Onan T260G User manual

ONAN T260G ENGINE SERVICE MANUAL
Table of Contents – Page 1 of 2
SAFETY PRECAUTIONS
GENERAL
PROTECT AGAINST MOVING PARTS
BATTERIES
FUEL SYSTEM
EXHAUST SYSTEM
EXHAUST GAS IS DEADLY!
COOLING SYSTEM
KEEP THE UNIT AND SURROUNDING AREA CLEAN
INTRODUCTION
EXHAUST GAS IS DEADLY!
GENERAL INFORMATION
INTRODUCTION
ENGINE MODEL REFERENCE
SPECIFICATIONS
DIMENSIONS AND CLEARANCES
ASSEMBLY TORQUES
ENGINE TROUBLESHOOTING
OIL SYSTEM
CRANKCASE OIL
OIL FILTER CHANGE
CRANKCASE BREATHER
PRESSURE LUBRICATION
FUEL SYSTEM
CARBURETOR
CARBURETOR OVERHAUL
PULSATING-DIAPHRAGM FUEL PUMP
AIR CLEANER
DASHPOT ADJUSTMENT
GOVERNOR ADJUSTMENT
IGNITION AND BATTERY CHARGING
BREAKER POINT IGNITION SYSTEM
IGNITION TIMING
ELECTRONIC IGNITION SYSTEM
IGNITION TIMING
BREAKER POINT AND ELECTRONIC IGNITION COILS
SPARK PLUGS
BATTERY INSPECTION
BATTERY JUMP STARTING
FLYWHEEL ALTERNATOR
ALTERNATOR OUTPUT TEST
STARTING SYSTEM
ELECTRIC STARTER

ONAN T260G ENGINE SERVICE MANUAL
Table of Contents – Page 2 of 2
ENGINE DISASSEMBLY
DISASSEMBLY/ASSEMBLY
VALVE SYSTEM
TAPPETS
VALVE FACE AND SEAT GRINDING
FLYWHEEL
GEAR COVER
GOVERNOR CUP
TIMING GEARS
PISTONS AND CONNECTING RODS
CYLINDER BLOCK
CRANKSHAFT
BEARINGS
CRANKSHAFT ENDPLAY
CHECKING CONNECTING ROD BEARING CLEARANCE
OIL SEALS
PISTON ASSEMBLY
INSTALLATION OF PISTON IN CYLINDER
CYLINDER HEADS
CYLINDER HEAD STUD TEST AND REPLACEMENT PROCEDURE
ALIGNING BLOWER WHEEL, VENTURI AND CHAFF SCREEN

Service
Manual
Engine

Safety Precautions
It isrecommended that youread your engine manual and
become thoroughly acquainted withyour equipment before
you start the engine.
This symbol if used warns of imme-
diatehazardswhich will resultin
severe personal injuryor death.
WARNING
CAUTION
Thissymbolrefersto ahazard or
unsafe practice which can result in
severe personal injury or death.
Thissymbolrefersto ahazard or
unsafepractice which can resultin
personal injury or product or property damage.
Fuels, electrical equipment, batteries, exhaust gases and
movingpartspresentpotentialhazards that canresult in
serious, personal injury.Take care in followingthese recom-
mended procedures. All local,state and federal codes should
be consulted and complied with.
Thisengineisnotdesignedor in-
k!!!!!!!!!!! tended for usein any type ofaircraft,
Useof this engine in aircraft can result in engine failure
and causes serious personal injuryor death.
General
Provideappropriate fire extinguishers and install them in
convenient locations. Use an extinguisher rated ABC by
NFPA.
Makesure that allfasteners onthe engine aresecure and
accuratelytorqued. Keep guards inposition over fans,
driving belts, etc.
If itis necessary to make adjustments while the engine is
running,useextremecaution whencloseto hotexhausts,
moving parts, etc.
Protect Against Moving Parts
Do notwear loose clothing inthe vicinityof moving parts,
such as PTO shafts, flywheels, blowers, couplings,fans,
belts, etc.
Keep your handsaway from moving parts.
Batteries
Before starting work on the engine, disconnect batteries
to prevent inadvertent startingof the engine.
DO NOT SMOKE whileservicing batteries.Lead acid
batteries give
off a highly explosive hydrogengas which
can be ignited byflame, electrical arcing or by smoking.
Verify batterypolaritybefore connecting battery cables.
Connect negative cable last.
Fuel System
DO NOT fill fuel tanks while engine is running.
DO NOTsmoke or usean open flame inthe vicinityof the
engineor fueltank. Internal combustion enginefuels are
highly flammable.
Fuellines must be of steel piping, adequatelysecured,
and free from leaks. Pipingat the engineshouldbe
approvedflexible line.Donotusecopper piping for
flexiblelines as copper willwork harden andbecome
brittle enough
to break.
Be sure all fuel supplies have a positive shutoff valve.
Exhaust System
Exhaust products of any internal combustion engine are
toxic and can cause injury,or death
if inhaled. All engine
applications,especiallythosewithina confined area,
should beequipped withanexhaust systemto discharge
gases to the outsideatmosphere.
Do not use exhaust gases to heat a compartment.
Make sure that your exhaust system is free of leaks.
Ensure that exhaustmanifoldsaresecure and arenot
warped by bolts unevenly torqued.
Exhaust Gas is Deadly!
Exhaust gases contain carbon monoxide,apoisonous gas
thatcancauseunconsciousnessand death. It is an odorless
and colorlessgas formed during combustionof hydrocarbon
fuels. Symptoms of carbon monoxide poisoning are:
Dizziness Vomiting
Headache Muscular Twitching
Weakness and Sleepiness Throbbing in Temples
If you experienceanyof thesesymptoms, getout intofresh air
immediately, shut down the unit and do not use until
it has
been inspected.
Thebest protection against carbon monoxideinhalationis
proper installation and regular,frequent inspections
of the
complete exhaustsystem.If you notice a changeinthe sound
orappearance
of exhaustsystem,shuttheunitdown
immediately and haveit inspected and repaired atonce by a
competent mechanic.
Cooling System
Coolants under pressurehave a higherboiling point than
water. DO NOT openaradiatorpressure cap when
coolant temperature is above
212F (100°C) or while
engine is running.
Keep the Unit and SurroundingArea Clean
Makesure thatoily rags are notleftonor near the engine.
Remove all unnecessary grease andoil from the unit.
Accumulatedgreaseand oilcan causeoverheating and
subsequent engine damage and present a potential fire
hazard.
E-6

