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USAC.25GX120TechManual 1

HONDA120–TechManualUpdatedNovember2,2012

FROM2013USACNATIONAL.25MIDGETRULEBOOK,APPENDIXI731EngineProtestRules(appliestoHondaandBriggsclassesonly)

1. Protestshallbefromwithinthesamedivisionofclassonly,i.e.Jr.,Sr.,Lt.&Hvy.120‐

160,AnimalorWorldFormulaonly.Competitorsinthesamedivision,andinthesameracemaymakeaprotestonanengine.NoprotestinginRookieClass.Handlersmaynotprotestmorethanonecarpereventandmaynotprotestsamedrivermorethanoncepercalendaryear.

2. HondaEnginesandWorldFormula/AnimalEnginesmaybeprotestedfor$400.00cashonlyplusanyapplicableshippingchargesifnecessary.Noprotestedrelatedinspectionwillbestartedpriortothefundsbeingpostedwiththeproperofficial.

3. ThisprotestformandcashmustbesubmittedtotheChiefSteward,orhis/herdesignee,beforetheendoftheracethattheprotestedengineisparticipatinginI.E.Checkeredflaglapcomplete.

4. TheprotestcanonlybemadeduringanA‐Mainevent.5. Thepersonprotestingthemotormusthavetheirengineinspectedforcompliancefirst.

Ifthe“protester’s”engineisfoundillegaltheprotestisnullandvoidandtheprotestfeewillgototheclub.Ifthe“protester’s”engineisfoundlegaltheprotestwillcontinue.

6. TheChiefSteward,his/herdesignee,willholdtheprotestmoneyuntiltheprotestedenginehasbeeninspectedforlegality.Theprotestedengineshallbetagged/markedandsealedassoonasitcarcomesacrossthescaleifithasnotbeensealedprior.

7. Theprotestedengineaswellastheengineoftheprotestedpartyshallbeimmediatelytakentoimpoundand/orpresentedtotheTechDirectorforinspection.Enginemustremaininimpoundandinthepossessionoftechofficialsthroughouttheentireprocess,includingshippingtoUSACHeadquartersordesignatedtechinspectionstationandthetransferringoffunds.

8. Bothprotesterandprotesteehavetheoptiontobepresentatthetimeofinspection.9. Anyprotestthatiswithdrawnwillbeassesseda$50.00feethatwillbepaidtothehost

club.10. Iftheprotestedengineisfoundtobeillegal,themotormustbecompletelytorndown

tocheckforadditionalillegalities.TheTechDirectormustconfiscateallillegalpartsandrelatedpartsfromtheprotestedengineandshallimmediatelyforwardthemtotheUSACHeadquarters.Ifengineisfoundillegalprotestmoneyminus$50plusanyshippingcostwillbereturnedtothepersonfilingtheprotest.


11. Refusalofprotest,destroyingorwithholdingofpartsoranyotherlackofcooperationinthisprotestorinspectionprocessshallbeinterpretedasanadmissionthattheengineisillegalandshallsubjectthedriverandhandlertotheconditionssetforthintheSuspensionsProgram.

12. Anytechedorprotestedengine,blockorpartwhicharedeemedtobeovermaximumwearlimitsinoneormorespotsbutisundermaximumwearlimitsinotherspotsissubjecttoconfiscationbutnotDQ’able.

13. Note:ReferencetoConfiscationduetoWearLimitsin“EngineBlockInternalRules”ofbothManuals.

14. Iftheengineisfoundlegal$400willbegiventothepersonwhoseenginewasprotested.

732EngineSuspensionRulesHandlersanddriversguiltyofhavinganenginedeclaredillegalattechnicalinspectionsshallbedisciplinedasfollows:

1. Firstoffense–upto30‐daysand/or4racesuspensionforhandleranddriverfromparticipatingintherespectiveclassatanyUSACSanctionedevent.

2. Secondoffensewithinoneyearoffirstinfraction–One‐yearsuspensionforhandleranddriverfromparticipatingintherespectiveclassatanyUSACSanctionedevent.

3. Thirdoffensewithintwoyearsoflastinfraction–SuspendedforlifefromUSAC’s.25Midgetdivision.

4. SuspensionforlifeisopentoreviewbyUSAC.5. Suspensionshallbeginimmediately.6. IllegalHonda,AnimalandWorldFormulapart/sshallbesentwithinfiveBusinessdays

totheUSACofficeordesigneeforreview.TheTechdirectorhas48hourstodetermineifthepart/sarelegalorillegal.Ifthepart/saredeterminedtobelegalitshallbereturnedtohandler.Handlershallbenotifiedifpart/sarelegalorillegal.Allillegalorconfiscatedpart/sshallbesenttoNationalTechDirector.Alllegalpartsshallbereturnedtohandler.

7. IfaHondamotorisfoundtohaveavalveoilsealduringtechitshallbearacedisqualificationonly.

8. Sparkplugsandexhaustinfractionsarearacedisqualificationonly.9. Failuretogototechand/orimpoundwillresultinaracedayDQ.

Refusaloftechshallbeinterpretedasanadmissionthattheengineisillegalandasuspensionfromtheclassshallbeimmediatewithallawardsandqualificationsbeingrevokedwithasix‐monthsuspensiondriverandhandlersuspensionatanyUSACSanctionedevent.

