Onan MJA Series Service Manual Download Page 1

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Summary of Contents for MJA Series

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Page 3: ...anual primarily for reference when servicing MJA MJB and MJe generat ing plants Tbis is what it was designed for But inaddi tion ONAN recommends that you study the whole manual It will help to acquain...

Page 4: ...6 Specification Number Denotes Customer Requested Deviations from Standard Model 1 Specifica tif fl Letter Advances with ONANchanges 5M JB Some models have generators reconnectib1e for either code 1 2...

Page 5: ...Cylinder Heads and Valves 3 8 Pistons Connecting Rods Cylinders 3 9 Engine Disassembly 4 GENERATOR REVOLVING FIELD 705MJB MJC 5 GENERATOR REVOLVING FIELD 3MJA 4MJA and 5MJB 6 CONTROL SYSTEM 7 ASSEMBL...

Page 6: ...3 7 3 3 4 3 3 3 6 2 3 2 6 3 3 4 5 3 2 7 3 9 3 3 4 3 9 3 SUBJECT Flyball Spacer see camshaft gear Fly vheel Fuel Fuel Pump Fuel Strainer Gasoline Carburetor Gear Cover Generator Blower Generator Brush...

Page 7: ...enerator Air Baffle Battery Charging Winding Brushes Bearing EXCiter Rotor Collector Rings SECTION 3 8 5 3 5 6 3 5 1 3 5 4 3 5 5 3 5 2 3 5 3 9 5 5 3 9 2 2 3 9 2 3 7 5 3 5 2 3 8 3 3 8 4 3 B 6 3 B 5 7 2...

Page 8: ...II1I IaI is I I E III II IaI II III IaI IaI 0 l 1 l 5 z i m TI e II u r 0 0 l m il z 1 e U I TI TI 00 r II l 0 r or 1 r em e II m e e l en u r il l en m lz _I r u r I 0 zm mm 1 ilm u r m e r l 1 J IO...

Page 9: ...I I __ J 1 t g t J r I i t Ii W II I j 7 u r l__ I t 1 ale 1 111 I tl p I J iF tU I 0 J e 6 u l I l c I I I E __ 1 I I i icJ I N l _ JI I f I I l M t j J t I I SPARI PLUGS START DISCONNECT SWITCH AND...

Page 10: ...0 il 0 re rn 0 rnfJ r 0 i i m 0 r Q r OJ l fJ 0 rn 0 tJ tJ Q 1ft 1ft nI nI Ill 1ft Q z i I I I AI 61ft 1ft 6 0 i fJ l i i fJ i i I Ir AI 0 0 e fJ r e i rn Zrn 11 r r e m i 11 6J1e 7 l 1 r cO e fJ i f...

Page 11: ...Check Fuel Supply x 3 2 1 Check Oil Level x 3 5 1 Clean Governor Linkilge I it 3 4 1 Service Air Cleaner Silencer xt 3 2 6 Change Crankcase Oil x 3 5 1 Clean Crankcase Breather x 3 5 7 C ean and Adiu...

Page 12: ...2 v 12 v 12 v two in sertes two in two in two in series 105 series series 165 105 105 5 MJBGONTROLWffirnG DlAGRAM low oHpressure ctrcmt E It i 3 I r 1 z sX r I I __ 1 Il Priorto SpecF Models e z r t 9...

Page 13: ...discharged See Trouble Shooting Chart 7 Control circuit defective See Sect 6 Internal seizure Disassemble engine and repair Engine oil too heavy for See Sect 3 5 1 for oil operation in low temper reco...

Page 14: ...e 1 1 1 LDZ Ul o ttl IO C j t Z 0 _ Defective fuel pump Ignition system faulty See Trouble Shooting Chart 4 Carburetor choked too Check choke adjust much ment Sect 3 2 4 Air intake restricted Clean a...

Page 15: ...oints Engine races stop Too much fuel caused by I engine immediately Disconnected governor by pushing throttle mechanism lever Engine stops Emergency shutdown unexpectedly circuit operated I Internal...