Table' ofContents
TITLE PAGE
General Information . l-1
Speclflcations.. .2-1
Dimensions and Clearances .3-1
Assembly Torques and SpecialTools .4-1
EngineTroubleshooting .5-1
OilSystem .6-1
Fuel System .7-1
Ignition and Battery Charging.. .8-1
Starting System .9-1
EngineDisassembly .10-1
WARNING]
EXHAUST GAS IS DEADLY!
Exhaust gasesfromallfuels (includingdiesel, gasoline, liquidpropane, natural
gas)contain carbonmonoxide, anodorlessandcolorlessgas. Carbonmonoxide
ispoisonousand can cause unconsciousness anddeath. Symptoms ofcarbon
monoxidepoisoningcaninclude:
Dizziness Throbbingin Temples
Nausea Muscular Twitching
Headache Vomiting
Weakness and Sleepiness Inability to ThinkCoherently
IF YOU OR ANYONE ELSE EXPERIENCE ANY OF THESE SYMPTOMS, GET OUT
INTOTHEFRESHAIRIMMEDIATELY. .If symptoms persist, seek medical
attention. Shutdown the unitanddo not operateuntil ithas beeninspectedand
repaired.
Protection against carbon monoxide inhalation includes proper installation,
ventilation andregular, frequentvisualand audible inspections
of the complete
exhaust system.
iii

General Information
INTRODUCTION
Thismanualdealswith specific mechanicalandelec-
trical information needed byengine mechanics for
troubleshooting, servicing, repairing,or overhauling
the engine.
Usethe tableof contents for a quickreferencetothe
separateengine system sections.
Use the separate Parts Catalogs available at the
dealer level,for parts identification and forestablish-
ing their proper location onassemblies.
Thetroubleshootingguideisprovided as aquick
referencefor locating and correcting engine trouble.
The illustrations and procedures presented in each
section applytothe engines listedon thecover. The
flywheel-blower endof the engine is the front end
so
right and left sides are determined by viewingthe
engine from the front.
The disassembly sectioncontainsmajoroverhaul
procedures for step by step removal, disassembly,
inspection,repairandassembly of theengine
components.
If amajor repairoranoverhaul isnecessary,a compe-
tent mechanic should eitherdothe job orsupervise
and check thework of the mechanicassigned to do
the jobtoensurethat alldimensions, clearances and
torque values are within the specifiedtolerances.
The wiring diagram on the last page of the manual
shows howtheelectricalcomponents are inter-
connected.
A partscatalog (availableat thedealerlevel)contains
detailedexploded views of each assembly and the
individual piecepartnumbers and their propernames
for orderingreplacement parts.
Useonly Genuine Onanreplacement parts toensure
qualityandthe best possible repair and overhaul
results. When ordering parts, always use thecom-
plete Model and Spec number as well as the Serial
number shown on thenameplate.
ENGINE MODELREFERENCE
Identify your model by referring to theMODEL and
SPEC (specification)NO. as shown on the unit
name
plate Always use this number and the engine
serial numberwhen making referenceto yourengine.
How to interpret MODEL and SPEC
NO
2 60G G A 024 1 A
1234567 89
1. Factorycodefor general identification of basic
2. Number of cylinders.
3. Cubic inch displacement.
4. Engine duty cycle.
5. Fuel required(G=gasoline).
6. Cooling system description
(A=air-cooling-pressure).
7. BHP rating.
8. Factory code fordesignated optional equipment,
9. Specification (spec letter) which advances with
engine series.
if any.
factory production modifications.
WARNING I
INCORRECTSERVICE OR REPLACEMENTOF PARTSCANRESULTINSEVERE
PERSONAL INJURY AND/OR EQUIPMENT DAMAGE. SERVICE PERSONNEL
MUST BE QUALIFIED TO PERFORM ELECTRICAL AND/OR MECHANICAL
SERVICE.
1-1