10. Forthepurposeofthisruleonly,ifahandlerhasmultiplecarscompetingatoneraceeventandmorethanoneengineisfoundtobeillegalatthatevent;itwillbeconsideredtobeoneoffense.

11. AllmembershipsuspensionsmustbesenttotheNationalTechDirectorwithin5BusinessDays.


12. IllegalRookieenginepartsshallbeconfiscated(HondaorAnimal)butthesuspensionshallnotbeleviedagainsthandlersordriversforthefirstoffense.Thesecondoffenseshallresultina30daysSuspensionfromRookie.

13. Thecosttoappealasuspensionis$175plusanyassociatedfees.Theappealmustbemadewithin3daysoftheruling.

UNLESSITSAYSYOUCANDOITYOUCANNOTDOIT!!!GENERALRULES

1. “GX120UT2ENGINESWILLBEALLOWEDFORUSAC’S.252013SEASON.”2. OnlystockHondaGX120HX2Engineandgearboxwillbeusedinthisclass.Allpartswill

bestockHondaspecificallymadefortheHondaGX120K1HX2,U.S.GC01GCAHK,andCanadaGCAAT.HondaOEM120replacementblocksmaybeused.MustbeanOEMHondareplacementblock.Noaftermarketblocksorcomponents.

3. AllstockHondapartsmustbeusedandproperlyinstalledwiththefollowingexceptions:

a. Governorsystemmaybepartiallyorfullyremovedwiththeexceptionofthesteeldrivegearonthecrankshaft.Thisgearmustremainintact.Ifshaftisremovedholemustbeplugged.Holecanbetappedforthreadorepoxy.Nowelding.

b. Factoryaircleanermustberemoved.Anyairfiltermaybeattachedtotheoutsideofairfilteradapter.Outerwearstyleorequivalentcanbeusedovercarburetoronlywithnoadapter.Theapprovedairfilteradaptermayberunwithorwithoutanairfilter.Anyairfiltermaybeusedwithadapteraslongastherearenodevicesinsidetheairfilteroradapter.(I.E.Springsnotallowed)Hosefromvalvecovermustgointoacatchcan.(Weareusing“outerwear”todefineastylenotbrandname).

4. Theuseofairfiltersduringqualifyingatasphaltanddirteventsisillegal.TheSeniorTech.Officialreservestherighttoallowfiltersatanyeventthatit’sdeemednecessary.

5. Anytypeofthrottlelinkagemaybeutilized.Carburetorshallremainunalteredwiththeexceptionoftheblackplasticpieceontheupperendofthethrottleshaft.ThisistheONLYpartofthecarburetorthatmaybealtered,removedofmaterialfromtheblackplasticpieceisallowed.Noadditionalmaterialmaybeaddedtothecarburetor.i.e.boltinblackplasticpieceortubingonthrottlestop.

6. StockHondafueltankmustberemoved.7. Recoilstartermustberemoved.Pullcupmaybecutdownforwasher.Mustuseoriginal

cup.8. Exhaust:

a. StockHondamufflerwillberemoved.Mountingflangemaybecutoffofmufflerandusedasadapterflange.Anytransitionfromthe“D”shapeoftheexhaustporttoroundmusttakeplacewithinthethickness(0.250”max).oftheflange.Thisappliestoallexhaustsystems.Nostepsortapersallowed,gridmarksareallowedpast.25”flangearea.Nosuspensionforexhaustflangeorpipe


infractionjustdisqualification.Ifanaftermarketflangeisused,maximumallowableflangethicknesswillbe0.250”.Ifslipontypeflangeassemblyisused,pipestubwillbeamaximum0.880“outsidediametertubingwithamaximumoveralllengthof1.500”.Pipestubmustbeinsertedintoexhaustpipeatleast0.750”andwillhaveminimalexhaustleakage.

b. AllUSAC.25midgetmufflerstobeusedwillbe4to8hpBriggs&Stratton,partnumber294599orequalequivalent.Mufflerwillbeinternallyunalteredexceptthattheroundcupshapedbafflemaybeweldedtotheperforatedbafflewithoutmovingit’soriginallocation.Nodrillingholesinthebaffles.Insideseamofbafflemustbestraightedged.(NOTE:Someseamsmaynotbestraight).Threadswillnotberemovedfromthemuffler.Itisoktoweldawasherornutontheflangeforaplacetoapplysafetywireand/orspring.

c. Exhaustpipewillbeamaximumof1.000”outsidediameterwithalengthof20.0”to26.0”includingathreadedpipecouplerweldedtotheendofthepipeinordertoscrewmufflerinplacesothatmufflermayberemovedforinspection.Pipecouplerwillbeastandard,unaltered,¾”NP,threadedcoupler.Lengthwillbe1.000”minimumto2.250”maximum.Exhaustpipelengthwillbemeasuredbyusingasmalldiameterhoseinsertedthoughpipetomeasureoveralllength.Flangeandcouplerwillbeincludedintheoveralllengthwhenmeasuringpipe.Nocoatingofanytypemaybeappliedtotheinteriorofanypartoftheexhaustsystem.Theintentofthisruleistohavealloftheexhaustpassthroughthemuffler.Allmeasurementsaretobetakenwiththecomponentpiecesinthesamepositionastheywereinstalledandonthecar.

