Onan NHC Series Instruction Manual

DOGDDD
OPERATOR S/SERVICE MANUAL
AND PARTSCATALOG
FOR
SERIES
NHC-NHCV
INDUSTRIAL ENGINES
940-0404 11B74
Replaces 2A73
Printed inU.S.A.

INTRODUCTION
THIS OPERATOR'S MANUALCONTAINSINFORMATION
PERTAINING TOTHE OPERATION ANDMAINTENANCEOF
YOUR UNIT.
WE SUGGEST YOU KEEP THEMANUALANDTHEWIRING
DIAGRAMWHICH ACCOMPANIES EVERY UNIT AND REFER
TO ITWHENMAKINGEQUIPMENTADJUSTMENTSOR
ORDERING PARTS. ADDITIONAL COPIES ARE AVAILABLE
FOR A NOMINAL CHARGE FROMYOURDISTRIBUTOR.
WHENORDERING PARTS, REMEMBERTOINCLUDETHE
MODEL, SPECIFICATION LETTER, AND SERIAL NUMBER
LOCATED ONTHE UNIT NAMEPLATE. THISIS ESSENTIAL
TO ENSURE THE CORRECT PARTIS SHIPPED TOYOU.
FOR REPAIR SERVICE, CONTACTYOURAUTHORIZED
SERVICE REPRESENTATIVE.
WARNING
TO AVOID POSSIBLE PERSONAL INJURY OR
EQUIPMENT DAMAGE, AN AUTHORIZED SER-
VICE REPRESENTATIVE MUST PERFORM ALL
SERVICE.
t. -M

GENERAL [NFORMATION
Thismanualcontainsinstallationandoperationin-
structionsaswellasinformationrequiredforproper
maintenance,adjustmentandrepairoftheengine.
Sincethefirstandmostimportantpartofrepairwork
isthecorrectdiagnosisofthetrouble,a
troubleshootingchartisincluded.
Studyandfollowtheinstructionscarefully.Proper
serviceandmaintenancewillresultinlongerengine
lifeandbetterperformance.
How to interpret MODEL and SPEC NO.
NHC- MS/ 123A
1 34
1. Factorycodeforgeneralidentificationpurposes.
2. SpecificType:
S—MANUALstarting
MS—ELECTRICstarting
3.Factorycodeforoptionalequipmentsupplied.
4. Specification(SpecLetter)advanceswithfactory
productionmodification.
TABLEOFCONTENTS
TITLEPAGE
GeneralInformation1
SafetyPrecautions2
Specifications3
DimensionsandClearances4
AssemblyTorquesandSpecialTools5
EngineTroubleshooting6
Installation7
Operation11
PeriodicMaintenance13
FuelSystem16
GovernorSystem22
IgnitionSystem24
Battery Charging System 27
StartingSystem30
EngineDisassembly.., ' 35
PartsCatalog43
EngineWiringDiagrams66
MANUFACTURER'S GENERAL
WARRANTY
ManufaciurcrolcrJiloihcoriginalpurcha^rofGoodsfoiuse.ihcfollowins
warranties,subjectlothenualificaiionsindicated:
l.lManufaciurcr»„ranissaiislacioiyperformancefora periodotonef 11 yearfromlhe
daleeachproductisplacedinservice,solongassuchproduclisinstalled,operatedand
servicedinaccordancewilhManufaetuier'swritteninstroctions.I H I.SWAKKANY
•ISIN11EUOFALI.OTIIERWARRANTIES.EXPRESSKUORIMPLIED.
INCLUDINGFITNESSFORA PARTICULARPURPOSE.
IblManufaciurcr'sliabililyandpurchasers'soleremedyfora failureofGoodstoperform
aswarranted,andforanyandallolherclaimsarisingoutofthepurchaseanduseofthe
GoodsincludingnegligenceonlhepariofManufacturer,shallbclimitedtotherepair
orreplacementofGoodsreturnedtoManufacturer'sfactor,'oroneofitsAuihori/ed
ServiceSialions.iransportationprepaid.Thecostofanylaborincludedshallbeas
sneciHedinManufacturer'swritienittstruciions.MANUFACTURERSHALLIN
NOEVENTBELIABLEFORINCIDENTALORCONS60UENTIAI.
DAMAGES.
I'lAII claimsshallhebroughttoManufacturer'saiicntionwilhinThiny(JOIdaysafter
discoverythattheGoodsfailedtoperformaswarranted,hulinnoeventshalla cla.n
:cepiedafterone(I)yearfromthedatesuchproductisplacedinservice.
Nopersonisauthoriredtogiveanyotherwarranlyortoassumeanyolherliabilityon
Manufacturer'sbehalfunlessmadeorassumedinwritingbyanOfficerof
Manufaciurcr..andnopersonisauihoriredlogiveanywarrantyorassumeany
liabilitiesontheManufaciurcr'sbehalfunlessmadeorassumedinwritingbysuch
Manufacturer.
IMPORTANT! RETURN WARRANTY CARD ATTACHED TO UNIT.