Specifications
This manual contains SI metric equivalents that follow immediately in parentheses
after the
U.S. customary units of measure.
UNIT OF
SERIES
SPECIFICATION MEASURE
T-260G
Number of Cylinders
2
Bore in 3.56
(mm) (90.48)
Stroke in 3.0
(mm) (76)
Displacement cu in 60
(cm3) (983)
CompressionRatio 7.0 to 1
RatedSpeed (Maximum) RPM
3600
Powerat BHP
24
RatedSpeed (kw)
(17.9)
Oil Filter
Full Flow
OilCapacity Without Qt
2.5
Filter(litre) (2.4)
OilCapacityWith Qt 3.0
Filter Change(litre) (2.8)
Crankshaft Rotation
(viewedfrom flywheel)Clockwise GovernorVariable Speed Mechanical
Valve Clearance (Cold)
Intake in
.005
(mm) (0.13)
Exhaust in .013
Spark PlugGap in .025
(0.64)
Breaker PointGapStatic(SpecA-E) in .020
(Full Separationand EngineCold) (mm) (0.51)
IgnitionTiming BTC
20°
CylinderCompression psi
75 to 115
(mm) (0.33)
(mm)
(kPa)__
517 to 793
2-1

Dimensions and Clearances
All clearances given at room temperature of 70°F (21 C) All dimensions in inches (approximate miilimetre dimensions in
parentheses) unless otherwise specified
DESCRIPTION MINIMUM MAXIMUM
CYLINDER
BLOCK
MaximumAllowable
Inches (mm) Inches (mm)
Cylinder Bore Honed Diameter 3.5625(90.49)3.5635(90.51)
Out-of-Round 0.003(0.08)
Main Bearing InsideDiameter (Installed) 2.0015(50.84)2.0040(50.90)
Camshaft BearingBore(BearingInstalled) 1.3760(34.95)1.3770(34.98)
Taper0.003(0.08)
Main Bearing InsideDiameter(Without bearing) 2.187
(55.55) (2.188(55.58)
InterferenceStud Heightfrom Top Surface ofBlock
Spec C, D, E
Top2 2.00(50.80)(2.06(52.32)
Middle 41.84(46.74)1.90(48.26)
Bottom41.16(29.46)1.22(30.99)
Main BearingJournal Diameter1.9992(50.78)
2.0000 (50.80)
SpecA-E 0.0025(0.064) 0.0038(0.097)
BeginSpec F 0.0024(0.061) 0.0042(0.107)
ConnectingRodJournal Diameter 1.6252(41.28) 1.6260(41.30)
Crankshaft End Play
0.005 (0.13) 0.009(0.23)
and rod bolts properlytorqued 1.7505(44.46) 1.7510(44.48)
Connecting Rod SideClearance 0.0020(0.051) 0.0160(0.406)
Piston Pin BushingBore(Withoutbearing) 0.8115(20.61) 0.8125(20.64)
(Finishedbore) 0.7504(19.06)0.7508(19.07)
AluminumRod 0.0020(0.051)0.0033(0.084)
Iron Rod 0.0020(0.051)0.0033(0.084)
BearingJournal Diameter 1.3740(34.90)1.3745(34.91)
Bearing Clearance
0.0015 (0.038)0.0030(0.076)
Spec A-E 0.0030(0.076)0.0120(0.305)
BeginSpec F 0.011(0.28)0.048(1.22)
Begin Spec
A
0.286(7.26)0.294(7.47)
BeginSpec E 0.285(7.24)0.293(7.44)
Begin Spec
A
0.291(7.39)0.299(7.59)
CRANKSHAFT
Main BearingClearance
CONNECTING ROD
Large BoreDiameter(Withoutbearing installed
Piston Pin BushingBorewith Bearing,
Bearing
to CrankshaftClearance
CAMSHAFT
End Play
Camshaft Lift
Intake
BeginSpecF 0.305(7.75)
Exhaust
Begin SpecE
Begin SpecF 0.295 (7.49)
0.283(7.19)0.291(7.39)