9. Chokebutterflyandshaftmustberemoved.Onlythetopholemaybefilledonlywithsiliconeoroldshaftcutdown.Noadditionorsubtractionofmaterialintheboreorventuriofthecarburetor.

10. Oillevelswitchmaybedisconnectedbutswitchassemblymustremainintactincrankcase.

11. Gearboxmayberotatedtoanydesiredposition.12. MainJetincarburetorwillbe“NONTech”.MustbeaOEMHondaJet(brassorsilver

jet).Jetcanbedrilledtoanysize.Nomodificationstothejetexceptfordrillingthemainhole.

13. On‐Offignitionswitchmayberemoved,andholecovered.(anymaterial:nowelding)14. Allpinmeasuringgaugesareplustolerance.15. ExhaustoxygensensorortemperaturesensorattachedtoanypartofHondaexhaust

systemisillegal.16. Valvesealsareillegal.17. CryogenicsofanyHondapartisillegal.18. Takingpartsoutofservice‐Reference:WearlimitsinEngineBlockInternalsection.19. DQonly–Notsuspensionfor:Exhaust,AirFilterAdapter,SparkPlug20. ShroudmaybefactoryREDorBLACK.21. Hondagasketsfortheintake,carb,sidecoverthataregreenononesideandtanonthe

otherincolorarelegal.


TECHPROCEDUREModificationsormachiningofanypartsexceptthegasketsurfacesbetweenthecylinderheadandblock,andmainjetinordertobringthemtostatedminimumormaximumspecs(blueprinting)isnotlegal.

1. Externalvisualcheckofengineforrequiredcomponents:Pipeandmuffler,shroudsandsheetmetal,andoillevelsensor(thiscanbepartiallyobservedfromoutside).

2. Factoryaircleanermustberemoved.Anyairfiltermaybeattachedtotheoutsideofairfilteradapter.Outerwearstyleorequivalentcanbeusedovercarburetoronlywithnoadapter.Theapprovedairfilteradaptermayberunwithorwithoutanairfilter.Anyairfiltermaybeusedwithadapteraslongastherearenodevice(s)usedinsidetheairfilteroradapter.(I.E.Springsnotallowed)hosefromvalvecovermustgointoacatchcan.(Weareusing“outerwear”todefineastylenotbrandname).

3. Theuseofairfiltersduringqualifyingatasphaltanddirteventsisillegal.TheSeniorTech.Officialreservestherighttoallowfiltersatanyeventthatit’sdeemednecessary.

4. AnyTypethrottlelinkagemaybeutilized.Carburetorwillbeunalteredwiththeexceptionoftheblackplasticpieceonupperendofthrottleshaft,thisistheonlypartinthecarburetorthatcanbealtered,Mainjetis“NonTech”.Removalofmaterialfromtheblackplasticpieceisallowed.Noadditionalmaterialmaybeaddedtoanypartofthecarburetor,i.e.boltinblackplasticpiece,tubingonthrottlestop.

5. RearmountingbracketsforHondafueltankmayberemoved.6. Thestartercupthatisbehindtheflywheelretainingnutcanbecutawaytoleaveonly

theflatwasherbackpiecethatretainscoolingfan.7. Theykeyedendoftheringgearshaftmaybeshortened,drilledandtappedormachined

forsnapring.8. Heli‐coilingthreadsforshrouds(all),valvecover,existingthrottlemountingholes,oil

drain,andfillholes,oneofthecoilbolts,andsidecoverboltsisallowed.Dowelholesarenottobemodifiedorrelocated,alsoonecarburetormountingbolt.

9. Honinganddeglazingoftheboreisallowed.10. Lappingthevalvesisallowed.11. Blockingairflow:Nodevicemaybeusedthatwill/orappearthatitmayimpedeairflow

intotheenginecoolingsystem.Thismayrequirethattheengineberunataspeedaboveidlebythetechpersonnelatthescaleafterthecarhasqualifiedorraced.


CARBURETOR

HONDA120INSULATOR

HONDAGX120CARBURETORFORJUNIOR&SENIORHONDA


RemoveCarburetor:

Aircleaneradapter: ID: 2.250”maximum Length: 1.375”maximum Flangethickness: 0.375”maximum FlangeID: 1.000”minimum

IDholesizestraightwalled,flatbottomedandparallelwithcarburetorusingexistingaircleanermountholes.

1. Checkforrestrictor,ifapplicable,andplacement.RestrictormustbeinstalledbetweencarburetorandcarburetorinsulatorwithstockHondagasketoneachsideofrestrictor.OnlystockHondainsulatorgasketbetweenblackplasticinsulatorandheadispermitted.Airpassagewayininsulatorwillnotbealteredinanyway.AllJuniorHonda’smustusetheblueUSACapprovedslottedplateonly.Failuretouseproperrestrictorplate,alterationofrestrictorplate,orimproperinstallationofplateindesignatedclassiscauseforimmediateDQandallapplicablesuspensionswillbeapplied.