Thefollowingsymbolsinthismanualsignalpoten-
tiallydangerousconditionstotheoperatororequip-
ment.Readthismanualcaretully.Knowwhenthese
conditionscanexist.Then,takenecessarystepsto
protectpersonnelaswellasequipment.
WARNINGlOnan uses thissymbol
1throughoutthismanualto
warnof possible serious personalinjury.
^^y^jgg This symbolrefersto possible
equipmentdamage.
Fuels/electricalequipment,batteries,exhaustgases
andmovingpartspresentpotentialhazardsthatcould
resultinserious,personalinjury.Takecareinfollow-
ingtheserecommendedprocedures.
•UseExtremeCautionNear Gasoline, Gaseous
•Fuel And Diesel Fuel. A constantpotentialex-
plosive or fire hazard exists.
Donottillfueltanknearunitwithenginerunning.
Donotsmokeoruseopenflameneartheunitor
thetueltank.
Besureallfuelsupplieshavea positiveshutoff
valve.
Fuellinesmustbeofsteelpiping,adequately
securedandfreefromleaks.Donotusecopper
pipingonflexiblelinesascopperbecomes
hardenedandbrittle.Useblackpipeonnatural
gasorgaseousfuels,notongasolineordiesel
fuels. Pipingattheengineshouldbeapproved
flexibleline.
Havea fireextinguishernearby.Besureex-
tinguisherisproperlymaintainedandbefamiliar
withitsproperuse.ExtinguishersratedABCby
theNFPAareappropriateforallapplications.
Consultthelocalfiredepartmentforthecorrect
typeofextinguishertorvariousapplications.
•GuardAgainst Electric Shock
Removeelectricpowerbeforeremovingprotec-
tiveshieldsortouchingelectricalequipment.Use
rubberinsulativematsplacedondrywoodplat-
formsoverfloorsthataremetalorconcretewhen
aroundelectricalequipment.Donotweardamp
.clothing(particularlywetshoes)orallowskin
surfacestobedampwhenhandlingelectrical
equipment.
Jewelryisa goodconductorotelectricityand
shouldberemovedwhenworkingonelectrical
equipment.
Useextremecautionwhenworkingonelectrical
components.Highvoltagescauseinjuryordeath.
Followallstateandlocalelectricalcodes.Haveall
electricalinstallationspertormedbya qualified
licensedelectrician.
•DoNotSmokeWhile Servicing Batteries
Leadacidbatteriesemita highlyexplosive
hydrogengasthatcanbeignitedbyelectrical
arcingorbysmoking.
• Exhaust Gases Are Toxic
Provideanadequateexhaustsystemtoproperly
expeldischargedgases.Checkexhaustsystem
regularlytorleaks.Ensurethatexhaustmanifolds
aresecureandnotwarped.
Besuretheunitiswellventilated.
• Keep TheUnitAndSurroundingArea Clean.
Removealloildeposits.Removeallunnecessary
greaseandoilfromtheunit.Accumulatedgrease
andoilcancauseoverheatingandsubsequent
enginedamageandmaypresenta potentialfire
hazard.
Disposeofoilyrags.Keepthefloorcleananddry.
•ProtectAgainst Moving Parts.
Avoidmovingpartsoftheunit.Loosejackets,
shirtsorsleevesshouldnotbepermittedbecause
otthedangerofbecomingcaughtinmoving
parts.
Makesureallnutsandboltsaresecure.Keep
powershieldsandguardsinposition.
Ifadjustmentsmustbemadewhiletheunitis
running, useextremecautionaroundhot
manifolds,movingparts,etc.
Donotworkonthisequipmentwhenmentallyor
physicallyfatigued.

SPECIFICATIONS
NumberofCylinders2
_ Displacement(cubicinch)60
CylinderBore0 .:• 3-9/16in.
PistonStroke• • • 3 inch
Horsepower—NHC(PressureCooled)25BHP@ 3600rpm
Horsepower—NHCV(Vacu-FloCooled)22.5BHP@ 3300rpm
CompressionRatio7.0to1
VentilationRequired(cfm@ 3600rpm)NHC1080
(cfm@ 3600rpm)NHCV1200
OilCapacity3-1/2quart
OilCapacitywithFilterChange•••4 quart
Starting' Electric
Ignition• Battery
CombustionAir(cfm@ 3600rpm): 80
Fuel• • Gasoline(regulargrade)
FuelPumpDiaphragm,4 ft.lift
Battery12Volt
TUNE-UP SPECIFICATIONS
SparkPlugGap• 025-inch
.BreakerPointGap••.016-inch
IgnitionTiming(Fixed),ElectricStart.Units••...20°BTC
Tappets(Cold)Intake..;.003-inch
Exhaust; 012-inch

DIMENSIONSAND CLEARANCES
Allclearancesgivenatroomtemperatureof70°F.
Alldimensionsininchesunlessotherwisespecified. MinimumMaximum
ValveSteminGuide—Intake0.0010 u.OO^b
ValveSteminGuide—Exhaust0.00250.0040
ValveSpringLength
FreeLength1.662
CompressedLength1.375^j.
ValveSpringTension(Ib.)
Open
Closed
ValveSeatBoreDiameter
Intake
Exhaust
ValveSeatDiameter
Intake
Exhaust
ValveStemDiameter
Intake
Exhaust
ValveGuideDiameter(I.D.)
ValveLifterDiameter
ValveLifterBore
ValveSeatInterferenceWidth
ValveFaceAngle
ValveSeatAngle
ValveInterferenceAngle
CrankshaftMainBearing
CrankshaftEndPlay
CamshaftBearing
CamshaftEndPlay
CamshaftLift
CamshaftBearingDiameter
CamshaftJournalDiameter
RodBearing(ForgedRod).-•
ConnectingRodEndPlay(DuctileIron)
TimingGearBacklash
OilPumpGearBacklash
PistontoCylinder,StrutType(Measuredbelowoil-controlling ring—
90°frompin)Clearance
PistonPinDiameter
PistonPininPiston
PistonPininRod.•
PistonRingGrooveWidth
TUP1 :
Top2
Top3
PistonRingGapinCylinder
PistonRingSideClearance(Topcompressionringonly)
CrankshaftMainBearingJournal—StandardSize
MainBearingDiameter:
MainBearingClearance
CrankshaftRodBearingJournal—Standai'dSize
CylinderBore—StandardSize
71 79
38 42
1.5645 1.5655
1.2510 1.2520
1.569 1.570
1.255 1.256
0.3425 0.3430
0.3410 0.3415
0.344 0.346
0.7575 0.7480
0.7505 0.7515
1/32 3/64
44"
45°
1°
0.0025. 0.0038
0.005 0.009
0.0015 0.0030
0.003 —
0.3UO
1.3760 1.3770
1.3740 1.374b
0.0005 0.0023
0.002 0.016
0.002 0.003
0.002 0.005
0.0015 0.0035
0.7500 0.7502
ThumbPushHI
0.0001 0.0005
0.0955 0.0965
0.0955 0.0965
0.1880 0.1890
0.010 0.020
0.006
1.9992 2.0000
2.0015 2.0040
0.0015 0.0043
1.6252 1.6260
3.5625 3.563b

ASSEMBLY TORQUES
TORQUES
Assemblytorquesasgivenhererequiretheuseofa
torquewrench.Theseassemblytorqueswillassure
propertightnesswithoutdangerofstrippingthe
threads.Ifa torquewrenchisnotavailable,youwill
have.toestimatethedegreeoftightnessnecessaryfor
the stud, nutorscrewbeinginstalledandtighten
accordingly.Becarefulnottostripthethreads.Check
allstuds,nutsandscrewsoftenwiththeengine cold.
Tightenasneededtopreventthemfromworking
loose.
TORQUESPECIFICATIONSFt.-Lb.
CylinderHeadNuts17-19
RearBearingPlate25-28
ConnectingRodBolt27-29
FlywheelCapscrew35-40
StarterMountingBracketto
OilBaseScrews43-48
GearCaseCover8-10
OilPump7-9
Other3/8CylinderBlockNuts18-23;.
IntakeManifold18-20
ExhaustManifold10-12
SPECIAL TOOLS
SPECIAL TOOLS
ThesetoolsareavailablefromOnantoaidserviceand
repairwork.
CrankshaftGearPullingRing.420-0248
FlywheelPuller...420-0100
CombinationBearingRemover,
MainandCam420-0325
CombinationBearingDriver,
MainandCam420-0324
ValveGuideDriver420-0300
ValveSeatDriver420-0308
ValveSeatStaker
Intake: 420-0309
Exhaust420-0310
ValveSeatCutter420-0311
OilSealGuideandDriver
BearingPlate420-0181
GearCover420-0313
TimingAdvanceMechanism
CoverDriver420-0296
PistonRingSpreader420-0146
PistonGrooveCleaner420-0332

