrasive wearbypicking
up foreign particles and carrying them to a filter where thev
are removed. The dispersant, an additive, in the oil holds the
particles in suspension and allows the filter to trap them as the
oil passes through the filter. The oil also
Frction from metal-to-metal contact prevents corrosion
on theinterior ofthe engine by leaving a coating of oilon
parts when the engine is shut down. This is one of the reasons
why the engine should not be shut down for long periods of
time. The coating of oil preventing corrosion will not last on
theparts, allowing them to rust or corrode.

The engine's oilis thelife blood ofthe engine anditisvery

important for the engine to perform its function and to extend
the length between overhauls.

Figure 6-1. Two moving surfaces in direct contact create excessive

equirements and Characteristics of
Reciprocating Engine Lubricants
friction.
While there are several important properties that satisfactory
Functions of Engine Oil reciprocating engine oil must possess, its viscosity is m0st
In addition to reducing friction,
the oil film acts as a cushion important in engine_operation. The resistance of an oil
between metal parts. [Figure 6-2] This cushioning effect is to flow is known as its viscosity Oil that flows slowlyis
particularly important for such parts as reciprocating engine viscous or has a high viscosity; if it flows freely. it has a
crankshafts and connecting rods, which are subject to shock- lowviscosity. Unfortunately, the viscosity of oil is atfected
loading. As the piston is pushed down onthe powerstroke by temperature. It was not uncommon for earlier grades of
it applies loads between the connecting rod bearing and oil to become practically solid in cold weather, increasing
the crankshaft journal. Theload-bearingqualities of the oil drag and making circulation almost impossible. Other oils
must preventthe oilfilmfrom beingsqueezed ou,causing may become so thin at high temperatures that the oil filmis
ising
metal-to-metal contact in the bearing. Also, as oil circulates broken, causing a low load carrying ability, resulting in rapia
through the engine, it absorbs heat from the
pistons and
wear of the moving parts.
cylinder walls. In reciprocating engines, these components
are especially dependent on the oil for The oil selected for aircraft
cooling. engine lubricationmustbelight
enough to circulate freely at cold temperatures,yetheaY X
Oil cooling can account for up to S0 percent of the
total enough to provide the proper oil film at engine operatiug
engine cooling and is an excellent medium to transfer the temperatures. Since lubricants vary in properties andsin
heat from the engine to the oil cooler. The oil also aids in no one oil is satisfactory for all engines and all operaun
forming a seal between the piston and the cylinder wall to conditions,itisextremelyimportantthatonlytheappro X
prevent leakage of the gases from the combustion chamber. gradeor Society of Automotive Engineers (SAE) r
be used.
6-2
 The SAE letters oil container are not an endorsement
factors must be considered in determining the proper on an
each
or recommendation of the oil by the SAE. Although
eri
de ofoil to use in a particular engine, the most important of on its
ich are the operatung load, rotational speeds, and operating grade of oil is rated by an SAE number, depending
eratures. The grade of the lubricating oilto be used specific use, it may be rated with a commercial aviaton
mincd by the operating conditions to be met in the grade number or an Army and Navy specification number.
s ypes of engines. The oilusedinaircraftreciprocating The correlation between these grade numbering systems s
various
engines arelatively high viscosityrequired by: shown in Figure 6-3.

Large engine operating clearancesduetotherelatively

large size of themoving parts, the different materials
Commerclal Commerclal Army end Navy
sed, and the different rates of expansion of the various Avlatlon No SAE No. Specification No.
materials; 65 30 1065

30 40 1080
High operating temperatures; and
100 50 1100
High bearing pressures.
120 60 1120
140 70
Viscosty
Cenerally, commercial aviation oils are classitied by a Figure 6-3. Grade designations for aviation oils.
nuamber, (suchas80,100.140,etc.) that is an approximation
the viscosity as measured by atestung instrumept called Viscosity Index
Saybolt Universal ViscoSimeter. In this instrument, a The viscosity index is a number that indicates the eftect or
ubeholds a specific quantity of the oil to be tested. The oil is
brought to an exact temperature by a liquid bath surrounding perare CnangesS on the viscosity of the oil. When oil has
a
thetube.The time in seconds required for exactly 60 cubic low viscosityindex,it signifies a relatively large change of
centimeters of oil to fiow through anaccurately calibrated viscosity of increasedtemperature. The oil becomes thin at
high temperatures and thick at low temperatures. Oils with
orificeis recorded as ameasure ofthe oil"'sviscosity)Ifactual a high viscosityindex have small changes in viscosity over
Saybolt values were used to designate the viscosity of oil,
a wide temperature range.
there would probably be several hundred grades of oil.

To simplify the selection of oils, they are often classified Thebest oil for most purposes is one that maintains a cOnstalnt
viscosity throughouttemperature changes. Oil having a high
underan SAE systemthat dividesall oilsintoseven groups viscosity index resists excessivethickeningwhen the engine
(SAE 10 to 70) according to viscosity at either 130 °F or
is subjected to cold temperatures. This allows for rapid
210 9E. SAE ratings are purely arbitrary and bear no direct
cranking speeds during starting and prompt oil circulation
relationship to the Saybolt or other ratings.
during initial start up. This oil resists excessive thinning
when the engine is
The letter Woccasionally is included inthe SAE number full lubrication and bearingat operating temperature and provides
load protection.
giving adesignation.such as SAE 20W. This Windicates
thattheoil,in additiontomeetingthe viscosityrequirements Flash Polnt and Fire Point
at thetestinggtemperature specifications,i_ satisfactory oil. Flash point and fire point are determined by laboratory tests
P forwithwinter useincold climates. This should not be confused that show the temperature at which a liquid begins to give
the Wused in front
of the grade or weignt numer off ignitable vapors, flash, and the temperature
indicates the oil is of the ashless dispersanttype. at which there_ ¥
are sufficient vapors to support a flame, fire, These points
are established for engine oils to determine that they can
Although the SAE scale has eliminated some confusion in
withstand the high temperatures encountered in an engine.
tne designation of lubricating oils, it must not be assumed
that this specification covers all the important
VISCOSIy
equirements. An SAE numberindicates only the viscosity
Cloud Point and Pour Point

"grade or relative viscosity; it does not indicat ua Cloud point and pour point also help to indicate suitability.
The cloud point of oil is the temperature at which its wax
er essentialcharacteristics. It is well known that there are
Od oils and inferior oils that have the same viscosities at a content,
separate
normlly heldin solution bepinsto solidifyand XA
into tiny crystals, causing the oil to appear clOuay
en temperaure and, therefore, subject
in the same
are to classification
grade. Orwhich
hazy. The pour point.ofoil isthelowesttemperature at
it flows or can
be poured.