2. Gasketthickness:0.025”maximum.


3. Restrictorthickness:0.0625”maximum.NoslottingofholesonanyHondarestrictor.4. Insulatorgasketthickness:0.025”maximum5. Checkforanyalterationsorwornpartsthatwouldallowadditionalairintoengine:

holes,slots,perforations,spacers,loosebolts,warpedflanges,etc.6. TwostockHondaintakegasketsmaybeusedbetweenCarburetorandplasticinsulator.7. Carburetoridentificationnumber:

a. Jr.HondaandSr.Honda: BE60B,ThailandBE60R,UT2carbBE99Ab. HeavyHonda:BE65BorThailand65Q

8. Checkcarburetorforalterations.Upperchokeshaftholemaybesealedwithsiliconetypesealer.

9. Honda120carbforJr.andSr.Hondaa. BE60B,ThailandBE60R,UT2carbBE99Ab. CarburetorBore:Intakeend:Maximumdiameter0.950”c. Throttleend:Maximumdiameter0.632”.d. Carburetorventurebore0.456”nogo.Thismeasurementisbestmadewithano

gogaugebutmaybemadeusingatelescopinggaugeasanogo.e. Mainjetincarburetorwillbe“NonTech”.MustbeaHondaOEMjet.(Brassor

SilverJet)Jetmaybedrilledtoanysize.Noothermodifications.f. Mainairjet:0.0394”maximum#60(0.040”)nogo–atbackofholeg. Mainjetaccesspassage:0.094”maximum#41(0.096”)nogoh. Mainnozzlebore0.069”maximum#50(0.070”)nogo.i. MainnozzlewillbecheckedwithaNOGOgauge(.429”)Ifgaugegoesoverdump

tube‐carbisillegal.Thisisbestmeasuredusinga0.452”rodtypegaugewitha0.429”flatareatobeusedasagogauge.

j. Airventholesonthesideofthemainnozzlemustnotbeplugged.k. Mainnozzlemustnotbefastenedintothecarburetorbodybyanythingother

thanthemainjet.Itmustnotbeepoxiedorpositionedbyanyothermeans.l. Pilotjet: 0.0138”maximum#79(0.0145”)nogom. Pilotairjet: 0.050”minimum1.25mm(0.0492”)go.n. Pilotscrew:nospeco. Pilotseatdiameter: 0.035”maximum#63(0.038”)nogop. Tipofpilotscrew: 0.019”minimum.q. Floatbowlvent:0.118”maximum#31(0.120”)nogo.r. Needlevalveseat:0.065”maximum#51(0.067”)nogo.s. Thebutterflyscrew,thebutterfly,andthethrottleshaftmustnotberemoved

fromthecarburetor.Anyevidenceoftamperingwillbeadisqualificationandsuspension.

10. Honda160carbforHeavyHonda


MUSTUSEHondapartnumber16211‐ZE0‐000InsulatorfortheHeavyHondaclass.ThisisthestandardGX‐120Insulator.Nomodificationsallowed.

a. BE65BorThailand65Qb. CarburetorBore:Intakeend:Maximumdiameter0.951”ref.c. Throttleend:maximumdiameter0.710.d. Carburetorventurebore;0523‐no/go.Thismeasurementisbestmadewithano

gogaugebutmaybemadeusingatelescopinggaugeasanogo.


e. Mainjetis“nontech”MustbeanOEMHondajet(BrassorSilver)Jetscanbedrilledtoanysize.

f. Mainairjet:0.0587”maximum#53(0.095”)nogo‐atbackofhole.g. Mainjetaccesspassage:0.0942”maximum#41(0.096”)nogo.h. Mainnozzlebore:0.0732”maximum#47(0.078”)nogo.i. Mainnozzlewillbecheckedwithano/gogauge(0.424”)ifgaugegoesover

dumptube–carbisillegal.Thisisbestmeasuredusinga0.452”rodtypegaugewitha0.424”flatareatobeusedasagogauge.

j. Airventholesonthesideofthemainnozzlemustnotbeplugged.k. Mainnozzlemustnotbefastenedintothecarburetorbodybyanythingother

thanthemainjet.Itmustnotbeepoxiedorpositionedbyanyothermeans.l. Pilotjet: 0.0135”maximum#79(0.0145”)nogo.m. Pilotairjet: 0.0478”maximum#55(0.052”)nogon. Pilotscrew:nospeco. Pilotseatdiameter: 0.0365”maximum#63(0.037”)nogo.p. Tipofpilotscrew: 0.020”minimumq. FloatbowlVent: 0.118”maximum#31(0.1200”)nogo.r. Needlevalveseat: 0.0685”maximum#31(0.1200”)nogo.s. Thebutterflyscrew,thebutterfly,andthethrottleshaftmustnotberemoved

fromthecarburetor.Anyevidenceoftamperingwillbeadisqualificationandsuspension.

ENGINECOOLINGSHROUDS

1. Allpiecesofthestockenginecoolingshroudmustbeproperlyinstalled.2. Theremustbenoadditionorsubtractionofanymaterialfromtheshroudingexceptfor

thecoveringoftheswitchhole(anymaterial).Startercupmaybealteredtobeusedaswasherretainerforthecoolingfan.

3. Removeenginecoolingshrouds.Removevalvecover.4. Zerodialindicatorafterexhaustbump.(0.050)ref.5. Maximumvalveliftwillbecheckedfromthetopofvalvespringretainer.Valvesmaybe

adjustedtozeroclearanceorshimsmaybeinstalledtocreatezeroclearance.Thismaydictatemakingspecialshims,asitisdifficulttoinsertfeelergaugebladessoasnottointerferewithindicatorcontactsonretainer.Valvelift: Intake: 0.245”maximum

Exhaust: 0.255”maximumCYLINDERHEAD,HEADGASKET,VALVES,SPRINGS.