STARTINGSYSTEM
s
LooseorCorrodedBatteryConnection
a • LoworDischargedBattery
•
FaultyStarter
•
FaultyStartSolenoid
IGNITIONSYSTEM
• • • • e
IgnitionTimingWrong
o • •
WrongSparkPlugGap
e • •
WornPointsorImproperGapSetting
• • •
BadIgnitionCoilorCondenser
• •
FaultySparkPlugWires
• e j
OutofFuel- Check
• • • s • •
LeanFuelMixture- Readjust
t e • a e
RichFuelMixtureorChokeStuck
• c • 9
EngineFlooded
e • • • • •
PoorQualityFuel
• •
0
• •
DirtyCarburetor
• • • • • • a •
DirtyAirCleaner
• • •
DirtyFuelFilter
• • • •
DefectiveFuelPump
INTERNALENGINE
• • • • •
WrongValveClearance
• • a • •
BrokenValveSpring'
a • • • •
ValveorValveSealLeaking
* • • e
PistonRingsWornorBroken
• a • • •
WrongBearingClearance
COOLINGSYSTEM(AIRCOOLED)
• •
PoorAirCirculation
• •
DirtyorOilyCoolingFins
• • • •
BlownHeadGasket
-COOLING'SYSTEM (WATERCOOLED)
•
InsufficientCoolant
ft
•
FaultyThermostat
• •
WornWaterPumporPumpSeal
•
WaterPassagesRestricted
•
DefectiveGaskets
• • • • • •
BlownHeadGasket
, - LUBRICATIONSYSTEM
• •
DefectiveOilGauge
• •
ReliefValveStuck
• • • • • a •
FaultyOilPump
e • • a • •
DirtyOilorFiIter
• • • • • • • • a •
OilTooLightorDiluted
o • • • • a a •
Oi 1 LevelLow
• •
OilTooHeavy
• • • •
DirtyCrankcaseBreatherValve
THROTTLEANDGOVERNOR
• •
LinkageOutofAdjustment
•
LinkageWornorDisconnected
•
GovernorSpringSensitivityTooGreat
•
LinkageBinding

INSTALLATION
Thetypeofinstallationcanaffectthe . lifeofthe
engine,thecostofoperationandthefrequencyof
necessaryservice.Plantheinstallationcarefullyto
ensurethebestperformance.
Becauseofthegreatvarietyofuses,andthemany
variationsoftheengine,theseinstallationinstruc-
tionsaretypicalorgeneralinnature.Usethe
installationrecommendationsgivenasa general
guide.
MOUNTING
Thereareseveralacceptablemethodsof.mounting
theengine.Amongfactorstobeconsideredare:
location, methodofcouplingtheenginetothe load,
typeoffoundationorsupport,etc.Theengineshould
bemountedona levelsurfaceifpossible.Maximum
operationangleis15degreessideways,30degrees
fronttoreartilt.Iftheengineistooperateatanangle, •
besuretore-marktheoillevelindicatortocompen-
sateforthetilt.
AIR OUT
VENTILATION
Theenginemustbeprovidedwithasupplyoffreshair
forcoolingandforcombustion.
PressureCooledEngine:Positiontheairinletopen-
ingdirectlyinfrontoftheengineandasclosetothe
engineblowerwheelaspossible.Theareaoftheinlet
shouldbenotlessthan80squareinches.Iflouversor.
grillworkereused,increasetheareatocompensate
forthereducedairflow.Provideextraventilationifthe
drivenloadgeneratesheatduringoperation.
Theheatedairoutletmustallowtheheatedairto
escapefreelyandpreventrecirculationwiththe
coolingair.A ductbetweenthecompartmentairinlet
andtheengineblowerhousingmaybenecessary.
Locatetheairoutletoppositetheintakeoratleastata
90degreeangle.Theareaoftheoutletshouldbeat
least15percentlargerthanthatoftheinlet.Allow
sufficientroomonallsidestopermitaccessfor
servicing.
FIGURE1.AIRFLOWTHROUGHVACU-
FLOSYSTEM
Vacu-F!oCooledEngine:Thevacu-floequipped
engineusesanintegralflywheel-centrifugalfanto
pullcoolairintotheengineshroudandoverthe
coolingfinsandsurfacesoftheengine,Figure1.The
heatedairisdirectedthroughanairtightscrollwhich
encasestheflyvyheelfan.Thescrollmaybeposition-
edtodischargeheatedairinthedownward,upward,
leftorrightdirection.Thisispossiblebecausethe
backsectionofthescroll(Figure2)hasfouridentical
holesshapedtofitoverthe<endofthestartermotor.
Thescrolloutlethasa mesh-typescreenforsafety.
OpenAirInstallation:Forinstallationswherethe
engineisoperatedoutside,ventilationwillbeno
problem..However,inprotectingtheenginefromthe
elements,seethatnothingobstructstheflowofair
aroundtheengine.
Theoutletofthevacu-floscrollmustnotbe
restrictedoroverheatingwillresult.Engine
overheatingcancausetroublesrangingfromvaporlocktoscored
pistonsandcylinders.