DESCRIPTION
PISTON
ClearanceinCylinder
Measure
1.187 Below Topof Piston and 90" from pin . . . .. ... . ..
Piston PinBore.. . . . . .. . .. . .. . . . .... .. . .. ..... . . . .. ..... , ........ .
Ring Groove Width
Top
1 Compression Ring . ...... .. .. . .. . . .. . .... . ........ . .. ... . .
No. 2 CompressionRing.. .. .. . . .... . . ..... . ... .. . . . . . . .. . ... .. , .
No. 3 Oil ControlRing ..... . .... . . . .. . . .. .. , . ... ....... . . . . .... . .
PISTONPIN
Clearancein Piston . . . ... . ... . ...... . .. . ..... . . .... . . . ...... . ....
ClearanceinConnecting Rod
AluminumRod
Iron Rod
. . . .. .. ....... . . . ... .. .. . .. .. . . . ... . .. ....... .. ... .... .
Diameter. . . . . . .. .... . .. . . . . .. . ... . .. ..... . . .. .. . ... . ... . . . . . . .. . .
-PISTON RINGS
Clearance
Top Groove
Ring End GapinCylinder
... .. . . .. ... . ... . . . . .. . . ... .. . . ... . . . .. .
INTAKE VALVE
Stem Diameter . . . .. . . . .. .. . .. . . . . . . . . .... .. . . .. .. . .. ..... .. . . . ..
Clearance (Stemto Guide) . . .. ... . . . .. .. . . . .. . . .. . . . .. . . . . ... . .. .
Valve FaceAngle . . ..... . ... . . . . . . ... ..... ..... . .. . . . . . . .... . . . ..
tNTAKE VALVE SEAT
Seat Cylinder Head Bore Diameter.. ... . . . . . .. . . . . . . .. . . . . .. .. .. . .
Seat Outside Diameter . ....... . .... . .. . .... .... .... . .. . .. . . .. . . . .
Valve SeatWidth ..... . . . . .. .. . . .. ... .. .... .. . . . . .. .... . . .. . .. . . .
Valve SeatAngle . . . . . . .. ..... . . . .. . . . .. . . .. . . .. . . .. . .. . . .. . . . .. .
EXHAUST VALVE
Stem Diameter . . . .. . . . .. . . .. . .. . . . .. . . . ....... . .. . . .. .... . . . . . . .
Clearance (Stemto Guide) .. . . ... .. . . .... .. . . . ... . . . . ... . . .. . . ...
Valve Face Angle
EXHAUST VALVE SEAT
Seat Cylinder Head Bore Diameter.. . . .. . . . . ... . . . .. . . .. . . .. . .. . ..
Seat Outside Diameter . . .... .... . .... . . .. . . . .. .. . . .. . .. . . . . . . . . . .
Valve SeatWidth . . .. . . . ... . .. . . .... . . .. . . . . . ... . . . . . .. .. . ...... .
Valve SeatAngle . ‘ . ... . . ... .. .. . . . .. . . .. . . ..... . . .... .. . . .. . . . . .
VALVE GUIDE
Inside Diameter
TAPPET
Body Diameter ... . . . . . .. ...... . .. . . .. . . . .. .. . . .. . .. . .... ..... . ..
Bore Diameter.. . . . .. . . .. . .. .. . . . .. . . .. . ....... .. . . .. . .... . .... . .
Clearancein Bore
VALVE SPRINGS INTAKEAND EXHAUST
Valve Spring Free Length (Approx.) . . .. . ..... ... ..... .. . . . ... . ....
Valve Spring Length
Valve Open..
. .. . .... . .. . . .. ........... . . . . . . . . . . . . . . . .... ... . .
ValveClosed
Spring Load
@ 1.375 inch (Valve Closed). ....... . .. . ....... . .... . .
Spring Load @ 1.125 inch (Valve Open) . .. . ........ . ...... . ..... ..
MINIMUM
MAXIMUM
Inches (mm)
Inches (mm)
0.0070 (0.1 78)
0.0090 (0.229)
0.7502 (19.055) 0.7506 (19.065)
0.080 (2.032) 0.081 (2.057)
0.080 (2.032) 0.081 (2.057)
0.188 (4.775) 0.189 (4.801)
0.0001(0.003)
0.0005 (0.013)
0.0002
(0.005)
0.0008
(0.020)
0.0002
(0.005)
0.0008
(0.020)
0.7500
(1 9.05) 0.7502 (19.06)
0.002
0.010
0.3425
0.0010
1.5645
1.5690
0.031
0.3410
0.0025
1.2510
1.2550
0.031
0.344
0.7475
0.7500
0.0015
38
Ib.
71 Ib
(0.051) 0.008
(0.254)
0.020
(8.70)0.3430
(0.025)0.0025
440
(39.74) 1.5655
(39.85) 1.5700
(0.787) 0.047
45O
(8.661)0.3420
(0.064)
0.040
440
(31.78) 1.2520
(31.88) .1.2560
(0.787) 0.047
45O
(8.74)0.346
(1 8.99) 0.7480
(1 9.05) 0.7515
(0.038) 0.003
1.662 (42.21)
1.125 (28.58)
1.375 (34.93)
(17
kg)
42 Ib.
(32 kg)
79 Ib
(0.203)
(0.508)
(8.71)
(0.064)
(39.76)
(39.88)
(1.194)
(8.687)
(0.1 01)
(31.80)
(31.90)
(1.194)
(8.79)
(1 9.00)
(1 9.09)
(0.076)
3-2

DESCRIPTION MINIMUM MAXIMUM
Inches (mm)
Inches (mm)
GEAR BACKLASH
Timing Gear
Spec
A-E
BeginSpec F
spec A-E
BeginSpec F
Oil Pump Gear
GOVERNOR
Dashpot to Governor Arm Bracket..
0.002 (0.051) 0.003
(0.076)
0.001 (0.025) 0.005
(0.127)
0.002 (0.051) 0.005 (0.127)
0.001 '(0.025) 0.008 (0.203)
0.040 (1.02) 0.060 (1.52)
3-3

Assembly Torques
The torque values given in Table 1 have been deter- Check all studs,nuts, and capscrews, and tighten as
mined for the specific applications. Standard torque requiredto keepthemfrom working loose.Referto the
valuesmust not be used wherethose listed in Table
1 PARTS MANUAL forthelocation of washers and
apply. The engine assembly torques given here will capscrews.
assure proper tightness without danger
of stripping
threads.
All threads must beclean and lubricated with
new engineoil beforetorquing.
DESCRIPTION
Cylinder Head Nuts(with
Compression Washers)
SpecA-E
Begin Spec F
Cylinder Head Nuts(without
Compression Washers)
SpecA-E
Rear BearingPlate
Connecting Rod Bolt
SpecA-E
BeginSpec F
FlywheelCapscrew.
Starting Mounting Bracket
to Oil BaseScrews.
Begin Spec F
TABLE 1.
TORQUE
SPECIFICATIONDESCRIPTION F1.-Lb.Nm
Gear CaseCover.
Oil Pump.
14 Valve Cover.
ExhaustManifold Mounting
11-13(15-18) IntakeManifold Mounting
(19) Screws
14-16(19-22) Screws
17
25-28(34-38)BeginSpec F
Other 1/4”/4" Cylinder Block Studs
(23)Spec
A-E
14-16 (19-22) and Nuts
27-29(37-39) Other 5/16" Cylinder Block
50-55(67-75) Studsand Nuts
24-26(33-35) Nuts.
Other 3/8” Cylinder Block
TORQUE
SPECIFICATION
F1.-Lb.Nm
8-10(11-14)
7-9 (10-12)
(27-31)
4-8
( 5-11)
20-23 (27-31)
9-11 (12-15)
7-9 (10-72)
8-10(11-13)
18-23(24-31)
Special Tools
Thefollowingspecialtoolsareavailablefrom
Onan. Forfurther informationsee
TOOL CATALOG
900-0019.
Valve Seat Driver
Valve Guide Driver
Oil Guide and Driver
Combination Bearing Remover (Main andCam)
Combination Bearing Driver (Main andCam)
Flywheel Puller
4-1