6-3
 Some multigrade 0il 1s a blend of
Specific Gravity syntheuc and
efert mineral.
eral
Pased oil semisynthetic, plus a highly
comparison of the weight of the ve
Specific gravity is a of distilled water package,
that is added due to concern that
fully synthetic oit
an equal volume
Substance tothe weight of may not have the solvency to handle the lead deposits that
temperature As an example, water weighs
A a specified result from the use of leaded fuel. As multigrade oil, it
oil with a specific offers
approximately 8 pounds to the gallon; the flexibility to lubricate effectively over a wider rangec
gallon.
gravity of 0.9 would weigh 7.2 pounds to the temperatures than monograde 0ils. Compared to monograde
orot
In the early years, the performance of
aircraft piston engines 011, multigrade oilprovidesbetter cold-starttvnical
stronger lubricantfilm (higher viscosity) at
Was such that they could be
lubricated satisfactorily by means
he combination of nonmetalliC.nt
selected temperaturesI
of straight mineral oils, blended from specially addiuves and selected high viscosity index miner
and
petroleum base stocks. Oil grades 65,80, 100, and 120 are synthetic base oils give exceptional stability, disrerc.
selected high-viscosity sancy,
Straight mineral oils blended from and antifoaming performance. Start up can contrihite up tu
oils do not contain any additives except
indexbaseoils. These buhrio
forvery small amounts of pour point depressant,
which helps 80 percent of normal engine wear due to lackof
during the start-up cycle. The more easily the oil flows t
and an antioxidant.
improve fuidity at very low temperatures, the engine's components at start up, the less wear occurs.
This of oil is used during
type the break-in period of a new
aviation piston engine or those recently overhauled. The ashless dispersant grades are recommended for aircraft
engines subjected to wide variations of ambient temperatiree,
Demand for oils with higherdegrees ofthermal and oxidation
them with the addition of paticularly the turbocharged series engines that require oil
stability necessitated fortifying to activate the various turbo controllers(At temperatures
Small quantities of nonpetroleum materials. The first additives
engine and oil supply tank is
incorporatedinstraight mineral piston engine oils were based below 20 Epreheating of theof the type of oil used
on the metaliesalts.of barium and calcium. In
most engines, normally required regardless
the performance of these oils with respect to oxidation and
thermal stability was excellent, but the combustion chambers Premium, semisynthetic multigrade ashless dispersant oil is
of the majority of engines could not tolerate the presence of the a special blend of a high-quality mineral oil and syntheúic
ash deposits derived from these metal-containing additives. To hydrocarbons with an advanced additive package that has
overcome the disadvantages of harmful combustion chamber been specifically formulated for multigrade applications.
a nonmetallic (i.e., non-ash forming, polymeric) The ashless antiwear additive provides exceptional wear
deposits,
additive was developed that was incorporated in blends of protection for wearing surfaces.
selected mineral oilbase stocks.(W oils are of the ashless
ype andarestillinuseyThe ashlessdispersant gradescontain Many aircraft manufacturers add approved preservative
additives, one of which has a viscosity stabilizing effect lubricating oilto protect new enginesfrom rust and corrosion
that removes the tendency of the oilto thin out at high oil atthetimetheaircraftleavesthe factory. This preservative ol
temperaturesand thicken at low oil temperatures.) shouldbe removed at end of the first 25 hours of operation.
When adding oil during the period when preservative ol i5
The additives, in these oils extend operating temperature in the engine, use only aviation grade straight mineral oil lor
range and improve cold engine startingand lubrication of ashless dispersant oil, as required, of the viscosity desired.
the engine during the critical warm-up period permitting
fight through wider ranges of climatic changes without the Ifashlessdispersantoil is used in a new engine,ora newly
necessity of changing oil. r
overhauled engine, high oil consumpionmight possiblybe
éxperienced. The additives in some of these ashless dispersant
Semi-synthetic multigrade SAE W15 W50 oil for piston oils may retard the break in of the piston rings and cyi
engines has been in use for some time. Oils W80, W100, walls. This condition can be avoided by the use of minera
and W120 are ashless dispersant oils specifically developed oil until normal oil consumption is obtained, then change o
for aviation piston engines. They combine nonmetallic the ashless dispersant oil. Mineral oil should also be u
additives with selected high viscosity index base oils to
following the replacement of one or more cylinders or un
give exceptional stability, dispersancy, and antifoaming the oil consumption has stabilized.
performance.(Dispersancy is the ability of the oil to hold
particles in suspensIon unul they can either betrapPped by In all cases, refer to the manufacturers' information w noil
thefilter or drained at the next oil change.The dispersancy type or time in service is being considered.
additive is not a detergent and does not clean previously
formed deposits from the interior of the engine.

6-4
 Reciprocating Engine Lubrication systemi scarried in a tank. A pressure pump_circulates ne
Systems oilthrough the engine. Scavenger pumps then return it to the
Aircraft reciprocating engine pressure lubrication systems lank as quickly as it accumulates in the engine sumps. The
an be divided into two basic classifications: wet sump
car
need for a separate supply tank is apparent when considering
dry and that would resultif large quantities of oil
sump system werecomplications
the
dry sump.
1he main difference is
that the wet
ores oil in a reservoir inside the engine. After the oil isS
Sto
carried in the engine crankcaselOnmultiengineaircraft
irculated through the engine, it is returned to this crankcase- each engine is supplied with oil from its own complete and
hased reservoir. A
dry sump engine pumps the oil from the independent system.
engine's Crankcase tO an extermal tank that stores the oil.
The dry sump system uses a Scavenge pump, some Although he arrangement of the oil systems in different
tubing, and an external tank to store the oil. external aircraft varies widely and the units of which they are composed
differ in construction details, the functions of all such systems
other than this difference, the systems use similar types of are the same. A study of one system clarifies the general
nponents. Because the
dry sump system operation and maintenance requirements of other systems.
components of the wet sump system, the drycontains all the
sump system
isexplained as an example system. The principal units in a typical reciprocating engine dry
sump oil system include an oil supplytank, an engine-driven
Combination Splash and Pressure Lubrication pressure oil pump, a scavenge pump, an oil cooler with an
The lubricating oil is distributed to oil cooler control valve, oil tank vent, necessarytubing, and
the various moving parts
ofa typicalinternal combustion engine by one of the three PresSure andtemperature indicators. [Figure 6-4
following methods: pressure, splash, or a combination of
pressure and splash. Oil Tankss

The pressure lubrication system is the principal method of

Oil tanks are generally
associated with adry sump lubrication
system, while a wet sump system uses the crankcase of the
lubricating aircraft engines. Splash lubrication may be used engine to store the oi. Oil tanks are usually constructed of
in addition to pressure Iubrication on aircraftengines, but it aluminum alloy and must withstand any vibration,inertia,
is never used by itself; aircraft-engine lubrication systems are and fluid loads expected in operation.
always either the pressure type or the combination pressure
and splash type, usually the latter Each oil tank used with a reciprocating engine must have
expansion space of not less than the greater of 10 percent
The advantages of pressure lubrication are: of the tank capacity or 0.5gallons. Fach filler cap of an oil
=
tank that is used with an engine must provide an oil-tight
Positive introduction of oil to the bearings. seal. The oil tank usually is placed close to the engine and

Cooling effectcaused bythe large quantities of oil higheñough abovetheoil pump inlet toensuregravity feed.
that can be pumped, or circulated,througha bearing.
Oil tank capacity varies with the different
Satisfactory lubrication in various attitudes of fight. types of aircraft,
but it is usually sufficient to ensure an
adequate supply of
oil for the total fuel supply. The tank filler neck is
Lubrication System Requirements positioned
The lubrication system of the engine must be designed and
to provide sufficient room for oil expansion and for foam
to collect.
constructed so that it functions properly
within all flight
attitudes and atmospheric conditions that the aircrart 1s (The filler cap.or.cover is
Cxpected to operate. In wet sump engines, this requirement in marked with the word OLA drain
must be met when only half of the maximum lubricant supply
the filler cap well disposes of
any overfiow caused by the
filling operation. Oil tank vent lines are provided to ensure
1S in the engine. The lubrication system of the engine must proper tank ventilation in all attitudes
be designed and constructed to allow installing a means of
of fight. These lines
are usually connected to the engine crankcase to prevent the
cooling the lubricant. The crankcase must also be vented to loss of oil through the vents. This
uneatmosphere to preclude leakage of oil from excessive to the atmosphere
indirectdy vents the tanks
through the crankcase breather.
pressure
Early large radial engines had many gallons of oil in their
Wy Sump Oll Systems tank. To help with engine warm
Many reciprocating and turbine aircraft engines havepressure up, some oil tanks had a built-
in
hopper or temperature accelerating well. [Figure 6-5]This
Y Sump lubrication systems. The oil supply in this type of well extended from the oilreturn fitting on top of the oil
tank

6-5
 Supply Engine breather
Pressure

Vent

Retum

Drain

Ol pressure gauge Scavenger pump

Oil
Oil
Press.
Temp

Oil coole Oil pressure pump

Oil
Oil
Temp
Press. Oltank vent
wwwo

Ol temperature gaue
Oltank

Scupper drain
*r0w*******
Flexible weighted internal hose assembly
Ol tank drain valve

Figure 6-4. Oil system schematic.

The opening at the bottom of the hopper in one type and

the flapper valve-controlled openings in the other allow dil
from the main tank to enter the hopper and replace the oil
consumed by the engine.(Whenever the hopper tank includes
theflapper controlled openings, the valves are operated by
differential oil pressureBy separating the circulating oil from
the surrounding oil in the tank, less oil is circulated. This
hastens the warming of the oil when the engine was started
Veryfew ofthese typesoftanks aresillinuse andmostare
associated with radial engine installations.

Generally, thereturn line in thetop ofthetank is positioned

Hopper tank todischargethereturned oil against the wallofthetankina
swirlingmotion.This methodconsiderablyreducesfoaming
that occurs when oil mixes with air. Baffles in the bottom
of the oil tank break up this swirling action to prevent air
from being drawninto theinletline of theoil pressure pump
Bafle Foaming oil increases in volume and reduces its ability to
provide proper lubrication. In the case of oil-controlled
propellers, the main outlet from the tank may be in the form
Figure 6-5. Oil tank with hopper.
of a standpipe so that there is always a reservesupplyo
to the outlet fitting inthe sumpin thebottom ofthe tank. In tank
oil forsump,
propellerfeatheringincase of engine failure, Anou
attached to the undersurface of the tank, acts as
some systems, the
hoppertankjsopentothemainoil supply 6-4) The water an
at the lower end. Other systems have flaper-type valves trap for moisture and sediment. (Figure
that separate the main oil supply from the oil in the hopper.