SCROLLBAC
SCROLL
Iftheductlengthexceeds5feet,increaseductsize30
percent.Usenomorethantwo90degreeradius-type
(notsquare-type)elbowsifitisnecessarytochange
airflowdirection.Whena ductisusedbetweenthe
scrolldischargeandtheoutletvent,itsunobstructed
airflowareamustbeatleastaslargeasthescroll
discharge.Thecross-sectionalareaoftheductmust
beincreasedifairflowisrestrictedbybends,long
runs, screensortheexhaustpipe.Exhaustpipes
runninginsideVacu-Floductsshouldbecoveredwith
asbestostape.
WARNING\ Thesafetyscreenusedtocoverventsmustbe
••irii™««—I 1/4-inch meshorlargertopermitsufficientair
flow,andmustbecommensuratewithsafetystandardsfor
hazardousmovingpartstoavoidpersonalcontact.Providea short
canvassectionbetweentheengineairoutletandtheexternalduct
oropening,toabsorbvibration.Ifoperationincoldweatheris
likely,installinga shutterintheairoutletisadvisable.Coldweather
cancauseovercoolingifairflowisnotregulated.
EXHAUST
^ARNJINGJExhaustgasesaretoxic.Provideanadequate
exhaustsystemtoproperlyexpelexhaust
gases.Checkexhaustsystemregularlyforleaks.Ensurethat
exhaustmanifoldsaresecureandnotwarped.Besuretheunitis
wellventilated.
FIGURE2. VACU-FLOSCROLL
POSITIONS
Shoulda vacu-floenginechronicallyoverheat,the
mostlikelysourcesoftheproblemare:
1. Airinletisobstructedortoosmalltoallowproper
ventilation.
2. Airdischargeopeningispartiallyblockedby
externalductsorexhaustsystems.
3.Recirculationofheatedairintofreshairinlet.
Thevacu-floinstallationpermitsgreaterfreedomin
choiceoflocatingtheairinletandoutletopenings,
andpermitstheuseofa compartmentonlyslightly
largerthantheengineitself.
60
Theareaoftheairinletmustbeatleast/TWsquare
inches.Ifa filter,grille,orlouversareuseflTtheinlet
openingmustbeincreasedaccordingly.Theair
outletopeningshouldbelocatedasclosetothe
engineaspossible.
Usea lengthofflexibletubingbetweentheengine
exhaustoutletandanyrigidpipingtoabsorbengine
vibration. Shieldthelineifitpassesthrougha
combustiblewallorpartition.Ifturnsarenecessary,
usesweepingtype(longradius)elbows.Increaseone
pipesize(frommanifoldoutletsize)foreachad-
ditionaltenfeetinlength.Locatetheoutletawayfrom
theairintake.
CARBURETOR AIRINTAKE
Properengineefficiencydependsupona supplyof
freshairtothecarburetor.Underspecialconditions,
itmaybenecessarytomovetheaircleaneroffthe
engine,usinga longerconnectionhoseasnecessary.
Forextremelydustyordirtyconditions,installa
specialheavydutyaircleaner.
FUEL SYSTEM
Theengineuseseithera diaphragmorpulsating
diaphragmtypefuelpump.Thefuelpumphasa 1/8-
inchpipethreadedinlet,fittedwitha 1/4-inch inverted
flaretubefitting.If a solidwalllineisused,forma loop
intheline,orinstalla sectionofflexiblefuelhose,to
absorbvibration.Ifa linewitha pipethreadendis
used, removetheflaretypefittingfromthefuelpump
inlet.

Thefuelsupplytankmaybeinstalledinanysafe,
convenientlocation.Ifthetankisinstalledwithinthe
engineenclosure,providea ventlinetotheoutsideof
theenclosure.
Theinstallationofa fuelfilterbetweenthefueltank
Sndthefuelpumpis'recommended.Thefuelfilter
shouldbefittedwitha shutoffvalveandshouldbe
easilyaccessibleforcleaning.
CONNECTING TOTHE LOAD
Thedimensionsofvariouspowertakeoffshaftsareas
follows:
SHAFT DIAMETER LENGTH KEYSIZE
STD
1-7/16
3-1/16
3/8
RockfordClutch
1-7/16
3.-1/16
3/8
GearReduction 1-1/4 2-3/4-1/4
BeltDrive:V-beltsarepreferabletoflatbelts.Consult
areliablebeltingsupplierforrecommendations
regardingsizeofpulleys,numberofbelts,etc.
required. A typicalbeltdriveinstallationisshownin
Figure3.
KEEPSHAFTSOFENGINE
ANDLOADPARALLEL.
BELTINTIGHTENED
POSITION- PULLING
LOAD
ENGINE
PULLEY
BELTINLOOSENED
POSITION- NOT
PULLINGLOAD-
KEEPPULLEYSALfGNEt
WITHEACHOTHER
IDLERPULLEY
LOAD
PULLEY
BRACKETTOKEEP
BELTOFFENGINE
PULLEY
FIGURE3.DRIVEBELTINSTALLATION
Complywiththefollowinginstallationrequirements:
1. The.shaftsoftheengineandtheloadmustbe
parallelwitheachother.
2. Thepulleysoftheengineandtheloadmustbein
alignment.
3.Mount.theenginepulleysasclosetotheengineas
possible.
4. Iftheinstallationpermits,beltsshouldrun
horizontally.
5.Somemethod'ofdisconnectingtheloadfor
startingisrecommended.Ifa clutchisnotused,a
belt-tighteneridlerarrangementcanbeused.
FlexibleCoupling:^lfa flexiblecouplingengine-to-
loaddriveisused,theloadshaftmustbeinlineand
centeredwith-theengineshaft(Figure4).
ENGINEPOWER
TAKE-OFF^
SHAFT FLEXIBLE
COUPLING
FIGURE4.FLEXIBLECOUPLING
ReductionGearDrive:Reductiongeardrivesare
mountedatthefactory(whenordered).Themethod
ofconnectingtheloadisthesameaswhenconnec-
tingdirectlytotheengineshaft.
ClutchInstallation:A RockfordClutchcanbein-
stalledatthefactoryorinthe field. Installtheclutch
accordingtothefollowinginstructionsandFigure5.
KEYWAY
DRILL13/64"HOLE'
1/8"DEEP
CRANKSHAFTSTUBSHAFT
CLUTCHCLUTCH
ASSEMBLYHOUSjNG
I1/32"
A867 SETSCREW POWER
TAKE-OFF
SHAFT
FIGURE5.CLUTCHINSTALLATION