Page 16: ...j P Ii1 iz mop I ln rrf l l _ n OAKE u l U J _ 6 IL S 1 l I l s U t i W ii p r t l Engine misses at light load See Sect 3 2 4 Improper choke operation Clean cylinders See Heavy carbon deposits in Sect...

Page 17: ...tight i Defective ignition sys tem Adjust lash Sect 3 7 1 See Trouble Shooting Chart 4 Engine backfires Excess oil con sumption light blue smoky exhaust Lean fuel mixture Clogged fuel screen Adjust c...

Page 18: ...nder load Fuel mixture too rich Choke not open i Clogged air intake I RE MEDY Inspect engine check for clogged crankcase breather Inspect oil seals Sect 3 9 2 2 and Sect 3 9 5 5 Check for clogged cran...

Page 19: ...lace bearings knock bearing Low oil supply Add oil check for cause of low oil Sect 3 5 Oil badly diluted Replace oil Pinging sound Carbon in cylinder Remove carbon when engine is suddenly or Spark too...

Page 20: ...ct the generator wiring diagram a ing to the model phase and number of output wires Select the citer wiring diagram from the Magneciter model number on the p nameplate For revolving armature plants se...

Page 21: ...ing System HI The cooling system on the MJA MJB and MJC generating plants is a liquid coolant pressure circulating open type system that uses raw coolant city water sea water NOTE Factory installed he...

Page 22: ...air leaks 1 To measure water flow install a tank of kl 1 wn quantity at the water outlet Run the engine until the thermostat opens and thEm measure the length of time necessary to fill the tank From t...

Page 23: ...g system run the engine insert the cooling system outlet into a tank of water and watch for bubbles If bubbles appear inspect the cooling system thoroughly to find the source 3 1 3 REPAIR Whenever mak...

Page 24: ...vailable either factory installedoI as a kit for customer installation A completed heat exchanger install 3 tiQIJ contains 2 water systems the closed water system and raw water sys V 1 1 1 rIo V J J L...

Page 25: ...ds after the centrifugal switch has closed If ile plant automatically shuts down determine and correct the ause and then restart by pushing thE reset button on the emer ency relay The re set button wi...

Page 26: ...Shing is completed check the system thoroughly for leaks uncovered by the cleaning operations CONTROL SYSTEM For disassembly and repair of the timing gear and switchop erating mechanism see Sect 3 3 6...

Page 27: ...ch contact gap at 020 in Fig should become clogged remove the ends and clean out the tubes 3 1 4 5 Centrifugal Pump Repair The centrifugal fresh water pump is mounted on the heat exchanger bracket If...

Page 28: ...r replace The gap with the plant stopped should be maintained at 020 in Clean and flush cool For a complete description and repair instructions see Sect ing system and6 3 1 4 Replace thermostat 6 3 TE...

Page 29: ...lier ldels See Sect 6 3 3 4 1 pressure occurs the pressure switch closes completing the H circuit Thls operates the relay disconnecting engine ignition which stops the plant The centrifugal switch is...

Page 30: ...s are all current replacement parts The epoxy filled solen are identified by two part numbers stamped on the bottom thE style solenoids h ve only one number stamped on the housing Improper use If the...

Page 31: ...Y STYLE FIG 6 B OVERTIGHTENED START SOLENOID CONNECTIONS FUEL SYSTEM If fuel is stored for any great length of time it can oxidize and form gums the fuel becomes stale ONAN recommends changing fuel st...

Page 32: ...he cover and lift out the valve and cage assemblies 5 Drive out the rocker arm hinge pin 6 CONTROL SYSTEM The plant control system controis starting stopping battery n ing and provides a means of emer...

Page 33: ...Fuel pump failure is usually due to a leaking dia phragm valve or valve gasket A kit is available for replacement of these parts Because the extent of wear cannot be detected by the eye replace all p...