6-6
 sludge can be drained by
in the bottom of the sump.
manually opening the drain valve As oil enters the gear chamber, it is picked up by the gear
tceth, trapped between them and the sides of the gear
chamber, is carried around the outside of the gears, and
Most aircrart oll systems are
equipped with the dipstick-type discharged from the pressure port into the oil screen pas5a
quantity gauge, olen caled a bayonet gauge.
aireraft sysems aiso nave an
oil quantity
Some larger The pressurized oil flows to the oil filter, where any solia
that showsthe
quantity of oil during indicating system particles suspended in the oil are separated from it, prevenung
eonsistsessentially of an arm and floatflight. One type system possible damage to moving parts of the engine.
the level oI e O ana mechanism that
actuates an electric transmitter onrides
of the tank. 1ne top Oil under pressure
ransmitter is connected to a cockpit gauge then opens the nier Cn
that indicates the quantity of oil mounted in the top of the filter. Thisoil valve 1s usea
With dry sump radial mosy
engines and is closed by alight spring
Oil Pump loading of 1to 3 pounds per square inch (psi) when the engine
Oil entering the engine is 1s not operating to
prevent gravity-fed oil from entering
pressurized, filtered, and regulated the engine and settling in the lower
by units within the engine. They are cylinders or suP
discussed along with of the
the external oil system to provide a engine. If oil were allowed to gradually seep y u
concept of the complete rings of the
oil system. piston and fill the combustion chamber, it
cause a liquid lock. This could cou
happen if the valves on the
CAs oil enters the engine, it is cylinder were both closed and the engine was cranked for
Dump) fFigure 6-6] This pump is a pressurized by a gear-typ start. Damage could occur to the engine.
positive
pump that consists ot two meshed gears that revolvedisplacement
thehousing. clearance between the teeth and insideis The oil filter bypass valve, located between the pressure siae
The
small. The pump inlet is located on the left and thehousing of the oil pump_ and the oil filter, permits
unfiltered
is discharge
port connected to the engine's system pressure line. One bypass the filter and enter the engine if the oil filter is oil to.
or during cold weather if congealed oil is blocking the clOggea
gear is attached to a splined drive shaft that extends filter
the pump housing to an accessory drive shaft on the from during engine start. The spring loading on the bypass valve
Seals are used to prevent leakage around the drive shaft. engine. allows the valve to open before the oil
pressure collapses
As the filter; in the case of cold,
the lower gear is rotated
counterclockwise, the driven idler low-resistance path around the filter. congealed oil, it provides a
gear turns clockwise. Dirty oil in an engine
is better than no lubrication.
wwwww..aam

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Relief yalve wwww.
Oil pressure passage to engine
wwwwwwww.wAWAwMKAWw

DaSS

Ol vave

Oll filter
wwwww.w.wwwwww..

Gear-typeoll pump

igure &-4. Engine oil purmp and associated units.

6-7
 Oil Filters
cThe oil filter used on an aircraft engine is usually oneof four_
AVpes.SCreen. Cuno. canister, orspin-on. A screen-type filler Hex head scrøw
with its double-walled construction provides a large filtering
the
areain a compact unit /Figure 6-6] As oil passes through
fine-meshscreen,dirt, sediment, and othe foreign matterare
removed and settle to the bottom of the housing. At regular
******ev
ntervals, the cover is removed and the screen and housing Gopper gasket
cleaned with a solvent. Oil screen filters are used mostly as
suctionfilters on theinlet of the oilpump. AX Case housing or canister
TheCunooilfilter has acartridgemade of disks and spacers.
A cieanerblade fits betweeneach pair of disks. The cleaner
blades are statianary. but the disks rotate when the shaft
that
IS turned.Oil from the pump enters the cartridge well Filter elemern
surrounds the cartridge and passes through the spaces
between the closely spaced disks of the cartridge. then
ww
through the hollow center, and on to the engine. Any foreign *****Vwww www.
Rubber gasket
particles in the oil are deposited on the outer surface of the
wwwe

Cover plate
*********www

cartridge. When the cartridge is rotated, the cleaner blades

comb the foreign matter from the disks.
Thecartridge ofthe *****
MUbber gasket
manually operated Cunofilter isturmedby anexternal handle.
Automatie Cuno filters have a hydraulic motor built into wwwwww.wwww.www.www.ewwwwwwwwwa
Nylon nut
thefilter head. This nmotor, operated by engine oil pressure,
rotates the cartridge whenever the engine is running There is
a manual turning nut on the automatic Cuno filter for rotating Figure 6-7. Housing filter element type oil filter.
the cartridge manually during inspections. This filter is not
often used on modern aircraft.

A canister housing filter has a replaceable filter element

that is replaced with rest of the
components other than
seals and gaskets being reused. [Figure 6-7] The filter
element is designed with a
corrugated, strong steel center
tubesupporting each convoluted pleat of the filter media, CHAMION
resulting in a higher collapse pressure rating. The filter
provides excellent filtration because the oil flows through
many layers Ol locked-in-fibers,
Full flow spin-on filters are the most widely used oilfilters
for reciprocating engines. [Figure 6-8]
Full flow means that
allthe oil is normally passed through the filter. In afull low
system, the filter is positioned between the oil pump and the
Figure 6-8. Full flow spin-on filter.
engine bearings, which filters the oil of any contaminants
before they pass through the engine bearing surfaces. The Oil Pressure Regulating Valve
niter also contains an antidrain back valve and a pressure An oil pressure regulating valve limits oil pressureto
TCHer valve, all sealed in a disposable housing. The relief a predetermined value, depending on the installation
valve is used in case the filter becomes Figure 6-6] This valve is sometimes referred to as a relier
clogged. It would open
tO allow the oil to bypass, preventing the engine components valve but its real function is to regulatetheoil pressuirea
rom oil starvation. A cutaway of the micronic filter element present pressure level.The oil pressure must be suinci
Shows the resin-impregnatedcellulosicfull-pleat mediathat high to ensure adequate lubrication of the engine An
s usedtotrap harmfulparticles. keepingthemfrom entering accessories at high speeds and powers. hspressu
the engine. [Figure 6-9) ensure that the oil film between theerankshatt journalna 7
the pressure must not be to0
Dearingis maintaind. However,

6-8
 Satety wire tabs
on hex nut for convenlently
easy acce96 located

Resin-impregnated,
cellulosic full-pleat
Corrugated center support tube for medla for uniform
maximumrosisuance-to cotapee tow and collapse
esistance

Figure 6-9. Cutaway view of a filter.

high, as leakage and damage to the oil system

is may result. The
oil pressure generally adjusted by loosening the
and turning the adjusting locknut
screw. [Figure 6-10] On most Figure 6-10. Oil pressure adjustment screw.
aircraft engines, turning the screw clockwise
increases the
tension of the spring that holds the relief valve on its seat too violently with each pressure pulsation. The oil pressure
and increases the oil pressure; turning the adjusting screw gauge has ascale ranging from0-200 psi. or from 0-300 psi. X
counterclockwise decreases the spring tension lowers Operation range markings are placed on the cover glass, or
thepressure. Some engines use washers under theand spring that the face of the gauge, to indicate the safe
range of oil pressure
are either removed or added to for a given installation.
adjust the regulating valve
and pressure. The oil pressure should be adjusted only after
X the engine's oil is at operating temperature and the correct A dual-type oil pressure gauge is available for use
on
ViscOSity is verified. The exact procedure for adjusting the oil engine airerart.
The
dual indicator contains two Bourdon
pressure and the factors that vary an oil pressure setting are tubes,housed in a standard instrument case; one tube being
included in applicable manufacturer's instructions. usedfor each engine. The connections extend from the back
of the case to each engine. There is one common movement
Oll Pressure Gauge assembly, but the moving parts function independently. In
Usually, the oil pressure gauge indicates the pressure that oil Sme installations, the line leading from the engine to the