Engine Troubleshooting
I IGNITIONSYSTEM
FUEL SYSTEM
INTERNAL ENGINE
COOLING SYSTEM (AIR COOLED)
THROTTLE AND GOVERNOR
M-1686-1
5-1

Oil System
CRANKCASEOIL
Refer to engine nameplate or Periodic Maintenance
Schedule, located
in theOperator'sManual,for oil
change interval. If operating in extremelydusty, high
ambient, or low ambient conditions change oil more
often.
Run engine until thoroughly warm before draining oil.
Stopthe engine,placea panunderthe drain outletand
removethe oil drain plug or open the drain valve. After
the oil is completely drained, replace the drain plug or
close the drain valve. Refill with oil of the correct API
classification and appropriate SAE viscosity grade for
the temperatureconditions.
Oilmust meetorexceedtheAPIdesignationSF, SF/CC
or SF/CD. Refer to the chart to determine the proper
viscosity grade of oil to use. Straight weight oils are
recommendedfor severeduty useandattemperatures
above
32" F(0°C) for minimumoil consumption.
Crankcase pressure can blow out hot
oilandcauseseriousburns.
Do NOT
WARNING
check oil while the engine is operating.
Hot crankcase oilcan cause burnsif
itis spilled or splashed on skin. Keep
fingers and hands clear when removing the oil drain
plug and wear protective clothing.
ALWAYS REPLACE
LEAKAGE MAY
OCCUR
TIGHTLY OR OIL
FIGURE 1. CRANKCASE OIL FILL
CAUTION
Do not overfill crankcase. Excessoil
causes higheroperatingtempera-
tures and
may cause foaming.
Oil levelshouldbetothe FULL mark ofthedipstick.Start
engine and run for a short time to check for oil leaks
around the drain plug.
LS-1170
I COOLING FINS
FILTER
FILTER 2. OIL FILTER
OIL FILTER CHANGE
Refer to engine nameplate or Periodic Maintenance
Schedule,locatedinthe Operator's Manual,for oilfilter
change interval. If operating in extremelydusty, high
ambient, or low ambient conditions change oil more
often.
Spin
off oil filter element and discard it. Thoroughly
cleanfilter mountingsurfaceand makesurenew gasket
is insertedin the element.
6-1

Applya thinfilmof oiltothegasket.Spinelementdown
by hand until gasket just touches mounting pad and
then turn down an additional
1/2-3/4 turn. Do not
overtighten.
With oil incrankcase, startengine and check for leaks
aroundfilter element. Retighten only as much as
necessaryto eliminate leaks;do notovertighten.
CRANKCASE BREATHER
The crankcase breather prevents pressure from
buildingupin the crankcase. It also prevents oil
contaminationby removing moistureor gasoline
vaporsand other harmful blow-bymaterialsfrom the
crankcase.Thesevaporsareroutedto thecarburetor
wherethey aremixedwith incoming air and burned in
the combustionchamber.
A stickybreathervalvecan
cause leaks, highoilconsumption,rough idle,
reduced engine power andarapidformation of
sludge and varnish within theengine.
Crankcase BreatherService
Thisengine uses.a crankcase breather valve for
maintaining crankcase vacuum. Ifthe crankcase
becomespressurizedas evidenced by oilleaksat the
seals, clean baffleand valve inasuitable solvent.
BREATHER
HOSE
CAPAND VALVE
HOSE CLAMP
FIGURE 3. CRANKCASEBREATHER
Clean orreplacecrankcasebreatherbaffleperiodically.
Besurebafflematerial-doesn’tcomeapartandworkinto
themanifold.
To disassemble, remove breather hose from cap and
valve assembly. Remove cap and valve assembly and
washin asuitablesolvent. Replacecapandvalveifballs
do not move freely.Pull baffleout and washin solvent.
To allow free operation of the valve, screens must be
positionedas shown in Figure
3.
PRESSURE LUBRICATION
All engines usean oilpumpto provideaconstantflow
of oiltotheengine parts.Theoilsupplycollectsinthe
oil basewhere itis picked up by the oil pump pick-up
cup.
A by-pass valve is usedtocontroloil pressure.
Drainoil beforeremoving oil base and always usea
new gasket when replacing theoil base.
Oil Pump
The oil pump (Figure 4) is mounted behind the gear
coverand isdrivenbythecrankshaftgear. Inletpipeand
screen assembly are attached directly to the pump
body.Adischargepassageinpumpcoverregisterswith
a drilled passage in the crankcase. Parallel passages
distribute oil to the front main bearing, rear main
bearing,and pressurecontrol bypass valve.
OIL PUMPPICK-UP CUP
OIL PUMPASSEMBLY
CRANKCASETURNED
ONLEFT SIDE
FIGURE 4. OIL PUMP ASSEMBLY
6-2
LS-1109