Provideroomfortheclutchadaptercastingby
pluggingthewetholeswith a 3/8-16x 1/2-inch slotted
headlesssetscrew.Applysealingcompoundtothe
threadsandinstallscrewflushwiththecylinder
block.
Drilla 13/64-inchhole(orfiledslot)inthecrankshaft
for.theclutchsetscrew.Locatecenterofhole11/32-
inchfromtheendanddirectlyoppositethekeywayin
thecrankshaft.
Installtheclutchadapter,withdrainslotdownward,
usingtwocapscrews3/8-16x 2-inchesonthelower
andonecapscrew3/8-16x 1 -3/4-inchontheupper#2
cylinderside(cylindernearerclutch).Installthe3/8x
3-7/8-inchstudthroughtheadapterintotheengine
blockupperremaininghole.Usea lockwasheron
eachassemblyscrew.Usea flatwasheranda lock
washerunderthestudnut.
Installthecrankshaftkey.Removetheclutchset
screw.Installtheclutchassembly(lesshousing)to
thecrankshaft,drivingitoncarefullywithasoft-faced
hammeruntilsetscrewholeisaligned.Installset
screwtobottomincrankshafthole,thenbackitout
onefull turn. Tightenclutchretainingscrewsuntil
clutchisclampedsecurelytocrankshaft.Lockthe
screwsandtightenthesetscrew.
Applygreasetosplinedpowertakeoffshaft.-Position
theclutchthrow-outtoalignthegreasefittingwith
theholeinthehousing (#1 cylinderside,horizontal).
Pullthethrow-outcollaroutwardtoremovetension.
Installtheclutchhousingsothattheclutchthrow-out
forkengagesthethrow-outcollar.Besurethe
serratedshaftisproperlymeshedwiththeclutch-
plate. Usetwocapscrews7/16-14x 2-inchesonthe
lowerandonecapscrew7/16-14x 1-3/3-inch onthe
upper#2cylinderside.Installthestudwasherand
nut.Lubricatethetwogreasefittingsjustuntilgrease
appears.
BATTERY CONNECTIONS (Engines with
AutomotiveTypeSeparateStarter)
Connectthe12voltbatterypositivecabletothe
enginestartswitchterminal.Connectthebattery
negativecabletothegroundpointontheengineoil
base(Figure6).
BATTE
POSITIV
CABLE
IVE
CABLE
(FASTENUNDERCONVENIENT
BOLTONENGINE)
FIGURE6.BATTERYCONNECTIONS
10

BEFORE STARTING
CrankcaseOil:Besurethecrankcasehasbeenfilled
withoiltothe"FULL"markontheoillevelindicator.
UseoilwiththeAPI(AmericanPetroleumInstitute)
designationSEorSE/CC.Donotuseanoilwiththe
designationCDunlessitisalsodesignatedSEand
theoilmanufacturercertifiesitwillperformsatisfac-
torilyingasolineengines.
RecommendedFuel:Useclean,regulargrade,
automotivegasoline.Donotusehighlyleaded
premiumtypes.
Fornewengines,themostsatisfactoryresultsare
obtainedbyusingnonleadedgasoline.Forolder
enginesthathavepreviouslyusedle'adedgasoline,
headsmustbetakenoffandallleaddepositsremoved
fromenginebeforeswitchingtononleadedgasoline.
Ifleaddepositsarenotremovedfromengine
beforeswitchingfromleadedtononleaded
gasoline,preignitioncouldoccurcausingseveredamagetothe
engine.
WARNING j Neverfillthetankwhentheengineisrunning.
Leavesomespaceinthetankforfuelexpan:
sion.
Openthefuellinevalve(whenused)andoperate
primertoassurefuelsupplyafterfillinganempty
tank.
STARTING (Electric Start)
1. MoveignitionswitchtoitsONposition.
2. PushSTARTbuttontocrankengine.
Iftheenginefailstostartatfirstattempt,inhibitoroil
usedatthefactorymayhavefouledthesparkplugs.
Removetheplugs,cleaninsuitablesolvent,dry
thoroughlyandinstall.Heavyexhaustsmokewhen
theengineisfirststartedisnormalandiscausedby
inhibitoroil.
APPLYING LOAD
Whenapplyingtheloadtoa neworreconditioned
engine,itshouldbeappliedgraduallyinaboutfour
steps; eachstepofnotlessthan30minutesrunning
time. Startwith1/4 load, then1/2,3/4andfull load.
BATTERY CHARGING
Thebatterychargerateiscontrolledbya charge
regulator.Theregulatorissettoallowtheproperrate
ofchargeatoperatingspeed.
STOPPING THE ENGINE
Disconnectallloadbeforestoppingtheengine.
Enginesequippedwithbatteryignitionarestopped
bypositioningtheignitionswitchtotheOFFposition.
HIGHTEMPERATURES-
1. Seethatnothingobstructs ai r flowtoandfromthe
engine.
2. Keepcoolingfinsclean.Airhousingshouldbe
properlyinstalledandundamaged.
LOW TEMPERATURES
1. UsecorrectSAENo.oilfortemperature con-
ditions.Changeoilonlywhenengineiswarm.
2. Usefresh fuel. Protectagainstmoistureconden-
sation.
3.Keepfuelsystemcleanandbatteriesina well
chargedcondition.
4. Partiallyrestrictcoolairflow,butusecareto
avoidoverheating.
STARTING (Manual Start)
1. Holdchokeaboutthreequarterwayclosedoras
necessaryaccordingtotemperatureconditions.
2. Pullstartropewitha faststeadypulltocrank
engine.Donotjerk.
3.Openchokeasenginewarmsup.
DUST ANDDIRT
1. Keepunitclean.Keepcoolingsystemclean.
2. Serviceaircleanerasfrequentlyasrequired.
3.Changecrankcaseoilandfiltermoreoftenthan
recommendedundernormalconditions.
4. Keepoilandgasolineindusttightcontainers.
5.Keepgovernorlinkageclean.
11