enters the engine from the pump. This gauge warns of possible pressure gauge is filled with light oil. Since the viscosity
of this oil does not vary much with
engine failure caused by an exhausted oil supply, failure of changes in temperature,
the gauge responds better to changes in oil
ne oil pump, burned-out bearings, ruptured oil lines, or other pressure. In time,
causes that may be indicated
engine oil mixes with some of the light oil in the line to the
by a loss of oil pressure.
transmitter; during cold weather, the thicker mixture causes
e type of oil pressure gauge uses a Bourdon-tube EES nstrunment readings. To correct this condition, the
gauge line must be disconnected, drained, and refilled with
echanism that measures the difference between oi light oil.
re and cabiF, or atmospheric, pressure. This gauge is
Onstructed similarly to other Bourdon-type gauges, except The current trend is toward electrical transmitiers and
Uhat it has a small restriction builtinto theinstrument case,
indicators for oil and fuel pressure-indicating
systenns in all
T hE nipple connection leading to the Bourdon tube. aircraft. In this type of indicating system, the oil pressure
restriction prevents the surgingaction of the oil pump being measured is applied to the inlet port of the electrical
romdamaging the gauge orcausing the pointerto oSC1llate
6-9
 transmilter where it is conducted to a diaphragm ussembly The space between the inneT and oulcr shells is known a
theaunular or bypuss jacket.)! wo paths are opento theflow
byacapillarytube.Themotionproducedbythe diaphragm's
and through a cooler. I'Tom the inlel, it can flow halfwau
of oil
CXpansion and contraction isamplitied through a lever
the bypass jacket, enter the core from the bottom
Ar AITANgement. The gear varies the clectrical value of thearound and then pass through the spaces between the tubes and ou
indicating circuit, which in turn, is rellected on the indicator in to the oil tank. This is the path the oil follows when it is hot
Lhe.cockpit. This type of indicating system replaces long fluid- enough to require cooling. As the oil flows through the core.
filled tubing lines with an almost weightless piece of wire.
it is guided by baffles that force the oil to travel back And
forth several times betlore it reaches the core outlet. The oil
Oll Temperature Indicator
n dry-sump Jubricating systems, the oil temperature bulb can also pass from the inlet completely around the bypass
jacket to the outlet without passing through the core. Oil
ymay be anywhere in the oil inlet line betwecn the supPY
follows this bypass route when the oil is cold or when the
tank andthe engine. Oil systemsfor wel-sump.engines have core is blocked with tlhick, congealed oil.
ethe temperaturebulblocatedwhere it senses oiltemperature
In either the
after theoilpasses throughiheoil.cooler. system,
Oll Cooler Flow Control Valve
bulb is located so that it measures the temperature of the oil
before it enters the engine's hot sections. An oil temperature As discussed previously, the viscosity of the oil varies with
gauge in the cockpit is connected to the oil temperature bulb its temperature. Since the viscosity affects its lubricating
by electrical leads. The oil temperature is indicated on the properties, the temperature at which the oil enters an engine
gauge. Any malfunction of the oil cooling system appears must be held within close limits. Generally, the oil leaving
as an abnormal reading. an engine must be cooled before it is recirculated. Obviously,
theamountofcoolingmustbe.controllediftheoilis to retun
Oil Cooleer tothe engine atthe correcttemperature.The oilcooler flow
The çooler,cithercylindiaicaloreliptical shaped consiss controlvalve determineswhichofthetwopossible pathsthe
through the oil cooler. /Figure 6-12]
The is built
OTa core enclosed ina double-walled shell. core oil takes
with the tube ends formed to
of copper or aluminum tubes
a hexagonalshape and joined together in the honeycomb Therearetwoopeningsina flowcontrol valvethatfit overthe
effect. [Figure 6-11] The ends of the copper tubes of the correspondingoutlets at the topof the cooler. When the oil
core are soldered, whereas aluminum tubes ar brazed or is cold, a bellows within the fow control contracts and lifts
mechanically joined. The tubes touch only at the ends so a valve from its seat. Under this condition, oil entering the
that a spacee exists between them along most of their lengths. cooler has a choice of two outlets and two paths. Following
This allows oil to flow through the spacesbetween the tubes the path of least resistance, theoilflows around the jacket
while the coolingair passes through the tubes. X andout pastthe thermostatie valve to the tank. This allows
theoil to warm up quickly and, at the sametime, heatsthe x
Outletfrom bypass jaoket
oilinthe core.Asthe oil warmsup and reachesits operating
Inletfrom engine temperature, the bellowsof the thermostat expand and closes
the outlet from the bypass jacket. The oil cooler flow control
valve, located on theoilcooler,mustnowflow oilthroughthe.
Baftles core ofthe oilcooler. No matter which path it takes through
the cooler, the oil always flows over the bellows of the

Outlet from core

thermostatic valve. As the name implies, this unit regulates
the temperature by either cooling the oil or passing it on to
the tank without cooling, depending on the temperature at
which it leaves the engine.

Surge Protection Valves

When oil in the system is congealed, the scavenger pump.
To
may build up a very high pressure in the oil return lin.
Prevent this high pressure from bursting the oil coaler or.
blowing off the hose connections, some aircraft have surge
*
Bypass jacket Core protection valves in the engine lubricationsystems(One type.
ofsurge valve is incorporated in oil cooler flow
the control
valve another typeis a separate unit in the oil return line.
Figure 6-11. Oll caoler. IFigure 6-12]

6-10
 Surge condition Hot oil low
Cold oll flow

Control valve outlet Surge valye Poppet valve Core outet

Check vave Control valva inlet Bypase jacket Bypass jacketoutlet
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Flgure 6-12. Control valve with surge protection.

The surge protection valve incorporated in a flow control One of the most widely used automatic oil temperature
valve is the more common type. Although this fow control control devices is the floating control thermostat that provides
valve differs from the one just described, it is essentially manual and automatic control of the oil inlet temperatures.
the same except for the surge protection feature. The
high- With this type of control, the oil cooler air-exit door 1s
pressure operation condition is shown in Figure 6-12, in opened and closed automatically theanactuator
which the high oil pressure at the control valve inlet has actuator. Automatic operation ofby electrically operated
is determined
forced the sürge valve (C) upward. Note how this movement by electrical impulses received from a controlling thermostat
has opened the surge valve and, at the same time, seated inserted in the oil pipe leading from the oil cooler to the oil
the poppet valve (E). The closed poppet valve prevents oil supply tank. The actuator may be operated manually by an
from entering the cooler proper, therefore, the scavenge oil oil cooler air-exit door control switch. Placing this switch in
passes directly to the tank through outlet (A) without passing the
"open" or "closed" position produces a corresponding
through either the cooler bypass jacket or the core. When the movement of thecoolerdoor.Placing the switchinthe"auto"
pressure drops to a safe value, the spring forces the surge and
pOsition puts the actuator underthe automatic controlofthe
poppet valves downward, closing the surge valve (C) and fioating control thermostat. [Figure 6-13] The thermostat
opening the poppet valve (E). Oil then passes from the control shown in Figure 6-13 is adjusted to maintain a normal oil
valve inlet (D), through the open poppet valve, and into the temperature so that itdoes not vary more than approximately
bypass jacket (F). The thermostatic valve, according to oil S to8C.depending on theinstallation.
temperature, determines oil flow either through the bypass
jacket to port (H) or through the core to port (G). The check During operation, the temperature of the engine oil fowing
valve (B) opens to allow the oil to reach the tank return line. over the bimetal element causes it to wind or unwind slightly.
Figure 6-13B] This movement rotates the shaft (A) and the
Airfiow Controls grounded center contact arm (C). As the grounded contact
By regulating the airflow through the cooler, the temperature arm is rotated, it is moved toward either the open or closed
of the oil can be controlled to fit various operating conditions. floating contact arm (G). The two floating contact arms are
For example, the oil reaches operating temperature more oSCillated by the cam (F), which is continuously rotated by
quickly if the airfiow is cut off during engine warm-up. There an electric motor (D) through a gear train (E). When the
aretwo methodsin general use: shuttersinstalledontherear grounded center contact arm is positioned by the bimetal
of theoilcooler, and a flap on theair-exitduct. In some cases, element so that it touches one of the floating contact arms,
the oilcooler air-exit flap is openedmanually and closed by an eleciric circuit to the oil cooler exit-fap actuator motor is
a linkage attachedto a cockpit lever. More often, the flap is completed, causing the actuator to operate and position the

opened and closed by an electric motor *

6-11
 wAMRANRAlNtAAena ANwAAM AAA

Top view

Shaft
Bimetal element
Grounded center contact am
Electric motor
GearGear train
SideVviewW
am
Floating contact arm

Figure 6-13. Floating control thermostat.