Circumferential grooves in the main bearings supply
oil to connecting rod bearings through drilled pas-
-.,sages from eachmainjournal.
A drilled passage
\connects thefront mainbearingoilsupplyto
the front
'camshaft bearing; rear cam bearing
is splash lubrica-
ted. Oil overflowfromthebypass valve provides
lubrication to thecamshaft drivegears.
Normal oil pressureshouldbe
30 psi (207 kPa) or
higherwhen the engineisat normal operatingtemper-
ature.
If pressure drops below thisvalue at governed
speed, inspectoil system for faulty components.
Checkoil pump thoroughly for wornparts. Oil pump
toprime it before reinstalling.Exceptforgaskets and
pick-up cup, component partsof the pump are not
available individually. Install anewpumpassembly
if
any parts are worn.
Oil By-Pass Valve
The by-passvalve (locatedto therightand. behindgear
cover, Figure
5) controlsoilpressurebyallowing
excess oil to flow directly backtothe crankcase.
Normallythevalvebeginstoopenabout
20 psi
(138 kPa).
The valve is non-adjustable and normally does not
needmaintenance.Determine
if valve isoperating
normally by inspecting plunger actionas follows:
1. Remove the 3/8 x 24 x 7/8 capscrewlocated
behind gear cover and under governorarm.
2. Removespring and plunger with amagnet tool.
3. Determineproper valve operationbychecking
the spring and plunger according to the following
measurements.
Plunger Diameter..
0.3105 to 0.3125 in.
(7.89 to 7.94 mm)
Spring
Free Length..
1.00 inch (25.4 mm)
Load
2.6Ifr0.2 Ibs. (11.6+0.9N)
whencompressed to 0.5 inch (12.7 mm)
4. Checkthevalve seatand cleanaway anyaccumu-
lation of metal particles which could causeerratic
valve action. Verify that the valve seatisnot damaged.
5. Cleanplungerand springinparts cleaningsolvent
and install.
FIGURE 5. BY-PASSVALVE
6-3

Fuel System
CARBURETOR Set the adjustmentscrew about 1/8 turn outward
(rich) from the midpoint
of this range. On Nikki
The carburetor mixture screw settings weresetfor carburetors the idle adjustment is limited
to 1/8
maximumefficiency at thefactory andshould normally turn.Do not go beyondtheselimits.
notbedisturbed.
If adjustmentsseemnecessary,firstbe
suretheignition system isworkingproperlyand
governor sensitivity isproperlyadjusted.
If adjustment is needed, refer to Figures 1 and 2 and
proceedas follows:
THROTTLE
CAUTION
Forcingthemixtureadjustment
screw tight will damage the needle
and seat.
Turn in only until light tensioncan be felt.
1. Walbro mixture screw settings:
Turn both mixture screws in until lightly seated
(Figure
l), thenbackthe idlemixturescrewout 1/2
turn andthemain mixturescrew out 1-3/4turns. AND LIMITED IDLE MIXTURE SCREW.
FS-1406-2
NlKKl CARBURETOR WITH SEMI-AUTOMATIC CHOKE
Nikki limited idleadjustmentmixturescrew
settings:
The carburetor hasa limited idle adjustment range
between stops
1/8 turn.Thescrewshouldonly
be adjusted within these limits; in
to lean the
mixture, out to richen. There is no main mixture
adjustment.
MAINFUEL
When replacingtheidlemixturescrew,turn inuntil
lightly seated,then back screw out
1-1/2 turns.
Replace limiter cap
so thetab is approximately ADJUSTMENT
centered.
ADJUSTMENT
IDLEFUEL
FS-1002
2. Starttheengineand allow it to warm upthoroughly
(at least
10 minutes).
Someequipmentmanufacturersmayrequirehigher
throttle stop speed and governor low speed rpm
settings. Refer
to equipmentmanufacturer’sOpera-
tor’s Manualfor thecorrect rpmsettings.Whenrpm
settings are not specified by theequipment manu-
facturer use therpmsettingslistedinSteps 3 and
5.
3. Movetheenginespeedcontroltotheslowposition.
Back out the low speed screw on the governor
so
the throttle stop screw on the carburetor controls
engine speed (Figure
2). Adjustthe throttle stop
screw for
1000 rpm idle.
4. Determine the best idle mixture setting by first
turning the idle adjustment screw inuntil engine
speed drops and then outward until engine speed
drops again. Over a narrow range between these
two settings, engine speed remainsat its highest.
WALBRO CARBURETOR
FIGURE 1. CARBURETORADJUSTMENT
5. Readjustthe throttle screw for 1000 rpm idle,then
adjust the governor low speed screw for
1100 rpm
idle.
6. Movethe engine speed controlto thefast position.
Bend the high speed stop on the governor
so the
engine runs at the vehicle manufacturer’s recom-
mended speed(Figure
2.)
7. Check the main mixture adjustment (Walbro car-
buretors only) by rapidly accelerating the engine
fromidle
to fullspeed. Theengineshouldaccelerate
evenlyand without hesitation.
If itdoesnot,turn the
mainadjustmentscrew out in
1/8 turn increments
until the engine accelerates smoothly, but do not
turn it out morethan
1/2 turn beyond the original
setting.
7-1