HIGH ALTITUDE
Foroperationataltitudesof2500feetormore,close
thecarburetormainjetadjustmentslightlytomain-
tainproperair-to-fuelratio.RefertotheFuelSystem
section. Maximumpowerwillbereducedabout4
percentforeach1000feetincreaseinaltitude.
PROTECTION FOR EXTENDED OUT-OF-
SERVICE PERIOD
Protectanenginethatistobeout-of-serviceformore
than30daysasfollows:
1. Runengineuntilthoroughlywarmedup.
2. Turnofffuelsupplyandrununtilenginestops
fromlackof fuel.
3.Drainoilfromoilbasewhilestillwarm.Attacha
warningtagtorefillbeforeoperation.
4. Removeeachsparkplug.Pouroneounce(two
tablespoons)ofrustinhibitor(orSAE#50)oilinto
cylinder.Crankengineovera fewtimesto
distributeoilfilmoncylinderwallsandrings.
Reinstalleachsparkplug.
5.Serviceaircleanerpermaintenanceschedule.
6.Lubricategovernorlinkage.Protectagainstdust,
etc.bywrappingwitha cleancloth.
7.Plugexhaustoutlettoprevententranceofbugs,
moisture,ordirt.
8.Wipeentireunitclean.Coatpartslikelytorust
witha lightfilmofgreaseoroil.
9.Providea suitablecoverforentireunit.
10. Disconnectbatteryandfollowstandardbattery
storageprocedure.
CAUTION) Dischargedbatteriesaresubjecttosevere
damageifexposedtofreezingtemperatures.
Storeallbatteriesina fullychargedconditionandmaintaincharge
duringstorage.
RETURNING THESETTO OPERATION
1. CHECKSERVICEIDENTIFICATIONTAGSto
properlyservicetheengine.
2. Uncoverandremoveallstoragesealsfrom
engine.Removeanydust,dirt,orforeignmatter.
3.CHECKfuelsupplytanksformoistureac-
cumulations(draintanksifnecessary).CHECK
lubricatingoilformoistureorcontamination
(drainifnecessary).CHECKfuellineconnec-
tions, allwiringconnections,andexhaustline
connections.
4. Serviceaircleaner.Bleedfuelsystem(ifmoisture
orcontaminationarefoundin fuel, replacefilters
andcleanfuelpumpsedimentbowl).
5.Checktagonoilbaseandverifythatoilviscosity
isstillcorrectforexistingambienttemperature.
6.Cleanandcheckbattery.Measurespecificgravity
(1.260at25°C [77°F])andverifyleveltobeat
split ring. Ifspecificgravityislow,chargeuntil
correctvalueisobtained.Iflevelislow,add
distilledwaterandchargeuntilspecificgravityis
correct.DONOTOVERCHARGE..
"WARNINGk Dosmokewhileservicingbatteries.
Explosivegasesareemittedfrom
batteriesinoperation.Ignitionofthesegasescancause
severepersonalinjury.
7.Checkengineforfueloroilleaks.Correctleakage
asrequired.
8.Installfullychargedbatteries.
9.Startengineandcheckwhilerunningforleaks,
correctvoltageoutput,andpropercooling.
Afterenginehasstarted,excessivebluesmokewillbeexhausted
andtheenginewillrunroughuntiltherustinhibitororoilhas
burnedaway.
12

PERIODIC MAINTENANCE
TABLE 1. PERIODIC MAINTENANCE SCHEDULE
SERVICETHESEITEMS AFTEREACHCYCLEOFINDICATEDHOURS SERVICETHESEITEMS 8 50 100 200 500 1000 5000
*InspectEngineGenerally X
"CheckFuelSupply X
CheckOilLevel X
CleanGovernorLinkage X*
ChangeCrankcaseOil xl X*
CheckBreakerPoints X
CheckBatteryElectrolyteLevel X
CleanFuelFilter X
CheckSparkPlugs X
ReplaceOilFilter X*
ReplaceAirCleaner X*
RemoveDeposits.in.CombustionChamber X
CheckValveClearance xl•• X
InspectValves,GrindifNecessary .X
CompleteReconditioning X
*- Checkforexhaustleaks,fuelleaks,propermounting,etc.
X*- Performmoreoftenunderdustyorextremecoldweatherconditions.
X-1- Recommendedintervalinhotweatherorheavilyloadedconditions.
PERIODICMAINTENANCESCHEDULE
Regularlyscheduledmaintenanceisthekeytolower
operatingcostsandlongerservicelifefortheunit.
Theschedule(Table-1)canbeusedasa guide.
However,actualoperatingconditionsunderwhicha
unitisrunshouldbethedeterminingfactorin
establishinga maintenanceschedule.When
operatinginverydustyordirtyconditions,someof'
theserviceperiodsmay.havetobereduced.Check
theconditionofthecrankcaseoil,thefilters,etc.
frequentlyuntiltheproperservicetimeperiodscanbe
established.Whenanyabnormalitiesoccurin
operation—unusualnoisesfromengineor
accessories,lossofpower,overheating,etc.—
contactyourOnandealer.
CAPANDOIL
LEVELINDICATOR
KEEPOIL
ATTHISLEVEL.
NEVEROPERATE
ENGINEWITHOIL
BELOWTHISLEVEL.
A874
-FULL
ALWAYSREPLACE
CAPTIGHTLY.OR
OILLEAKAGEMAY
OCCUR.
CRANKCASE OIL
Theoilcapacityis,3-1/2U.S.quarts(4withfilter).Fill
tothe"FULL"markontheoillevelindicator,Figure?.. FIGURE7:OILLEVELINDICATOR
13

Whenadding oil betweenchanges,always use the
samebrand and weightthat isinthe crankcase.
Variousbrands ofoil may notbe compatiblewhen
mixedtogether.
Oilconsumption maybe higherwith a multigrade oil
thanwith a singlegrade oilif both'oilshavecom-
parableviscosities at 210°F.Therefore,singlegrade
oils are generallymoredesirable,unlessanticipating
awiderange of temperatures. Usethe propergrade
oil for the expectedconditions.
OILFILTER
RIP PAN
FIGURE 8.OIL FILTERLOCATION
TEMPERATURE
•Below 0°
0° to30°
30° to90°
Above 90°
GRADE
5W
10W
30
50
Check oil leveldaily.Change oil every 100 hours
undernormaloperatingconditions.Whenoperating
inextremelydusty or dirtyconditions,change oil
moreoften.
CRANKCASEBREATHER
Theengineisequippedwitha ballcheckvalve(Figure
9) for maintainingcrankcasevacuum. No
maintenance is generallyrequired.Should the
crankcasebecomepressurized, as evidenced byoil
leaks atthe seals or around the cap of the oil level
indicator,cleanbaffle in suitablesolvent.
Clean or replacecrankcasebreatherbaffleperiodically. Be sure
bafflematerialdoesn'tcomeapart and workinto the manifold.
OILFILTER
Change the crankcase oil filterevery 200 hours.
Remove the filter(Figure 8)by .turningcoun-
terclockwise,using a filterwrench. Addthe strip
providedwith the filter to prevent air loss in the area
indicated. Itis advisable to wipe drythe drip pan
locatedbelow the filter.Coatrubbergasket on filter
with a film ofoil beforeinstalling.Install the filter
finger-tightplus 1/4to 1/2 turn. If oilbecomessodirty
that the markings ontheoil levelindicatorcannot be
seen, change the filterandshorten the filterservice
period.
BREATHER HOSE
HOSE CLAM
CAP ANO VALVE
BREATHERTUBE
FIGURE 9! CRANKCASEBREATHER
14