oil cooler air-exit flap. Newer systems use electronic control cooler and flow regulatorjust described. Oil from the coolers is
systems, but the function or the overall operation is basically routed through two tubes (D) to a Y-fitting, where the
the same regarding control of the oil floating
temperature through control thermostat (A) samples oil temperature and
positions
control of the air flow through the cooler. the two oil cooler air-exit doors through the use of a
two-door
actuating mechanism. From the Y-fitting, the lubricating oil
In some lubrication
systems, dual oil coolers are used. If the is returned to the tank where it
completes its circuit.
typical oil system previously described is adapted to two oil
coolers, the system is modified to include aflow divider,
two Dry Sump Lubrication System Operation
identical coolers and flow regulators, dual air-exit doors, a The following
lubrication system is typical of those on small,
two-dooractuating mechanism, and a Y-fiting [Figure 6-14] single-engine aircraft.
Oil is returned from the The oil system and components are
engine through a single tube to the those used to
flow divider (E), where the returm oil ffow is
divided equally
lubricate a 225 horsepower (hp) six-cylinder,
into two tubes (C), one for each cooler. The
coolers and
horizontally opposed, air-cooled engine. In atypical dry sump
regulators have the same construction and pressure-lubrication system, a mechanical pump supplies
operations
as the
oil under pressure to the
bearings throughout the engine.
[Figure 6-4] The oil fows into the inlet or suction
the oil pump through a suction screen and aline side of
connected to
theexternal tank at a point higher than the bottom of the oil
Sump. This
prevents sediment that falls into the sump from
being drawn into the pump. The tank outlet is
the pump inlet, so higher than
gravity can assist the flow into the pump.
The engine-driven, positive-displacement,
gear-type pump
forces the oil into the full flow filter. [Figure 6-6] The oil *
either passes through the filter under normal conditions or,
ifthe filter were to become clogged, the
flter bypass vaiv
WOuld open as mentioned earlier. In the bypass
oil would not be filtered. As position, the
seen in Figure 6-6, the
(relief) valve senses when regulating
system pressure is reached and
Floating control thermostat opens enough to bypass oil to the inlet side of the oil pump
Outlet from cooler tubes
Then, the oil fows into a manifold that distributes
Y-iting Flow divider through drilled passages to the crankshaft bearings andthe ol
iniet to cooler tubes Dearings throughout the other
engine. Oil flows from the main
**

bearings through holes drilled in the crankshaft to the

Flgure 6-14. Dual oil cooler system. connecting rod bearings. [Figure 6-15} lower

6-12
 Camshaft bearing
Camshaft bearing

Jdler shaftbushing
To propeler
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Accessory drive bushing

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Fligure &-15. Oil circulation through the engine.

Oil reaches a hollow camshaft(in an inline or opposed collected in these sumps ispicked upby gear orgerotor-type
engine), or a cam plate or cam drum (in a radial engine). scavengerpumps as quicklyasitaccumulates. These pumps
through a connection with the end bearing or the main oil havea greater capacity thanthe pressure pump.This is needed
manifold; itthen flows out tothe various camshaft, cam drum, because the volume of the oil has generally increased due
to foaming (mixing with air). On drysump engines, this oil
orcam plate bearings and thecamns.
leaves the engine, passesthroughthe ollcooler, andreturns
Theengine cyinder surfaces receiveoil sprayed from the tothesupply tank.
Since oil
Crankshaftand also from the crankpin bearings.
seepsslowly throughthesmallcrankpin clearances before it A thermostat attached to the oil cooler çontrols oil
18 6prayed on the cylinder walls, considerable time is required temperatureby allowing part of the oiltofow through the A
forcoldenough oiltoreach thecylinder walls,especially on a coolerand parttoflowdirectlyintotheoil supplytank. This
day when the oil fow is more sluggish. This is one of arrangement allows hot engine oil with a temperature still
thechiefreasons for using modernmultiviscosity oilsthat below 65 °C (150 F) to mix with the cold uncirculated oil
flow well at low in the tank. This raises the complete engine oil supply to
temperatures. operating temperature in a shorter period of time
of
nen the circulating oil has performed its function it
uDricating and cooling the moving parts of the engine,
ns into the sumps in the lowest parts of the engine Oil

6-13
 Wet-Sump Lubrication System Operation Speed of the puinp IrOm idling to full-tirottle.operatine range
A simple form ofa wet-sump system is shown in Figure 6-16. of the engine and the fluctuation of oil viscositybecauseo
temperature changes are compensatcd by thetensionon the
he systeinsonsists ofa sump or pan in which the oil supply relief valve spring. The pump is designed to create a greater
iscontaine. The oil suppBy is limited by the sump (otl pan)
Capacty, Ihe level (quantity) of oil is indicated or measured pressure than required to compensate for wear of the bearina
or thinning out ot Oil. Ihe parts oiled by pressure throu.
a vertical rod that protrudes into the oil from an elevated lubricating spray into the cylinder and piston assemblies
hole on top of the crankcase.In the botom of the sump (oil
pan)is ascreen strainer having asuitable mesh. or series of Ater lubricating the _various units it sprays, the
oil draine
and yet back into the sunp and the cycle IS repeated, The system i
openings. to strain undesirable particles from the oil
Pass suthcCient quanity to the inlet or (suction) side of the oil not readily adaptable to inverted flying since the entire oil
floods the engine. K * X
PrEsure pmp Figure 6-17 show <atvpicaloil sump that has supply
the intake tube running through it This preheats the fuel-air
Lubrication System Maintenance
mixture before it entersthe cylinders. )¥* Practices
oil Tank u
The oil tank, constructed of welded aluminum, is serviced
(filled) through a filler neck located on the tank and equipped
Oil fi with a spring-loaded locking cap. Inside
the tank.a weighted,
flexiblerubber oil hose is mounted so that it is repositioned
automatically to ensure oil pickup during all maneuvers. A
dipstick guard is welded inside the tank for the protection
Wet sumb oit system's sump of the flexible oil hose assembly. During normal
flight,
the oil tank is vented to the engine crankcase by a flexible
line at the top of the tank. The location of the oil system
components in relation to each other and to the engine is
shown in Figure 6-18.

Drain plu9 Repair of an oil tank usually requires that the tank be
removedThe removal and installation procedures normally
Figure 6-16. Basic wet-sump oil system.
remain the same regardless of whether the engine is removed
or not.
First, the oil must be drained. Most light aircraft
provide an oil drain similar to that shown in Figure 6-19. On
some aircraft, the normal
ground attitude of the aircraft may
prevent the oil tank from draining completely. fthe amount
of undrained oil is excessive, the aft
portion of the tank can
be raised slightly after the tank have been loosened to
straps
complete the drainage.

After disconnecting the oil inlet and vent lines, the scupper
drain hose and bonding wire can be removed. [Figure 6-20]
The securing straps fitted around the tank can now be
removed. [Figure 6-21]) Any safety wire securing the clamp
must be removed before the clamp can be loosened and the
strap discannected. The tank can now be lifted out of the
aircraft. The tank is reinstalled by
reversing the sequence used
in the tank removal.
Figure 6-17. Wet-sump system's sump with intake tube running After installation, the oil tank should be
filled to capacity.
through i. [Figure 6-22]
After the oil tank has been filled,
The rotation of the pump,
which is driven_by ihe_engne the engine should be nun for
causes the oil to pass around the outside of the gears.
at least twaminutes. Then, the oil level should be.checkea
IFigure 6-6] This develops pressure
a in the crankshaft and,if necessary, sufficient oil should he added to bring the
oil up to the proper level on the
oiling sysem (drilled passage holes). The variation in the dipstick. [Figure 6-2

6-14
 Figure 6-21. Removai of securing straps.
************

Flgure 6-24. Oil cooler.

his valve begins to close when the oil temperature reaches

approximately 65 °C(is0 °F). When the oil temperature
reaches 85°C(185 °F), #2 °C, the valve is closed completely,
diverting all oil flow through the cooler core.
Oil Temperature Bulbs
Most oil temperature bulbs are mounted in the pressure oil
screen housing. They relay an indication of engine oil inlet
Figure 6-22. Filling an oil tank.
to the oil
temperature temperature indicators mounted on
the instrument panel. Temperature bulbs can be replaced by
removing the safety wire and disconnecting the wire leads
from the temperature bulbs, then
removing the temperature
bulbs using the proper wrench.
[Figure 6-25]
Pressure and Scavenge Oll Screens
Sludge accumulates on the pressure and scavenges oil screens
during engine operation. [Figure 6-26] These screens must
be removed, inspected, and cleaned at the intervals specified
by the manufacturer.