Page 34: ...ening the choke plate 3 2 4 l Adjustment Electric Choke Under normal operation adjust the choke so the distance measured between the choke plate and carbu retor throat Fig 3 2 E is as shown in the tab...

Page 35: ...ay be necessary to readjust the choke for best operation For more chOking turn the cover clock wise for less choking turn it counterclockwise 3 2 4 2 Disassembly and Repair Electric Choke If the choke...

Page 36: ...sition NOTE If a voltmeter isn t available use the above procedu mark the point where arcing begins Fuel enters the carburetor through the inlet valve Fig 3 2 G and pas ses into the float chamber To c...

Page 37: ...n FUEL SYSTEM adjusting needle As the throttle is opened to increase power it grad ually exposes the idle transfer port and fuel is drawn out through this port also As the engine governor opens the th...

Page 38: ...stop pin with the plant operating at no load This pre ents excessive hunting when a large load is suddenly remo ed 3 2 5 2 Remo al and Disassembly 1 Remm e the fuel line gO ernor linkage and electric...

Page 39: ...ntrol box and float should fit freely on its connections If a defective coil is found disassemble the gen pin without binding Invert ect 5 4 and replace the defective coil the c arburetor body and mea...

Page 40: ...ency Atthe time engine speed determines generator output voltage so volta be adjusted over asmaU range by adjusting thegovernormechan The voltage drop from no load to full load operation is determine...

Page 41: ...icker with the average load on the plant Set gap at 025 FIG 6 C ANTI FLICKER BREAKER POINT GAP FUEL SYSTEM 3 2 7 EXHAUST SYSTEM The exhaust system is normally supplied by the user and installed in the...

Page 42: ...eries indings act as the starting motor field The shunt ings are the working field they produce the magnetic field in w the armature turns to produce useful output NOTE Beginning Spec F 5MJB plants us...

Page 43: ...bUild up wltage slow to build en to twenty per cent ated voltage uter I roltage builds up nor LIt less than rated after build up loltage builds up nor ith slIghlly less than lItage at no load and age...

Page 44: ...d checking the ignition breaker point gap i u J1 C ircuil breaker opens i iaGout five seconds checking and cleaning spark plugs t C I OutJlutvoltage slow to build ins pecting both the low and hi tensi...

Page 45: ...e engine can be timed either stopped or running at rated speed With the engine stopped timing should be set for ignition at 50 ATC with the engine running at rated speed 250 BTC Always adjust the brea...

Page 46: ...tion breaker points 3 Remov e the 2 capscrews holding the breaker plate assembly and pull off the plate 4 Pull out the cam and weight assembly spacermaunted on the gear shaft Be careful not to lose th...

Page 47: ...4 0 4 5 stall lead Bl on the adjustable resistor plete assembly must be replaced Clean FIG 3 3 E CENTRIFUGAL and inspect the bearing surfaces in the WEIGHT SPRING DATA UTION Check this lead to see tha...

Page 48: ...10000 ohms for the secondary winding E tremely low resistance usually indicates a shorted winding and extremely high resistance usually indicates an open in the winding WARNlNG The 4 volt coils MJB M...

Page 49: ...make coil ahd WindiIlg testers for Which test data is available 3 3 4 MJC IGNITION SYSTEM TheMJC generating plant uses a suppressed battery ignition system with dual breaker points to produce and dist...

Page 50: ...wever they may be checked for proper timing by plac inga timing mark on the flywheel 1800 from the TC mark Then re peat steps 1 5 substituting cylinder 2 101 cylinder 1 and the new timing mark for TC...

Page 51: ...eel 3 If the timing pointer on the gear cover indicates 250 BTC timing is correct Otherwise loosen the distributor body clamp and rotate the distributor body to adjust timing If timing is early 250 ma...

Page 52: ...J Replace the rotor if it is grounded or has an open circuit or short 4 3 2 2 stator Continuity Tests Disconnect the generator output leads in the control box Use the wiring diagrams in Sect 10 to de...