1. Removecylinderhead.2. Headgasketthickness:

0.040”minimumthicknessofinnerrim.3. Thicknessoftheheadwillbemeasuredfromvalvecoversurfacetoheadgasketsurface

ontheside,atapositioninlinewiththeupperintakeandexhaustflangebold.Noanglemillingofsurface.Minimum2.911.


MINIMUM2.911

4. Removevalves:5. Inspectretainersforalterationthatwouldincreasevalvespringpressure.Bothintake

andexhaustmusthavestockHondaretainers.Exhaustvalveonlycanhavelashcapandcorrespondingretainer.

6. Thicknessofretainerwillbe:Intake: 0.228”minimumExhaust 0.241”minimum

7. Flangethicknessofretainerwillbe:Intake: 0.110”maximumExhaust: 0.070”minimum

8. Fromflatofflangetomachinedsurface:Intake: 0.148”minimumExhaust: 0.165”minimum

9. Allvalveoilsealsmustberemoved.10. TheuseofvalvesealsisillegalandwillresultinapplicablesuspensionperHonda

suspensionprogram.VALVESPRINGS

1. ValvespringswillbestockHondaspringsandwillnotbealteredinanyway.UseofHondaGX120or140valvespringslegal

2. 120springs


a. Wirediameter: 0.071”maximumb. Outsidediameterofspring: 0.790”maximumc. Numberoftotalcoils: 5.3d. Springpressure: 11lbsmaximumat0.812”e. Stackedlengthwillbe: 0.394”maximum

3. 140Springs

a. WireDiameter: 0.079”maximumb. Outsidediameterofsprings 0.808”maximumc. Totalnumberofcoils:7d. Springpressure: 16lbs.maximumat0.812”e. Stackedlength0.524”maximum

ROCKERARMS–PUSHRODS‐STUDS

1. RockerarmswillbestockHondaandwillnotbealteredinanyway.2. RockerarmstudswillbestockHonda.Theyortheirmountingpositionmaynotbe

alteredinanymanner.Noheli‐coilingofmountingholes.Nobendingofstuds.3. PushrodswillbestockHondaandwillnotbealteredinanyway.

Pushrodlength:4.799”–4.770”

VALVES


INTAKEVALVE EXHAUSTVALVE1. Checkvalvesfordimensionsandweight.2. Valveseatingsurfacemustbefactorygroundtoasingleangleonly,45degrees.Therewill

benootheranglesgroundonanypartofvalve.Valvesmustnotbepolished,lightenedoralteredinanyway.

3. Valveweight:Intake18gramsminimumExhaust16gramsminimum

4. Drawingofvalvedimensions(intakevalvefollowedbyexhaustvalve)


Therearetwodifferentexhaustvalvecombinationsavailabletouse.Youcannotmixandmatchpartsfromthetwocombinations.

IfyouchoosetoruntheUT‐1exhaustvalvepart#14721‐ZF0‐000youmustuseRetainer#14773‐ZE1‐000andLashCap#14781‐ZE1‐000.

IfyouchoosetoruntheUT‐2exhaustvalvepart#14721‐Z4H‐000youmustrunretainer#14771‐ZE1‐000.YoucannotrunaLashCapwiththiscombination.TheUT2exhaustvalvepart#14721‐Z4H‐000measures~2.470overalllength.

HEAD

1. Cylinderheadwillbein“ascast”andinfactorymachinedcondition.Theremaybenoadditionorsubtractionofmetalexceptforcylinderheadgasketsurface.

2. Nouseofanysubstancetotheinsideofthecylinderhead.Thisincludesnotypeofmachiningorgrindingtoincreaseairflow.Noanglemilling,etc.oranyalterationthatcouldincreasevalvespringpressure.

3. Japan,UT1,andUT2headsarealllegal,butsomeoftheoriginalUT1headshadgrindingandfilingmarkslocatedintheports.HeadswithgrindingorfilingwillNOTbelegal.Itisyourresponsibilitytomakesureyourmotorsheadhasn’tbeengrindedorfiled.HPDhasJapan#13cylinderheadsavailable.

4. Thicknessoftheheadwillbemeasuredfromvalvecoversurfacetoheadgasketsurfaceontheside,atapositioninlinewiththeupperintakeandexhaustflangebolt.Noanglemillingofsurface.Minimum2.911.

5. Cleaningofthecombustionchamberorchangingthefinishofsuchchamberisillegal.

INTAKEANDEXHAUSTPORTS1. Portswillbein“ascast”andfactorymachinedconditionandtheremustbenoaddition

orsubtractionofmetaloranyothersubstancetotheinsideoroutsideofthecylinderhead.

2. Noalterationsofanykindtobemadetotheintakeorexhaustport.a. Thisincludesanygrinding,polishing,etching,sandblastingorglassbeadingto

interiorsurface.3. Valveseatsmustbeastocksingle45degreeangle.Multianglevalveseatsarenot

permitted.Valveseatsmustnotbereplaced.4. IntakeandExhaustportsatvalve:

Intake: Maximum0.752”Minimum0.745”

Exhaust: Maximum0.675”Minimum0.665”


ENGINEBLOCK

MustbeanOEMHondaCylinderblock.Noaftermarketblocks.