THROTTLE STOP
SCREW
HIGH SPEED
I
GOVERNOR ARM
FS-1119
FRONT PULL GOVERNOR
THROTTLE STOP
SCREW
THROTTLE PLATE
GOVERNOR CONTROL\
GOVERNOR SPRING GOVERNOR
STOP
ADJUSTMENT
SIDE PULL GOVERNOR
FIGURE 2. GOVERNORSPEEDADJUSTMENT
CARBURETOROVERHAUL
Carburetionproblemsthat are notcorrectedby
mixture adjustmentsare usually aresult of gummed-
up fuel passages or worn internal parts. The most
effective solution is a carburetoroverhaul.
In general, overhauling a carburetor consists of dis-
assembly,
a thorough cleaning, and replacement of
worn parts. Carburetorrepairpartsare available.
General instructions for overhauling a carburetorare
given below. Carefully note the position of all parts
whileremoving to assure correct placement when
reassembling Readthrough all the instructionsbefore
beginningforabetterunderstanding of thepro-
cedures involved.Carburetor componentsareshown
in Figure
3.
WARNING
Ignition of fuelcan cause serious
personal injury or death by fire or
explosion.
Do notpermit any flame, cigarette,or other
igniter near the fuel system.
FLOAT ASSEMBLY
IDLE
ADJUSTMENT
FS-1440-3
NIKKI CARBURETOR
CHOKE PLATE
WALBRO CARBURETOR
FIGURE 3. CARBURETORASSEMBLY

Removal CleaningandRepair
1. Remove air cleanerand hose.
2. Disconnect governor and throttle linkage, choke
control and fuelline from carburetor.
3. Removethefour intakemanifold cap screws andlift
complete manifold assembly from engine.
4. Remove carburetor from intake manifold.
Disassembly (Walbro)
1. Remove throttle and chokeplate retaining screws,
then plates. Pulloutthrottleand chokeshafts.
2. Remove main jetand idleadjustment needle.
3. Removeattaching screws andseparate upper and
lower carburetorsections.
4. Carefully notepositionof floatassemblyparts,then
pullout retainingpin andfloat assembly.
5. Remove needleand unscrew needle valve seat.
Disassembly (Nikki limited idle adjustment)
1. Remove main jetand idle adjustment needle.
2. Remove attaching screws andseparate upper and
3. Carefully notepositionof floatassembly parts,then
4. Remove needle valve.
lower carburetorsections.
pullout retainingpin andfloat assembly.
BEND FLOAT
0.02 0.02 INCH
TANG HERE
(0.51 0.51 mm)
TO ADJUST
FLOAT LEVEL ADJUSTMENT
.0512" .028"
FLOAT LEVEL ADJUSTMENT
1. Soak all metal componentsnotreplaced in car-
buretor cleaner.
Do not soak non-metal floats or
other non-metalparts. Follow the cleaningmanu-
facturer’s recommendations.
2. Cleanallcarbonfrom the carburetor bore, especially
where thethrottleand chokeplates seat. Becareful
notto plugthe idle or main fuel ports.
3. Dryout allpassageswith low pressureair (35 PSI).
Avoid using wireor otherobjectsfor cleaning which
may increasethe size of critical passages.
4. Check thecondition oftheadjustmentneedle;
replace
if damaged.Replacefloat if loaded withfuel
or damaged.
5. Check the choke andthrottle shafts for excessive
play in their bore. This condition may necessitate
replacement
of the carburetor.
6. Replaceold components with new parts.
I
FUEL LEVEL
0.25 INCH
(6.35 mm)
BEND FLOAT ARM
HERE TO ADJUST
FLOAT DROP
MINIMUM
0.20 INCH
(5.08 mm)
WITH FUEL
WALBRO
CARBURETOR
FUELLEVEL
.472
(12.0 mm)
WITH FUEL
NlKKl CARBURETOR
NO FUEL
FS-1524
FLOAT DROP BEND FLOAT ARM
2913" HERE TO ADJUST
MINIMUM
NO FUEL
FS-1683
FIGURE 4. CARBURETORFLOATLEVELADJUSTMENTS
7-3