Page 53: ...ng solvent When dry in spect all components Inspect the centrifugal advance component for signs of wear and replace any that appear WOrn or otherwise damaged Inspect the cam and shaft for wear or scor...

Page 54: ...d mesh the distributor and cam shaft gears 3 Install tbe distributor clamp screw right side of the plate and swing the assembty outward Tore move the brush holders unscrew the 4 machine screws on the...

Page 55: ...il maintenance should include inspecting and tightening the terminals and cleaning them if necessary A quick check for possible coil failure can be made by simply discon necting the high tension spark...

Page 56: ...conll winding less current in the gate winding and generator field and output voltage Next we must introduce a regulator so that the current in the cor windings will depend on the voltage output of t...

Page 57: ...ent actor allows to flow in the gate winding is dependent on the amount gnetism in the core The current flow increases the gate open there is more magnetism in the core until finally when the core ura...

Page 58: ...d to the engine crankcase througb the en to generator adapter The rotor is directly connected a taper with key to the engine crankshaft A ball bearing housed in the genera tor endbeU supports the outb...

Page 59: ...ain bearing support requires ement the whole crankcase must be replaced or returned to the Y to have a new housing fitted CENTER MAIN BEARING CAP ARING HALF BOLT SIDE MARKED FRONT I TOWARD CRANKSHAFT...

Page 60: ...3 1 5 volying 63 59 60 45 90 1770 1830 1770 18S0 3 48 51 49 52 1 I IArm 50 ature 1440 1530 1470 1560 90 3 2 E e _ 6 59 3 64 57 60 60 valying 90 1920 17 Z 9r fl8 3 Q 1770 4f i1 4 3 1 54 Field 50 1410 j...

Page 61: ...air Check all journals for out of round grooving or ridges Pay particular attention to ridges or grooves her side of the oil hole areas Unusual conditions here often point vious neglect of oil cleanli...

Page 62: ...specified the bearings show cracks breaks burrs excessive wear or a defects The camshaft to bearing clearance should be 0012 to 0037 check the rear bearing remove the expansion plug at the rear 0 cran...

Page 63: ...HOLES FRaN BEARING i FIG 3 9 E CAMSHAFT BEARING INSTALLATION OIL SYSTEM 3 5 1 MAINTENANCE Periodic oil system maintenance should include changing crankcase oil cleaning the crankcase breather Sect 3 5...

Page 64: ...oryoke so the smooth side is toward governor 3 Turn the governor cup so the stop pin in the gearc over will one of the holes in the cup surface Fig 3 9 B Measure th tance from the end of the stop pin...

Page 65: ...s in place Fig 9 B i I 11j INSTALL OIL SEAL FLUSH WITH THIS SURFACE THIS SURFACE MUST BE CLEAN BEFORE INSTALLING SEAL FIG 3 9 C GEAR COVER OIL SEAL OIL SYSTEM 3 5 6 OIL FILTER The full flow filter is...

Page 66: ...To install a new ring gear place TO it in an oven heated to 380 4000 LOOSEN FLYWHEEL F for 30 to 40 minutes CAUTION DON T HEAT WITH A TORCH When heated properly the ring will fall into place on the fl...

Page 67: ...es cylinder condition Worn cylinder walls Refinish cylinders and pistons replace pistons Leaky head gasket Replace head gasket ton and cylin Operated with dirty air Change air cleaner and ring wear cl...

Page 68: ...rmature 3 6 2 TESTING Poor cranking performance can be caused bya faulty starting motor defective battery insufficient capacity battery or high resistance in the starting circuit STARTING MOTOR l r ri...

Page 69: ...n 1 290 and 1 225 If not recharge the bat tery If the battery won t recharge replace it With the starting motor operating check the voltage drops 1 from the battery ground terminal post not the cable...

Page 70: ...Pistons and rings are available in 010 020 and 030 size If the cylinders don t need refinishing remove any exi ting riOg the top of the wall with a fine stone 3 8 3 PISTONS Thoroughly clean and inspe...