1. Thisengineblockmustbein“ascast”andfactorymachinedcondition.Theremustbenoadditionorsubtractionofmetaloranyothersubstancetotheinsideoroutsideofthecylinderblock,crankcasecover,crankshaft,rod,piston,pin,rings,flywheelorcoilwiththefollowingexceptions:

a. Removalofreargastanksbracketsispermitted.b. Removalofgovernor.Governorsystemmaybepartiallyremovedwiththe

exceptionofthesteelgearonthecrankshaft.Thisgearmustremainintact.Governorarmandshaftmayberemoved,tiedforwardoralteredtoaccommodatethrottlelinkageorreturnsprings.

2. Additionofbrackets,fittingsetc.toaccommodatethrottlelinkage,tachometerandtemperaturegaugeisallowed.

3. Cylinderheadgasketsurfacemaybemilled,butmustbeflat.Noanglemillingallowed.4. Checkbore:

2.366”maximum.NOTE:Allmeasurementstakenattopofboreorverybottomofbore,preferredmethodofmeasurementisdialboregauge,dialcalipersmaybeused.


“WearLimits/PartsOutofService”USACreservestherighttoconfiscate120HondaenginepartsdeemedillegaloratUSACmaximumwearlimits.EXAMPLE:cylinderborewillbe2.366maximumallmeasurementstakenattopofboreorverybottomofboreparalleltocrank,90degreesfromcrank.AnycylinderblockthathasonemeasurementoverUSACmaximumwearlimitswillbetakenoutofservice.IfnomeasurementsexceedUSACmaximumwearlimitsthepartoftheblockwillnotbeconfiscated.Handlerhastherighttohaveconfiscatedpartsreturnedtothembutwillberenderedunusable.

5. Checkstroke:1.659”Maximum1.640”Minimum

6. MeasureamountthatpistonisupordownfromblocksurfaceatT.D.C.Thiswillbemeasuredattheedgeofpistontopandbottomandsidetoside.Whenmeasuringtopandbottomofpistontakeanaverageofthenumbersmeasuredi.e.top=.003,bottom=‐.003thepistontodeckwouldbe.000.MeasurementmustNOTbetakeninthecenterorrelievedpartofthepiston.Thisdimensionwillbe:0.000”Max–NOPISTONPOPUP!!!Carbonmayberemovedtocheckpop‐up.

7. Installdegreewheelonflywheel.Installpointerinordertoreaddegrees.LocateaccurateT.D.C.thisshouldbedonewithapositivestoptypefixtureandnotestablishedwithindicatoralone.

8. Camwillbecheckedwithindicatorreadingoffthetopendoftappetswhichwillprovidezeroclearance.Theinvertedradiusofthetopofthetappetpresentssomeproblemtogetaccuratereadingsandtopreventbindingofindicatorstem.Indicatorholderandpositionsareverycriticalinthisoperation.

9. Zeroindicatoronbasecircleofcam.Besurethatcompressiondoesnotaffectzeroingexhaustindicator.(zerodialindicatorafterexhaustbump)ref.

10. Turningengineinnormalrotation,clockwisefacingflywheel,takereadingatspecifiedopening.Readingsmustfallbetweenspecifieddegreesonthefollowingchart.

CAMSHAFTPROFILELIMITS

INTAKE EXHAUSTDegrees Degrees


0.050”10.5to14ATDC 0.050”207to210.5BTDC0.100”26.5to30ATDC 0.100”190to193.5BTDC0.150”45to48.5ATDC 0.150”170.5to174.5BTDC0.180Split 0.180Split0.200”71to74.5ATDC 0.200”144to148BTDCMaxlift.227Peak104–107ATDC Maxlift.229”Peak107.5‐110.5”BTDC0.200”136to141ATDC 0.200”70.5to73.5BTDC0.180split 0.180split0.150”162.5to167ATDC 0.150”44.5to47.5BTDC0.100”180.5to185ATDC 0.100”26to29.5BTDC0.050”197.5to201ATDC 0.050”9to12.5BTDC

11. Checkmaxliftatintakeandexhaust.FLYWHEEL,FANANDIGNITIONSYSTEM

TierIIIFlywheel TierIIFlywheelBlackMagnetmustbestraightupTimingKey. WhitemagnetmustuseoffsetTimingkey.

Cautionshouldbeusedwhenremovingflywheel.Donothitwithhammerorotherheavyobjects.Servicemanualshowflywheeltoberemovedwithcommerciallyavailable6”puller.Anothermethodisinertiatypeknockerthatthreadsontocrankshaftend.

1. Thetransistorizedmagnetoignitionisfixedat20degreesBTDCandmaynotbealteredinanyway.

a. Firingmustnotexceed66.5”or20degreesBTDC.Quickcheck:Turningflywheelclockwiseiftheleadingedgeofdepressionofflywheelrimwherethemagnetismountedisnotstillundertherighthandcoillegat.065”BTDC,itisprobablyillegalandshouldbecheckedfurther.