Typical removal procedures include removing the safety

devices and loosening the oil screen housing or cover plate.
A suitable container should be provided to.callect the ojl that
drains from the filter housing or cavity. The container must
be clean so that the oil collected in it can be examined for

Figure 6-23. Checking oil level with dipstick.

foreign particles. Any contamination already present in ne
Container gives a false indication of the engine condition.
Oil Cooler This could result in a premature engine removal.
The oil cooler used
i s the honeycomb with
ype.this aircraft's
/Figure 6-24/oppOsed-type engine
With the engine for contamination
After and removed,
the screens are for the presence of metal
they should pauuected Y
be inspoe
operating and an oil temperature below 65C050F), oil that
cooler may indicate possible engine internal wear, aa
bypass valve opens alloWing oil to bypass the core. Or in extreme cases, engine failure. The screen must be

6-16
 Oil Pressure Relief Valve
t
valve limits nl pressure
An oil pressureregulating (reiief)
nanufacturer.il pressure
the value specified hy the engine
fron around 35 psi minimurn to
arund9 . F
etings can vary The oil pressure
installation.
pSimaximum, depending the
on
lubrication of the
must be high enough to ensure adequate
settings.
engine at hizh speeds and power since
and accessories
On the other hand, the pressure mustnos be too higb,
result. Before any
eakage and damageto the oil system may must be
the engine
attempt is made to adjust the oil pressure,
a check should
be
at the correct operating temperature and
in
made to that the correct
assure viscosity oil is being used
the oil pressure is done
One example of adjusting
the engine.

by removing a cover nut, loosening a iocknut, and turming

the adjusting screw. /Figure 6-27] Turn the adjusting sctew
clockwise to increase the pressure, or counterclockwise
to decrease the pressure. Make the pressure adjustments
while the engine is idling and tighten the adjustment screw
Figure 6-25. Removing oil temperature bulb. lock-nut after each adjustment. Check the oil pressure
reading while the engine is running at the rpm specihed in
cleaned prior to reinstalling in the engine. In some cases, the manufacturer's maintenance manual. This m4y De
t 5 ecesary lo disassemble the fiter for inspection and around 1900rpmto 2.300 1pm.The oil pressure reading *
cleaning. ne manuracturer's procedures should be followed should be between the limits prescribed by the manufacturer
when disassembling and
reassembling an oil screen assembly. at all throttle settings.
When reinstalling a filter or screen,
use new O-rings and
gaskeis andüghtentheflter housing or coverreLainingnuts Recommendations for Changing Oil
T to the torque value specified in the applicable maintenance
manual. Filters should be safetied as required. Draining Oil
Oil, in service, is constantly exposed to many harmful
substances that reduce its ability to protect moving parts.

gure 6-26. Oil pressure screen (A) and scavenge oil screen assembly (B).

6-17
 4 All urbocharged engines must be broken in and
operated with ashless dispersant
oil.
Oil and FIlter Change and Screen Cleaning
One manufacturer recommends that for new,
remanufactured:
or newly overhauled engines and for engines with any newlyv
Decrease installed cylinders, the oil should be changed after the first
replacement/screen cleaning at 25 hours. The oil should be
increase changed, filter replaced or pressure screen cleaned, and oil
sump suction screen cleaned and inspected. A
typical interval
for oil change is 25 hours, along with a pressure screen
cleaning and oil sump suction screen check for all engines
employing apressure screen system. 1ypical 50-hour interval
oil changes generally include the oil filter
Figure 6-27. Oil pressure relief vaBve adjustment. replacement and
suction screen check for all engines using full-ffow filtration
The main contaminants are: systems. A time maximum of 4 months between servicing is
alsorecommended for oil system service. *
.Gasoline
Moisture Oil Filter Removal Canister Type
Housing
Acids Remove the filter housing from the engine by
removing the
Dirt
safety wire and loosening the hex head screw and housing
by turning counterclockwise and removing the filter from
Carbon the engine. [Figure 6-7] Remove the
nylon nut that holds
Metallic particles the coverplate on the engine side of the filter. Remove the
cover plate, hex head screw from the housing. Toremove the
Because of the accumulation of these harmful substances, spin-ontype of filter, cut the safety wire and use the wrench
common practice is to drain the entire lubrication system at pad on the rear of the filter to turn the filter counterclockwise,
regular intervals and refill with new oil. The time between and remove filter. Inspect the filter element as described in
N
oil changes varies with each make and model aircraft and the rollowing paragraph. Discard old gaskets and replace
engine combination. with new replacement kit gaskets.
CEn engines that have been operating on straight mineral oil Oil Filter/Screen Content Inspectlon
for several hundred hours, a change to ashless dispersant Check for premature or excessive engine component wear
oil should be made with a degree of caution as the cleaning that is indicated by the presence of metal particles, shavings,
action of some ashless dispersant oils tends to loosen sludge or flakes in the oil filter element or screens. The oil filter
deposits and cause plugged oil passages.When an engine has can be inspected by opening the filter paper element. Check
been operating on straight mineral oil, and is known to be in the condition of the oil from the filter for signs of metal
excessively dirty condition, the switch to ashless dispersant contamination. Then, remove the paper element from the
oilshouldbe defereduntilafterthe engine is overhauled. filter and carefully unfold the paper element; examine the
material trapped inthefilter. If the engine employs a pressure
When changing from straight mineral oil to ashless Screen system, check the screen for metal particles. After
dispersant
oil, the following precautionary steps should be taken: draining the oil, remove the suction screen from the oil sump
and check for metal particles. [Figure 6-28)Ifexamination of
1. Do not add ashless dispersant oil to straight mineral the used oil filter or pressure screen and the oil sump suction
oil. Drain the straight mineral oil from the
engine and
fill with ashless dispersant oil. screen
indicates abnormal metal content, additionalservice
may berequired to determinethe sourceand possibleneedcan
2. Do not operate the engine longer than 5 hours before Corrective maintenance. To inspect the spin on filter the
for
thefirst oil change. must be cut open to remove the filter element for inspection.
3. Check all oil filers and screens for evidence of sludge Using the special filter cutting tool, slightly tighten the
or
plugging. Change oil every 10 hours if sludge Cutter blade against filter and rotate 360° until the mounting
conditions are evident, Repeat 10-hourchecks until plate separates from the can. (Figure 629)Usinga cle
clean screenisnoted.thenchangeoilatrecommended plasticbucketcontaining
ime intervals.
varsol, move thefilier to.renm
Use clean magnet and checkfor any ferous
contaminants. a

6-18
 P

Figure 6-28. Oil sump screen.

metal particles in the filter or varsol solution. Then, take the

Femaining varsol and pour it through a clean filter or shop S

towel. Using a bright hght, inspect for any nonferrous

metals.
Assembly of and Installation of Oil Filters
After cleaning the parts, installation of the canister or filter
element type filter is accomplished
by lightly oiling the new
rubber gaskets and installing a new copper gasket on the e
hex head screw. Assemble the hex head screw into the filter
case using the new copper gasket. Install the filter element
a
and place the cover over the case, then manually thread on
the nylon nut by hand. In_tall the housing on the engine by
y urningitclockwise. thentorque and safetyitlSpin-on fillers
Xfgenerally have installationinstructions on the flter Place a
coating of engine oil on the rubber gasket, install the filter,
torque and safety it. Always follow the manufacturer's
current instructions to perform any maintenance.