AIR CLEANER
TheNHCengineusesa replaceable,spin-onair
cleaner/Figure10.Removeandreplaceevery200
hours.
CAUTION
causeseveredamagetoengineparts.
Donotrunenginewithaircleanerremoved.
Intakeofdirtyairorsolidmaterialscould
AIR
CLEANER
FIGURE10.AIRCLEANER
GOVERNOR LINKAGE
Thelinkagemustbeabletomovefreelythroughits
entiretravel.Every50.hoursofoperationcleanthe
metaljointsasshowninFigure11.Alsoinspectthe
linkageforbinding,excessiveslackandwear.
Cleanandlubricatemetalballjoints.Don'tlubricateplasticjoint^
KEEP
GOVERNOR
LINKAGE
LUBRICATED
REDUCTION GEAR DRIVE
Drainthegearboxafterthefirst100hoursof
operationandrefillwithfreshlubricantofthe
recommendedgrade.Repeatthisprocedureeverysix
monthsthereafter,orevery100hours.
UseonlySAE50motoroilorSAE90mineralgearoil.
Donotuselubricantscommonlyknownasextreme
pressurelubricants,hypoidlubricants,etc.
Maintaintheproperoillevelbetweenchanges.Over-
fillingwillcausefoaming,whichcanleadtoanoilleak
duetooverheating.Removethefillerplugontopof
thecaseandtheoillevelplugfromthefaceofthegear
case. Fillthecaseuntiltheoiljustbeginstoflowfrom
theoillevelplughole.Gearboxholds1/2pintU.S.
measure.Replacebothplugs.SeeFigure12.
VENTPLUG
FILLWITHOILTO
LEVELOFHOLE
FIGURE12.REDUCTIONGEARDRIVE
EXHAUST SYSTEM
Makeregularinspectionsoftheexhaustsystem
throughouttheentirelifeoftheengine.Locateleaks
inmufflerandpipingwhiletheengineisoperating.
Repairallleaksimmediatelyaftertheyaredetected
forpersonnelsafety.
WARNING Leakyexhaustsystemsemitnoxiouscarbon
monoxidefumeswhicharea potentialsafety
FIGURE11.GOVERNORLINKAGE
hazardinenclosedareas.
BATTERY
Checkchargecondition.Checkelectrolyte level. Add
distilledwatertokeepelectrolyteatitsproperlevel.-In
freezingweather,runengineimmediatelyafterad-
dingwater.Keepbattery.connectionstightandclean...
15

FUEL SYSTEM
GASOLINE CARBURETOR
Forcorrectionofproblemstracedto,the,gasoline
carburetor,usetheappropriateproceduresselected
fromthefollowingsequence,referringtoFigures13
and14.
AdjustmentUnderLoad:Adjustthecarburetoras
followswhena fullloadcanbeapplied.
1. Makesuretheignitionsystemisworkingproperly
andthatthegovernorisadjusted.
2. Starttheengineandallowittowarmup.Ifthe
carburetorissofaroutofadjustmentthatthe
enginewillnotstart,closebothneedlevalves
gentlytotheirseats.Thenopeneach1 to1-1/2
turns, firsttheidleandthenthemainadjustment.
3.Withnoloadappliedtoengine,turntheidle
adjustmentoutuntiltheenginespeeddrops
slightlybelownormal.Thenturntheneedlein
untiltheenginespeedreturnstonormal.
4. Applya fullloadtotheengineandthencarefully
turnthemainadjustmentinuntilthespeeddrops
slightlybelownormal.Turntheneedleoutuntil
theenginespeedretumstonormal.
AdjustmentUnder"NoLoad"Conditions:Whena
THROTTLE
STOPSCREW
FUELIDLE
ADJUSTMENT
A
FLOATBOWLNUT
MAINFUEL
ADJUSTMENT
B
FIGURE14.CARBURETORADJUSTMENTS
loadcannotbeapplied,adjustthecarburetoras
follows:.
1. Perform steps 1and 2 as given under Adjustment
Under Load.
2. Pulloutonthegovernormechanismtoslowthe
unitdowntoabout800to900rpm.
IDLE
ADJUSTMENTNEEDLE-
CHOKESHAFT
THROTTLEPLATE
THROTTLESHAFT
ANDLEVER
CHOKEPLATE
FLOAT
ASSEMBLY
FUELBOWL -MAINJET
ADJUSTMENT
FLOATAXLE
^SPRING
POSITIONHOOK
UNDERTANGON
FLOAT
POSITIONOFSPRING
AFTERINSTALLATION
EH
FIGURE13.CARBURETORASSEMBLY
16