PROCEDUREFORCHECKINGTIMINGA. Withdegreewheelorindicatorlocatedat0degreesorTDC.,markboththe

flywheelandsomefixedpoint(suchasrighthandsideofaluminumblockcasting


rightaboveflywheel)withaligningmarks.Turntheflywheelclockwiseandstopat20degreesBTDCor.0655”–0.0665”BTDConyourindicator.Makeanothermarkontheblockcastingthatalignswithyourmarkontheflywheel.

B. Removedialindicatorsoitwillnotbedamagedbyenginerotation.C. Installtiminglighttoabattery,ifnotselfpowered,andclampinductivepickup

tosparkplugwire.Wireshouldbehookedtostandardsparkpluggappedto0.025”.Usingadrill,withanextensionthatiscutofforturnedtofitdrill,placesocketonflywheelnutandrotateengineinclockwisedirection.

D. Firethetiminglightandobserve.IfthereferencemarkontheflywheelisbetweenthetwomarksonblockcastingthatareTDCand66.5”or20degreesBTDC,thetimingislegal.Ifmarkisnotbetweenmarksonblockcastingwhenrotating,theenginewillbedisqualified.

2. Flywheelkeywayoritspositionmustnotbealtered.3. Keymaynotbedeletedoralteredinanyway.YoumustrunaUSACapprovedkeyfor

timingonoldstyleengineswithoutTierIIIflywheel.4. Magnetand/oritspositionmaynotbealteredinanyway.TierIIImagnetblack,oldstyle

magnetwhite.5. Magnetretainingscrewmaynotbealteredinanyway.Screwmaynotbereplacedwith

largerorsmallerscrew.Noheli‐coilingofmountinghole.6. Ignitioncoiland/oritsposition,otherthanairgap,maynotbealteredinanyway.

a. Coilmountingboltsmustbestockandcannotbealteredinanywaytoadvanceorretardtiming.Coilattachingboltswillbestock6mmcapscrew1‐1/16”long.

b. Therecanbenomorethan3/8”ofunthreadedportionofboltthatdoesnotmeasure0.230”diameter.Thisrestrictsmovementofcoiltoapositionthatcouldmakeignitiontimingillegal.

c. Ifacoilsupportmountbecomesstripped,itispermissibletoheli‐coil.However,onlyonelegmayberepaired,ifbothlegsareheli‐coiled,theblockbecomesillegal.

7. Allnylonbladesonthecoolingfan.8. Nometalremovaloradditiontoflywheelispermitted.9. Flywheelweightwillbe:

1550gramsminimum10. Flywheeldiameter–magnetarea:

6.285”minimum11. AstockHondasparkplugcap,(wireendatresistor),mustbeused.12. Anyautomotivetypesparkplugwith¾”reachmaximumisallowed.13. Noplugindexingwashersallowed.14. Iftemperaturesensorisusedundersparkplug,factorywashermayberemoved.


GX‐120FANGEARBOXANDRINGGEAR

1. Gearboxmaynotbealteredinanyway.a. Mayberotatedtodesiredposition.

2. Ringgearmaynotbealteredinanywaywiththeexceptionofthekeyedendofshaftthatmaybeshortened,drilledandtappedormachinedforsnapringgrove.Noothermachining,drilling,grindingetc.toringgear.

a. Keywaymaybecutdeeper.3. Ringgearmaynotbealteredinanywayincludingpolishingoruseofanycompoundor

abrasiveongearshaftwherebearingrides.4. Twogasketsmaximumbetweengearboxhalves.

CRANKCASECOVER

1. Removecrankcasecover.2. Covermustbein“ascast”andfactorymachinedconditionandtheremustbeno

additionorsubtractionofmetaloranyothersubstancetocrankcasecover.3. CrankcasecovergasketmustbestockHonda.Onlyonegasketmaybeinstalledwitha

maximumthicknessof0.025”.4. Criticaldimensionsarethrustfaceofcamshaftholderandpositionofcrankbearing.


a. Placeastraightedgeovercrankbearingandcambossthrustface.Thesesurfacesshouldbelevel.

b. Maximumtolerancewillbe0.005”.Therewillbenoalterationstocrankcasecover.Thisincludesanyalterationtocrankbearingandcamshaftholderpositionandheightinanattempttoaltervalvetiming.

PISTON,WRISTPIN,ANDPISTONRINGS

1. Removerodandpiston–triangleorbossontopofpistonmustpointtowardpushrods2. Piston,wristpinandringsmustbeabsolutelystockandnotalteredinanymanner.

TIERIIIPISTON TIERIIPISTONPISTON1. PistonwillbestockHondastandardsizeandwillnotbealteredinanyway.2. Oversizedpistonsmustnotbeused.3. Allthreepistonringsmustbeused

a. Topring:Chromecompressionringinstalledwith“N”or“T”onarailup.Noexpanderunderring.

b. Middlering:Oilscraperringinstalledwith“N”or“T”onrailup.Noexpanderunderring.

c. Bottomring:Three(3)pieceoilringsareallowed.4. Pistonmaynotbeknurled,groovedorcoated.5. Pistonweight:

106gramsminimum.6. TotalPistonweightwithrings,pin,andclips:

121gramsminimum.7. TotalPistonweightwithrings,pin,clips,completewithrodandbolts:

263gramsminimum.8. Seedrawingfordimensions.