Troubleshooting Oil Systems

The outline of malfunctions and their remedies listed in

Figure6-30 can expedite troubleshooting of the lubrication

system. The purpose of this section is to present typical
troubles. It is not intended to imply that any of the troubles
are exactly as they may be in a particular airplane.
 locknut and turn the adjusting screw clockwise to
nterclockwise to decrease, increase, may waste 60 to 70
pressure. Ina typical fuel. Unless most of percent of the original energy in thne
the oil
hojet lubrication system, the adjusting screw is
rurbojet .
fucl. Unless this waste heat is
rapidly
removed,
ide an oil pressure
of 45, 5 psi, at adjusted the cylinders may become hot
to provide
enough to cause
failure. Excessive heat is undesirable in anycomple
ercent of normal rated thrust. The approximately engine failure internal-
be made hile the adjustment
engine idling it may be
is should combustion engine for three principal reasons:
necessary to
oerform several
adjustments before the desired 1. It
affects the behavior of the combustion of the fuel
pressure
obtained. When the proper pressure setting is achieved, air charge.
tighte the adjusting screw locknut, and install
th a new gasket, then tighten and secure withthe acorn cap 2. It
weakens and shortens the life of engine parts.
lock wire. 3.
It impairs lubrication.
of
Maintenance scavenge and breather systems at
nspections includes checks for oil leaks and regular If the temperature inside the
ins security engine cylinder is too greas.
nouning of system components. Also, check chip detectorsof the fuel-air mixture is preheated, and combustion
mou
OCCUs
for narticles of ferrous material and clean last-chance before the desired time. Since premature
install and safety. filters; combustion
detonation, knocking, and other undesirable conaiuons,causes na
must be a way to eliminate heat before it causes damage.
Engine Cooling Systems One gallon of aviation
Excessive heat is always undesirable in both
gasoline has enough heat value to
reciprocating boil 75 gallons of water; thus, it is
and turbine aircraft engines. If easy to see that an engine
means were not available that burns 4 gallons of fuel
per minute releases a tremendous
for its control or elimination, major damage
engine failure would Occur.
complete
or
Although the vast majority of
amount of heat. About one-fourth of the heat released is
changed into useful power. The remainder of the heat must
Yreciprocating engines are air conled, some diesel liquid- be dissipated so that it is not destructive to the engine. In a
cooled engines are being made available for light aircraft. typical aircraft powerplant, half of the heat goes out with the
Figure 6-49] In aliquid-cooled engine. around the cylinder exhaust and the other is absorbed by the engine.
Circulating
are water jackets, in which liquid coolant is circulated and oil picks up part of this soaked-in heat and transfers it to the
the coolant takes away the excess heat. The excess heat is airstream through the oil cooler. The engine cooling system
then dissipated by a heat exchanger or radiator using air flow. takes care of the rest. Cooling is amatter of transferring the
Turbine engines use secondary airflow to cool the inside excess heat from the cylinders to the air, but there is more
components and many of the exterior components. tosuch a job than just placing the cylinders in the airstream.
A cylinder on a large engine is roughly the size
of a gallon
jug. Its outer surface, however, is increased by the use of
cooling fins so that it presents a barrel-sized exterior to the
cooling air. Such an arrangement increases the heat transfer
by radiation. If too much of the cooling fin area is broken off,
the cylinder cannot cool properly, and a hotspot develops
Therefore, eylinders are normally replaced if a specifñed
number of square inches of fins are missing.

Cowling and hafflesaredesignedto forceairoverthecylinder

coolingfins./Figure 6-50] The baffes direct the air close
*
aroundthe ylinders and.prevent it from forming hotpools
of stagnant airwhile the main streamsrush by unused.Blast
tubesare builtinto the bafflesto directjets of cooling air
ontothe rear spark plug elbows of each cylinder to prevent
Figure 8-49. Diesel liquid-cooled aircrafi engine. overheating of ignition leads.

An engine can have an operating temperature that is too low.

Recolprocating Engine Coolling Systems For the same reasons that an engine is warmed up before
An internal-combustion engine is a heat machine that
takeoff, it is kept warm during flight. Fuel evaporation and
cOnverts chemical energy in the fuel into mechanical energy distribution and oil circulation depend on an engine being
at the crankshaft. It does not do this without some loss of
EY, however, and even the most efficient aircraft engines
kept at its optimum operating temperature. The aircraft engine

6-33
 Dete

Figure 6-51. Regulating the cooling airflow.

Air bafi Some aircraft use augmentors to provide additional cooling

airflow. [Figure 6-52] Each nacelle has wo pairs of tubes
running from the engine compartment to the rear of the
nacelle. The exhaust collectors feed exhaust gas into the inner

Pigure &-50 Cyinder bee and deflector system. augmentortubes. The exhaust gas mixes with air that has
passed over the engine and heats it to form a high-temperature,
bas teperaure controls that regulate air circulation over low-pressure.jet-like exhaust. This low-pressure area in the
te engine. Uniess some controis are provided, the engine augmentors drawsadditionalcoolingair over the engine.Air
could overheat on takeoff and get too cold in high altitude, enteringthe outer shells of theaugmentors is heated through
high-speed and low-power letdowns. contact withtheaugmentortubes but is notcontaminatedwith
exhaust gases. The heated air from the shell goestothe cabin
The mostcommon means of controlling coolingistheuse of heating, defrosting,and anti-icing system.
cowi fiaps [Figure 6-51]] These flaps are opened and closed
byelecricmoirdriven jackscrews. by hydraulic actuatos, Augmentors use exhaust gas velocity to cause airfow over
mannaliy in some ight aircraft, When exended for the engine so that cooling is not entirely dependent on the
inceasedcooling, the cowi fiaps produce drag and sacrifice prop wash. Vanes installed in the augmentors control the
volume of air. These vanes are usually left in the trail position
SEanlining for the aidied cooiing.Onakeoff, thecowifiaps
ae opened oniy enough to keep the engine below the red-line to permit maximum fow. They can be closed to increase the
emperature. Heating above the normal range is allowed so heat for cabin or anti-icing use or to prevent the engine from
that drag is as low as possible During ground operations, the cooling too much during descent from altitude. In addition to
owi fiapsshouid be opened widesincedrag does not matter augmentors, some aircraft have residual heat doors or nacelle
and cooiing needs to be set at maximum.Cowl ffaps are used fiaps that are used mainly to let the retained heat escape after
mostiy with oider aircraft and radial engine installations.
engineshutdown. The nacelle flaps can be opened for more
Exhaust gases Cooling air Heated air
Exhaust gas and cooling air mixture

ugmenoo

Figure 6-52. Augmentor.

 that
augmentors. provided by the A modified
coohe
fom of nreviously
described augmentor The cowling performs two functions:
n $ome light aircraft. {Figure cooling system I t streamlines the bulky engine to reduce drag.
s
Used

6-53]
cms are not used much on moderm aircraft. Augmentor
s y s t e m s
Tforms an envelope around the engine that forces air

6-)3, to pass around and between the cylinders, absorbing

n in Figure the engine is pressure cooled by theheat dissipated by the cylinderfins.
AS in through two
airta openings in the nose cowling, one
each.side.n
on
ead Spinner. A pressure chamber is The cylinder bases are metal shields, designed and arranged
1off on the topSIde or the engine with baffles properly to direct the flow of air evenly around all cylinders. This even
sealed

directing the of cooling air to all parts of the engine distribution of air aids in preventing one or more
cylinders
Ompartment. W urawnfrom the lowerpart of the from being excessively hotter than the others. The cylinder
con
ngine comparune ne pumping action of the exhaust fins radiate heat from the cylinder walls and heads. As tne
A S e s through tne eXnaUstejectors. This type of cooling air passes over the fins, it absorbs this heat, carries it away
as
from the cylinder, and is exhausted overboard through the
Ystem eliminates tne use OI controllable cowlfiaps and
ys
sures adequate engine cooling at all operating speeds. bottom rear of the cowl.

Reciprocating Engine Cooling System The controllable cowl flaps provide a means of decreasing
Maintenance or increasing the exit area at the rear of the engine cowling.
The engine cooling system of most reciprocating engines Figure 6-54] Closingthe cowl flaps decreases the exit
uspalyconsists of the enginecowling,eylinderbaffes, arca, which effectively decreases the amount of air that can
inder fins,gnd someusea typeofcowlfaps. In additionto circulate over the cylinder fins. The decreased airfiowcannot*
the units, there are also some temperature-indicating carry away as much heat; therefore, there isatendency engine
temperaturetends to increase, Openingthe cowlflaps makes
svstems, such ascylinder headtemperature, oil temperature, the exit area larger. The flow of cooling air over the cylinders
and exhaust gas temperature.
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Exhaust stack

Ambientair
Exhaust

Fiqure 6-53. Engine cooling and exhaust system.

6-35
 Cowi ftep control leve
2 Position bracket
3 Left cowl flap controt
4Cowi fieps
5Aight cowi fiap contro

Flgure 6-54. Small aircraft cow? flaps.

increases, absorbing more heat and the engine temperature An air seal is constructed of rubber material, bolted to a
tends to decrease. Good inspection and maintenance in the metal rib riveted to the cowl panel. [Figure 6-55] This seal,
care of the engine cooling system aids in overall efficient as the name implies, seals the air in the engine section,
and economical engine operation.
preventing the air from escaping along the inner surface
of the panel without circulating around the cylinders. The_
Maintenance of Engine Cowling engine air seal must be used on engines that have a complete
Of the total ram airffow approaching the airborne engine cylinder baffling system that coversthe cylinder heads. Its
nacelle, only about 15to 30 percententers the cowling to purpose isto force the airto circulate around andthrough the
provide engine cooling. The remaining air ffows over the baffe system. Inspect the cowl panels during each regular
outside of the cowling. Therefore, the external shape of the engine and aircraft inspection. Removing the cowling for
cowl must be faired in a manner that permits the air to fiow maintenance provides an opportunity for more frequent
smoothly over the cowl with a minimum loss of energy. inspection of the cowling.