Page 71: ...y 3 6 4 REPAIR STARTING MOTOR 3 6 4 1 Armature Inspect the armature for mechanical defects before checking for grounds or shorted coils To test for grounds use a 12 volt test lamp and check between ea...

Page 72: ...are absorb ent bearings designed to hold up to 25 of their own weight in oiL Be sure the felt oil pad is in the outer end of the commutator end bearing When the motor is assembled check the armature e...

Page 73: ...and 12 as aear 07 as possible Adjust the link screw on the end of the solenoid plunger for proper clearance NOTE On plants built before March 1962 it was necessary to main tain the gap between ring ge...

Page 74: ...encil marks at intervals b valve face and observe if the marks rub off uniformly when valve is rotated part of a turn in the seat If the seat isn t t regrind the valves 4 Using a valve spring compress...

Page 75: ...nder head assembly contains valves valve seat inserts and guides rocker arms and spark plugs The valve assem blies are operated by pushrods running through the cylinder block to the camshaft Exhaust v...

Page 76: ...s assem le the valve ass bhes f 4 F t r i L 3 7 4 REPAm Thoroughly e1ean aU comp Ohentg 61 tl1e cylinder head assemblies Remove ail the carbon depOSits from the combustion chambers an clean all gasket...

Page 77: ...1 Be cylinder head assemblies Remove all the carbon deposits from the combustion chambers and Clean all gasket surfaces 3 7 4 1 Valves Remove all carbon and check each valve for burn ing pitting or w...

Page 78: ...d no valve seals 3 7 Cylinder Heads and Valves Each cast iron cylinder head assembly contains valves valve seat inserts and guides rocker arms and spark plugs The valve assen bUes are operated by push...

Page 79: ...the valve is rotated part of a turn in the seat If the seat isn t tight regrind the valves 4 Using a valve spring compressor compress each valve spring with its spring retainer in place and insert th...

Page 80: ...nion stop Fig 3 6 D This should be between 07 and 12 a 07 as possible Adjust the link screw on the end of the solenoi plunger for proper clearance NOTE On plants built before March 1962 it was necessa...

Page 81: ...designed to hold up to 25 of their own weight in oil Be Ere the felt oil pad is in the outer end of the commutator end bearing hen the motor is assembled check the armature end play It should betv ee...

Page 82: ...e reinstalle position the starter correctly 3 6 4 REPAIR STARTING MOTOR 3 6 4 1 Armature Inspect the armature for mechanical defect before checking for grounds or shorted coils To test for grounds use...

Page 83: ...er size If the cylinders don t need refinishing remove any existing ridges frQn the top of the wall with a fine stone 3 8 3 PISTONS Thoroughly clean and inspect e ach piston Clean the carbon from the...

Page 84: ...nder using a ring compressor tool Each assembly should be installed Check the charge condition of the battery with a hydrometer SPI gravity should be between 1 290 and 1 225 If not recharge the tery I...

Page 85: ...e start disconnect relay is rod Fig 3 8 D ergized Theover running clutch protects the starter armature from 1 i erspeeds 6 1 MAINTENANCE riodicallychecktbe starting circuit wiring for loose or dirty c...

Page 86: ...ket Refinish cylinders replace pistons Replace head gasket Clogged oil passages Clean all lines oil passages Piston and cylin der and ring wear Operated with dirty air cleaner Change air cleaner servi...

Page 87: ...e screws holding the gear COVer to the crankcase To loosen the gear cover tap itwith a soft hammer capscrews to pull the flywheel 3 9 1 1 Ring Gear To remove the ring gear if damaged s w part way thro...

Page 88: ...or binding and see that thegovernor shaft end thrust ball is in place Fig 3 9 B I I 1 tJ INSTALL OIL SEAL FLUSH WITH THIS SURFACE THIS SUR ACE MUST BE CLEAN BE ORE INSTALLI NG SEAL FIG 3 9 C GEAR COVE...