RINGS1. MustbestockHondaringswithstocksizeandconfiguration.2. Nodecreasingofringtensionbyheating,machiningoranyothermeans.3. TierIIPistonRingThickness:

a. Compression:0.056”min.b. Scraper:0.056”min.c. Oilring:3piecelower0.095”min.

i. 1piece0.097”min.4. TIERIIIRingThickness:

a. Compression:0.036”min.b. Scraper:0.036”min.c. OilRing:3piecelower0.095”min.

i. 1piece0.097”min.5. Theletter“N”or“T”onTierIIIpistonringsmaynotbelegibleafterenginehasbeen

run.WRISTPIN

1. StockHondawristpinandretainera. OD:0.511ref.b. Length: Minimum1.844”

Maximum1.864”c. ID:0.354”ref.d. Weight: 23gramsminimum

CONNECTINGROD

1. StockHondarodwithnoalterations.2. Connectingrodbigendsize:

1.021”minimum1.0265”maximum

3. Pinendboreis0.5111ref.4. Lengthfrombottomofpinboretotopofbigendborewillbe:


2.111”maximum2.101”minimum

5. Rodweightwithbolts:119gramsor4.2ozminimum6. Nooilgroovesonbearingsurfaceofeitherend.

CRANKSHAFT

THAILANDCRANKSHAFT JAPANCRANKSHAFT

1. StockHondacrankshaftwithnoalterations.2. Noremovaloradditionofanymetalfromortothecrankshaftisallowed.3. Nobalancingofthecrankisallowed4. Nooilgroovingisallowedonthecrankjournal5. Governordrivegearcanotberemoved.6. Crankshaftdrivegearshouldnotberemoved.ThisgearisinstalledbyHondatoany

accuracyof+½degree.Ifthisgearisnotinstalledtothisdegreeofaccuracy;enginemaynotbelegalwhencamshaftischeckedbytheprocedureunderengineblock.

7. Keywaylocationmustnotbealteredinanymanner.8. Measurethrusttocrankgearside:3.345Min.9. Theonlycleaningmethodallowedisontheflywheelsideofcrankshaftforthepurpose

ofremovingcalcium,rustetc.fromtheexposedendofthecrankshaft.Thisispermittedonlyfromthesealgrooveouttotheendofthethreadofthecrankshaftwheretheflywheelboltson.Onlyawirewheelmaybeusedinthecleaningprocess.TheuseofScotchbrite,sandpaperoranyothercompoundsorabrasivesisillegal.Nomaterialmaybeaddedorremovedfromcrankshaft.

10. Crankshaftmainjournalatflywheelandgearboxendsmaynotbealteredinanyway.


CAMSHAFT

1. CamshaftmustbestockHondawithnoalterationofanykind.2. Therewillbenoadditionstoorsubtractionsfromanypartofthecamshaft.

3. Compressionreleasewillremainintactandunaltered.4. Lobecenteranglewillnotbealteredbyanymeans.5. Lobeprofilewillnotbealteredinanyway.6. Camshaftspecifications

INTAKE EXHAUSTHeeltoheel0.864”–0.869” Heeltoheel0.865”–0.870”HeeltoPeak1.079”–1.093” Heeltopeak1.081–1.095”

Length–thrustflangetothrustflange:3.137”minimum3.142”maximum

7. Cambearingsare0.547”–0.551”andunaltered.TAPPETS

1. TappetsmustbestockHondawithnoalterations.2. Basediameter:

0.909”minimumNomaximumspec.


3. Stemdiameter:0.312”minimum

4. Basethickness:0.076”minimum0.090”maximum

5. Length:1.181”minimum1.220”maximum

6. Weight:16gramsminimum

ENGINEBLOCKINTERNAL

1. Theengineblockmustbeinan“ascast”andfactorymachinedconditionandtheremustbenoadditionorsubtractionofmetaloranyothersubstancetotheinsideoroutsideoftheblockexceptforcylinderheadgasketsurfacemaybemilledtoachievea0.00pistonpopup.Noanglemillingofthecylindersurface.Mustremainflat.

2. Cylinderborewillbe2.366”maximum.NOTE:allmeasurementstakenattopofboreorverybottomofbore.

“WearLimits/PartsOutofService”USACreservestherighttoconfiscate120HondaenginepartsdeemedillegaloratUSACmaximumwearlimits.EXAMPLE:Cylinderborewillbe2.366Max.allmeasurementstakenattopofboreorverybottomofboreparalleltocrank,90degreesfromcrank.AnycylinderblockthathasonemeasurementoverUSACmaximumwearlimitswillbetakenoutofservice.IfnomeasurementsexceedUSACmaximumwearlimitsthepartofblockwillnotbeconfiscated.Handlerhastherighttohaveconfiscatedpartsreturnedtothembutwillberenderedunusable.

3. Cylinderborewillnotbeboredoversize.4. Cylinderborewillnotbere‐sleeved.5. Cylinderborepositionwillnotbemovedortippedinanymanner.6. Therewillbenopolishing,sandblastingorglassbeadingtoanyinteriorsurface.7. Machinedsurfaceofblockdowntothrustfaceofcamboss:

3.228”minimum3.240”maximum

8. Machinedsurfaceofblockdowntobearingface:3.430”minimum3.442”maximum

9. Oillevelsensorwillbeintactandunaltered.Wiresmaybeexternallydisconnectedorcutoff.


Techofficialshavetherighttotechanyorallcarsinanyclassattheirdiscretion.

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