3.Settheidleadjustmentscrewforevenoperation
(sotheengineisfiringonbothcylindersandis
runningsmoothly).
4. Releasethegovernormechanismtoallowthe
enginetoaccelerate.Iftheengineaccelerates
evenlyandwithouta lag,themainadjustmentis
correct.Ifnot,adjusttheneedleoutwardabout
1/4turnandagainslowdowntheengineand
releasethemechanism.Continueuntiltheengine
acceleratesevenlyandwithouta timelagafter
releasingthegovernor.
5.Withthecarburetorandgovernoradjusted,set
thethrottlestopscrewatthedesiredidlespeed.
Float-LevelCheck:Ifthecarburetoradjustmentfails
toprovidesatisfactoryoperation,removethecar-
buretorandcheckthefloatlevelasfollows:
1. Removethefuelline;aircleanerhose,governor
linkageandchokewires.
2. Removethetwocarburetormountingnutsand
removethecarburetor.
3.Unscrewthefloatbowlnutandremovetheentire
mainfueladjustmentassemblyfromthefloat
bowl.
4. Invertthecarburetorandcheckthatthefloat
surfacenearestthegasketis1/8+ 1/16-inch from
thegasket.Bendthefloattabasrequiredto
producethisspacing.
Ifthecarburetorutilizesaninternallyspringloadedfuelinlet
valve; thefloatsurfaceshouldbe1/8± 1/16-inch fromthe
gasketwiththefullweightofthefloatcompressingthespring
intheneedle.
5.Reassemble,installandtest.
6.SeeFigure15.
BENDTAB
TOADJUST
GASKETTOFLOAT
DIMENSION1/8INCH
A9I3-I
FIGURE15.FLOATLEVELADJUSTMENT
CarburetorRemovalandDisassembly:Removeand
disassemblethecarburetorassemblyasfollows,
referringtoFigure15:
1. Removethefuelline,aircleanerhose,governor
linkage,andchokewires.
2. Removethetwocarburetormountingnutsand
'removethecarburetor.
3.Removethemain.jetassemblyandbowl.'
4. Removethefloatpinandfloat.
5.Liftoutthefuelinletvalveandunscrewthevalve
seat.
6.Removetheidleadjustmentneedle.
7.Removethethrottleplatescrewsandtheplate,'
thenpull.outttiethrottleshaft.,
8.Removethechokeplatescrewsandplate,then
pulloutthechokeshaft.
CarburetorAssemblyandInstallation:Cleanthe
componentsandrepairorreplacedefectiveorworn
parts. Useacetoneoralcoholtodissolvegum
depositsifcarburetorcleanerisnoteffective.Soak
thepartsincarburetorcleaner,usingitasdirectedby
themanufacturer.Cleanallcarbonfromthecar-
buretorbowl,especiallyintheareaofthethrottle
plate. Blowoutcloggedpassageswithcompressed
air.Checktheneedles,nozzle,andfloatfordamage
orfuelloading.Checkthechokeandthrottleshafts.
Reassembleandinstallasfollows:
1. Installthethrottleshaftandplate,usingnew
screwsandlockwashers.Installwithbevelmated
tothecarburetorbody.Iftheplateismarkedwith
theletterC,installitwiththemarkontheside
towardtheidleportwhenviewedfromtheflange
endofthecarburetor.Tocentertheplate,backoff
thetopscrew,closethethrottleleverandthenset
theplatebytappingitwitha smallscrewdriver.
2. Installthechokeshaftandplate.Centertheplate
inthesamemannerasthethrottleplate(seestep
1). Usenewscrewsandlockwashers.
3.Installthefuelinletvalveseatandvalve.
4. Installthefloatandfloatpin,adjustingthefloat.as
previouslydescribed.
5.Installthebowlringgasket,bowlandbowlnut.
Makesurethatthebowliscenteredinthegasket
andtightenthemainjetassemblysecurely.Turn
inuntilitseatsandbackoutto1-1/2turns.
6.Installtheidleadjustingscrewfinger-tight.Then
backitout1 to1-1/2turns.
7.Installthechokeandadjustaspreviouslydescrib-
ed.
8.Installthecarburetorontheengineandconnect
thegasolineinlet,,governormechanism,air
cleanerhose,andchokewires.
9.Adjustthecarburetorneedlesettingsasdescrib-
edunderAdjustmentsandcheckouttheperfor-
mance.
CompleteReplacement:Completereplacementof
thecarburetorshouldbeperformedasfollows:
1. Followthepreviouslygivendisassemblyinstruc-
tionsasrequired-forremovalofthedefective
carburetor.
2. Replacethecarburetorvyitha newunit,using
-attachingpartsingoodconditionandmakingall
theconnectionspreviouslydisengaged.
3. Adjust the needle settings as described under
Adjustments.
17

DIAPHRAGM FUEL PUMP
Someenginesusea diaphragm-typefuelpump,
Figure16.Iffueldoesnotreachthecarburetor,check
thefuelpumpbeforedismantlingit.
1. Disconnectthefuellineatthecarburetor.
2. ' Crank'theengineandobservewhetherfuel
comesfromthelineatthecarburetor.
WARNING Besuretodirectthefuelflowintoa
containersogasolinedoesnotspillon
ignitionwires.
3.Ifthereisenoughfuelinthetank,andlinedoes
nothavefuelflowing,thepumpneedsreplacing.
Pumpfailureisusuallycausedbya leaking
diaphragm,valveorvalvegasket,a weakorbroken
springorwearinthedrivelinkage.Gasolinediluted
oilmayalsoindicatea faultypump.
Alwaysreturnthehandprimingleverallthewayinwardsothat
leverdoesnotpreventnormaloperationoffuelpump.
UPPERPUMPBODY
(NOTSERVICEABLE)
•VALVE0>
GASKET-0>|!
"LOWERSIDE
DIAPHRAGMGASKET"
LOWER
BODY
•PARTSINCLUDED
INREPAIRKIT
2. Makeanindicatingmarkwitha fileacrossa point
attheunionofthefuelpumpboltandcover.
Removetheassemblyscrewsandtheupper
pumpbody.
3.Turnthepumpbodyoverandremovethevalve
platescrewandwasher.Removethevalve
retainer,valves,valvesprings,andvalvegasket,
notingtheirposition.Discardthevalvesprings,
valvesandvalveretainergasket.
4. Cleanthepumpbodythoroughlywitha solvent
anda finewirebrush.
5.Holdingthepumpcoverwiththediaphragm
surfaceup,placethenewvalvegasketinthe
cavity.Assemblethevalvesinthecavity.
Reassemblevalveretainer.Lockinpositionby
insertingandtighteningthefuelpumpretainer
screw.
6.Placethepumpbodyassemblyina cleanwork
areaandrebuildthelowerdiaphragmsection.
7.Holdingthemountingbracket,pressdownonthe
diaphragmtocompressthespringunderit,then
turnthebracket90degreestounhookthe
diaphragmsoitcanberemoved.
8.Cleanthemountingbracketwitha solventanda
finewirebrush.
9.Replacethediaphragmoperatingspring,stand
thenewspringinthecasting,andpositionthe
diaphragm.Pressdownonthediaphragmto
compressthespringandturnit90degrees.This
willreconnectthediaphragm.
Holdthebracket,placethepumpcoveronit
(makingsuretheindicatingfilemarksareinline)
andinsertthefourattachingscrewsbutdonot
tighten. Withthehandonthemountingbracket
only,pushthepumplevertothelimitofitstravel
andholdinthispositionwhilethentighteningthe
fourscrews.Thisisimportanttoprevent
stretchingthediaphragm.
11. Mountthefuelpumpontheengine,usingnew
mountinggaskets.Connectthefuellines.
PULSATING DIAPHRAGM FUEL PUMP
Pulsatingdiaphragmfuelpumps(Figure17)usea
combinationofcrankcaseandspringpressureto
worka diaphragmthuspumping fuel. Thispumpmay
bemountedontheenginerearhousingonNHCV
modelsandontheupperrighthandcornerofthe
blowerhousingonNHCmodels.SeeFigure17.
10.
FIGURE16.DIAPHRAGMFUELPUMP
FuelPumpReconditioning:Reconditioningofthe
fuelpumpshouldbeasfollows,referringtoFigure16.
1. Removethefuellinesandmountingscrews
holdingthepumptotheengine.
Onthedownstrokeoftheenginepiston,whenthe
crankcasepressureisgreatest,thepumpdiaphragm
isforcedbackagainstthediaphragmspringcom-
pressingitanddrawingfuelintothepumpintake
chamber.Thefuelthenpassesthroughtheintake
reedvalveintotheoutputchambersideofthepump.
Onthecompressionstroke,whencrankcasepressure
isthelowest,thediaphragmspringforcesthe
18