The engine cowling discussed in this section is typical of Inspect the cowling panels for scratches, dents, and tears
that used on many radial or horizontally opposed engines. in the panels. This type of damage causes weakness of the
All cooling systems function in the same manner, with minor panel structure, increases drag by disrupting airflow, and
engineering changes designed for specific installations. contributes to the starting of corrosion. The cowling panel
latches should be inspected for pulled rivets and loose or
Thecowlis manufactured in removable sections, the number damaged handles. The internal construction of the panel
varies with the aircraft make and model. The installation should be examined to see that the reinforcing ribs are not
shown in Figure 6-55 contains two sections that are locked cracked and that the air seal is not damaged. The cowl fap
together when installed. hinges, if equipped, and cowl flap hinge bondings should be
checked for security of mounting and for breaks or cracks.
The cowl panels, made from sheet aluminum
or
composite These inspections are visual checks and should be performed
material, have a smooth external surface to permit Irequently to ensure that the cowling is serviceable and
is
undisturbed airilow OVer the cowl. The internal construction contributing to efficient engine cooling.
is designed to give strength to the panel and, in addition, to
providereceptacles for the toggle latches, cowl support, and
engine air seal. X

6-36
 High pressure area

Aircraft supplied cooling batfies

Ran air

LOWpressure area

Cooling air exit

Cowl flaps
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Figure 6-55. Differential air cooling.

Engine Cylinder Cooling Fin Inspection

The cooling fins are of the utmost importance to the
cooling system, since they provide a means of transferring
thecylinder heat to the air. Their condition can mean
the difference between adequate or inadequate cylinder
cooling. The fins are inspected at each regular inspection.
Fin area is the total area (both sides of the fin) exposed to
theair. During the inspection, the finsshould be examined
for cracks and breaks. [Figure 6-56] Small cracks are not
a reason
These cracks can be filled or
for cylinder removal.
evensometimesstop-drilledto prevent any further cracking
Rough or sharp corners on fins_can be smoothed out by
filing, and this action eliminates a possible source of new
Cracks. However, before reprofiling cylinder cooling fins,
consult the manufacturer's service or overhaul manual for
the allowable limits.

The definition of fin area becomes importantin_the Flgure 6-56. Regulating the cooling airflow.
nation of fins for broken areas. It is a determining
or removal. For example,
on
21r cylinder acceptance

6-37
 speeded up agan and smoothly with the airstrean
merges
ream.
a certain
engine.if mor than 12 inches in length of any one is

or if The pressure difterential bet ween thC top and the bottor
nn. as measured al its base. is completely broken off. ttom
the total fins broken on any one eylinder head exceed 83 of the engine forces the ur past the cylinders through the
The batfles
passages formed by the detlectors. and deilecior
uare inches of area. the cylinderis removed and replaced.
size normally are inspected during the regular engine inspectio
Ihereason
wouid fora removal
cause
in this case is that an area of that
hot spot on the cylinder: since very little heat but they should be checked whenever the cowling is remo
tion,
ed
transfer could occur. for any purpose. Checks should be made for cracks, dente
orloosehold down siuds. Cracks or dents, ifsevere
enoueh
Where adjacent fins are broken in the same area. the total would necessitaterepair orremovaland replacement ofthese
units. However. a crack that has just started can be stop-
iength of breakage permissible is six inches on any two
adjacent fins. four inches on any three adjacent fins, two drilled, and dents can be straightened, permitting further
er
service from these baffles and deflectors.
inches on any four adjacent fins., and one inch on any five
adjacentins. Ifthebreakage length in adjacent fins exceeds
this prescribed amount, the cylinder should be removed and cylinder Temperature Indicating Systems
replaced. These breakage specifications are applicable only This system usually consists of an
indicator, electrical
to the engine used in this discussion as a typical example. wiring, and a therm0COuple. The wiring is between the
In each specific case. applicable manufacturer' s instructions instrument and the nacelle firewall. At the firewall, one
end
should be consulted. of the thermocouple leads connects to the electrical
wiring
and the other end of the thermocouple leads connects to
Cylinder Baffle and Deflector System Inspection the cylinder. The
thermocouple consists of two dissimilar
Reciprocating engines use sonme type of intereylinder and metals,generallýconstantan andiron,connected by wiring 4
cylinder head baffies to force the cooling air into close to an indicating System. If the temperature of the junction is
contact with all parts of the cylinders. Figure 6-50 shows a different from the temperature where the dissimilar
metals are
baffle and deflector system around a cylinder. The air baffle
connected to wires, a voltage is produced. This voltage sends
blocks the flow of air and forces it to circulate between the acurrent through wires to the indicator, a current-measuring
cylinder and the deflectors Figure 6-57 illustrates a baffle instrument graduated in degrees. *
and deflector arrangement designed to cool the cylinder
head. The air baffle prevents the air from passing away The thermocouple end that connects to the cylinder is either
from the cylinder head and forces it to go between the head
and deflector. Although the resistance offered by baffles to
the bayonet or gasket type, To install the bayonet type, the
knurled
nut is pushed down and turned clockwise until
it is
thepassage of the coolingair demands that an appreciable snug. [Figure 6-58] In removing this type, the nut is
pressure differental be maintained across the engine to obtain down and turned counterclockwise until released. Thepushed
the necessary airflow, gasket
the volume of cooling air required is_type fits under the spark
plug replaces
and the normalspark
greatly reduced by employing properly designed and located plug gasket. [Figure 6-59/(When
cyinderdefiectors installing a thermocouple
lead, remember not to cut off the lead because it is too long
but coil and tie up the excess length. The thermocouple
is designed
Cow panel air sea
to produce a given amount of resistance.)lf
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Airbaffle
Deflector
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This part of the probe presses against

thecylinder head when installed

Figure 6-57. Cylinder head bafle and deflector system. henutlocktheprodein thecylinder head socket
As shown in Figure 6-55, the airfiow
approaches the nacelle
and piles up at the top of the engine,
creating a high pressure
in the top of the cylinders. This piling up of the air reduces
the air velocity. The outlet at the bottom rear of the
cowling
produces a low-pressure area. As the air nears the cowl exit, it Figure 6-58. Bayonet type CHT prob.

6-38
 Gasket type cyinder head temperature probe

Figure 6-59. Gasket type CHT probe.

Figure
thelength of the leadisreduced an incorTect temperature
comb
reading results. The bayonet or gasket of the thermocouple stroke
is inserted or installed on the hottest cylinder of the engine,
as determined in the block test. When the thermocouple
The b-
is installed and the wiring connected to the instrument,
the indicated reading is the cylinder teimperature. Prior to nearly
of the
operating the engine, provided it is at ambient temperature,
to pr
the cylinder head temperature indicator indicates the free
woul
outside air temperature; that is one test for determining amou
that the instrument is working correctly. The cover glass of engin
the cylinder head temperature indicator should be checked engir
regularly to see that it has not slipped or cracked. The 2,100
cover glass should be checked for indications of missing ofth
or damaged decals that indicate temperature limitations. If enco
the thermocouple leads were excessive in length and had arou
to be coiled and tied down, the tie should be inspected for a litt
security or chafing of the wire. The bayonet or gasket should carri
be inspected for cleanness and security of mounting. When
operating the engine, all of the electrical connections should The
be checked if the cylinder head temperature pointer fluctuates. com
indu
Exhaust Gas Temperature Indicating Systems and
The exhaust gas temperature indicator consists of a freq
thermocouple placed in the exhaust stream just after the air i
to the effic
cylinder port. [Figure 6-60] It is then connectedfor the
instrument in the instrument panel. allows
This whi
large effect on engine larg
adjustmentofthemixture, which has a the burr
emperature. By using this instrument to set the mixture,
befc
monitored.
ugine temperature can be controlled and
Coc
Turbine Engine Cooling of t
air are burned
he intense heat generated when fuel and cas
be provided for
necessitates that some means of cooling engines are
fro
au
internal combustion engines. Reciprocatingto the cylinders
bea
over fins attached
either by passing air
oEd the
Y passing liquid
a coolant through jackets that surround on
made easier because
Cylinders. The cooling problem is