Reassembly and Installation(Walbro)
1. Install needlevalveand seat, main jet and fioat
assembly. Makesurethat float pivot pin isproperly
placedand that float moves freelywithout binding.
2. Gentlypushfloat tangdown untilneedle just seats.
(Figure
4). Measurefloat level; adjust if necessary.
Releasefloattangand measurefloat drop;adjust if
necessary.When checking float level anddrop,
measure
to float body,not seam.
3. Positiongasket oncarburetorandattachcarburetor
sectionstogether with screws.
4. Slide in throttle shaftand install plate using new
screws.Beforetighteningthe screws, theplatemust
be centered in the bore. To do
so, back off the
throttle stop screw as necessary and completely
close the throttle lever. Seat the plate by tapping
withasmallscrewdriver,thentightenscrews.Install
the choke shaft andplateinthe same manner.
5. Install idle adjustment screw, throttle stop screw,
and mainfuel adjustment needle.
6. Mount carburetor on intake manifold and install
assembly on engine.
7. Mount air cleaner assembly. Connect air intake
hose,breatherhose, fuel line,vacuumline, and
throttle linkage.
8. Adjustcarburetorandgovernoraccording to direc-
tions given inthis section.
Reassembly and Installation
(Nikki limitedidle adjustment)
1. Install needle valve,mainjet, and float assembly.
Makesurefloatpivotpinisproperlyplacedandfloa/
moves freelywithout binding.
2. Turn carburetor on its side and measurefloat level
(Figure
4). Adjust float level only if necessary.
Measure float drop (the distance fromthe top of
carburetor body
to top offloat). Adjust only if
necessary.
3. Position gasket on lower carburetor section and
install upper carburetor section.
4. Install idle adjustment screw, throttle stop screw,
and fixed mainjet plug.
?
5. Mount'carburetor on intake manifold and install ?
assembly on engine.
6. Mount'air cleaner assembly. Connect air intake
hose,breatherhose, fuel line, vacuum line, and
throttle linkage.
7. Adjustcarburetorandgovernoraccording to direc-
tions given inthis section.
ASSEMBLY
SCREWS
VALVE DIAPHRAGM
REED VALVE
FIGURE 5. EXPLODED VIEW OF FACET FUEL PUMP
PULSATING-DIAPHRAGM FUELPUMP
Pulsating-diaphragmfuel pumps, orpulse pumps,rely
onchangesincrankcasevacuumto createa pulsating
movement of thepumpdiaphragm. As the engine's
pistons move outward, a vacuum is created. This
vacuumistransmitted
to the pumpdiaphragm,causing
it
to pull back and suck fuel into the pump. As the
engine's pistons move inward, crankcase vacuum is
reduced and the diaphragm return spring pushes the
pump diaphragm forward, forcing fuel through the
pump outlet.
PUMP BASE
\
Fuel Pump Test Procedure
Beforetestingmakecertainthatfuel pumpvacuumline
connections are tight and free of leaks.
1. Operateengineat anidlefor five minutes to ensure
2. Shutengine off and remove fuelinlet linefrom fuel
that carburetor isfull of fuel.
pump.
WARNING
WARNING Spilledfuelcanigniteandcause
seriouspersonalinjuryor death.
Thoroughly clean-up any spilled fuel.

3. Connect a vacuum gauge tofuelpumpinlet using a
4. Start engineandallow to idle.foratleast five
seconds. Record vacuum gauge reading.
pieceof fuel hosewith clamps.
5. Move throttle control to high idle position.Wait at
leastfivesecondsandrecordvacuumgauge
reading.
6. Shut engine off and removevacuumgaugehose
from fuel pumpinlet.Connectfuel inlet lineto fuel
pump.
i 7. Removefuel outlet linefromfuelpump.
Spilledfuelcanigniteandcause
!
WARNING seriouspersonalinjury ordeath.
Thoroughly clean-up any spilled fuel.
8. Connect a pressure gaugetofuel pumpoutletusing
a pieceof fuel hosewith clamps.
9. Start engineandallow to idle foratleastfive
seconds. While holdingpressure gauge level with
pumpoutlet, record pressuregauge reading.
10. Movethrottle control to highidlepositionand allow
enginetorunfor at least five seconds.While holding
pressure gauge level with pump outlet, record
pressuregauge reading.
11. Shut engine off and remove pressure gauge hose
fromfuel pumpoutlet.Connectfueloutletline
to fuel
pump.
Repair or replace thefuel pump
if test readings are not
within thevalues specified inTABLE
1.
TABLE 1
PULSE PUMP TEST SPECIFICATIONS
Pump *outlet
Pressure
(Minimum)
Low Idle
of mercury 1.7 psi
2.6 inches
High Idle of mercury 1.7
psi
2.6 inches
Fuel Pump Repair
This section applies onlyto Facetfuel pump. TheNikki
fuel pumpis notrepairable; replaceunit
if test readings
are notwithin the valuesspecified inTABLE
1.
1. Remove thevacuumandfuel lines. Inspect the
lines forwear,cracking or brittleness. Replaceas
necessary.
2. To' insure correct alignmentwhen reassembling,
scribe a line across the outer pump parts on each
end of the pump.
3. Holdingthe pump carefully, remove the assembly
screws(Figure
5).
4. Carefully pullapart thepump sections and check
forwornordamaged parts. Replacewith new
parts wherenecessary or install pumprepair
kit.
5. Check and unclog if necessary the small diaph-
ragm air bleedholelocatedbehindthepump
diaphragm in the pumpbase.
CAUTION hole
A clogged diaphragm air bleed
olecancausediaphragmwear
andseal damagewhileinhibitingpump operation.
6. Replacegaskets and reassemble pump.Reinstall
assembly screws, checking the scribe marksfor
proper alignment.Reinstallfuel and vacuumlines
and clamps.
WARNING and reinstalling the pump. Im-
Usecare when reassembling
proper parts alignmentor misconnectedfuellines
can result in leaking fuel, creating a serious fire
hazard.
AIR CLEANER
If aircleaner becomestoodirty,
to run' properly.Symptoms:
Loss of power, flooding,
hard starting and overheating.
engine will not receive sufficient air
Engineisequipped with apaperelement. If the
engine is equipped with polyurethaneprecleaner, it
must be removed, cleaned and oiled every25 hoursof
operation, or more under extremely dusty conditions.
1. To clean precleaner,wash inwater and detergent
(Figure
6). Removeexcesswater by squeezinglike
a sponge and allowtodry thoroughly.Distributetwo
tablespoonsof SAE
30 engine oilevenlyaround the
precleaner. Knead into and wring excess oil from
precleaner.
7-5