Page 89: ...r will fit into one of the holes in the cup surface Fig3 9 B Measure the dis tance from the end of the stop pin to the mounting face of the cover n should be 25 32 in If it isn t replace the 4 Use the...

Page 90: ...lA 1 I t CEN ER BEARING PRESS BEAR1N F LUSHWITH FRONT CRANK CASE SURFACE LlGNOIL HOLES FRON I 8EARIN I i 1 G i I 1 FIG 3 9 E CAMSHAFT BEARING INSTALLATION OIL SYSTEM 3 5 1 MAINTENANCE Periodic oil sys...

Page 91: ...breaks burrs excessive wear or other defects The camshaft to bearing clearance sbould be 0012 to 0037 To check the rear bearing remove the expansion plug at tbe rear of the crankcase Press new bearin...

Page 92: ...oughly clean the crankshaft and blowout all oil passages with compressed air Check all journals for out of round taper grooving or ridges Pay particular attention to ridges or grooves TROUBLE Speed to...

Page 93: ...3 Q 1770 3 90 2 60 50 54 1620 41 1410 5r 4 1c O l47D 3 90 1 30 I I c cc i i Numbers in pa reri s _ar PJ ant speed in rpm FIG a 4 B FRl QUEN AND SPEED TABLE I1 NtilNE IHSASSE MBLY 91 REAR BEARING PLAT...

Page 94: ...to the factory to have a new housing fitted BOLT CENTER MAIN IJ lr S DE MARKED FRONT BEARING CAP I TOWARD CRANKSHAFT I j GEAR BEARING HALF J O J i PLACE UPPER BEARING HOUSING HALF IN POS CRANKSHAFT l...

Page 95: ...ugh the engine to generator adapter The rotor is directly connected a tapered fit with key to the engine crankshaft A ball bearing housed in the genera tor endbell supports the outboard collector ring...

Page 96: ...nd a control winding The amount of current the reactor allows to flow in the gate winding is dependent on the amount of magnetism in the core The current flow increases the gate open when there is mor...

Page 97: ...field and a lower output voltage Next we must introduce a regulator so that the current in the control windings will depend on the voltage output of the generator The reg ulator must allow little or n...

Page 98: ...3 3 4 4 MTClgnition Coils The MTC generator uses two suppre ignition coils mounted on the intake manifold Normal ignition coi maintenance should include inspecting and tightening the terminals cleani...

Page 99: ...nnect the coil leads to the breaker point cover adapter See ect 3 3 H Ii REVOLVING FIELD G ENERATOR rightsideo f the plate and swing the assembly Qutward Tore move the brush holders unscrew the 4 mach...

Page 100: ...s except the conde1 breaker points and bushings in light cleaning solvent When dry i spect all components Inspect the centrifugal advance component f signs of wear and replace any that appear worn or...

Page 101: ...or short 4 3 2 2 Stator Continuity Tests Disconnect the generator output leads in the control box Use the wiring diagrams in Sect 10 to de termine the output lead coding 1 Using either the test lamp o...

Page 102: ...a multirfJeter IGNITION SYSTEM 2 Run the plant at rated speed Aim the flashing timing light tow the flywheel 3 If the timing pointer on the gear cover indicates 250 BTC timi correct Otherwise loosen t...

Page 103: ...0 from the TCmark Then re eat steps 1 5 substituting cylinder 2 1m cylinder 1 and the new ming mark for TC Later flywheels have BC Bottom Center mark iming Engine Running IstaHan automotive timing lig...

Page 104: ...d fails to ate it should then be tested on anyone of the popular make c windi 1g testers for which test data is available 3 3 4 lIIfJC IGNlTION SYSTEM The lIIfJC generating plant uses a suppressed bat...

Page 105: ...range from 5 2 ohms for the priInary inding and froIn 4000 10000 ohIns for the secondary wind ng emely low resistance usually indicates a shorted winding and Ktremely high resistance usually indicate...

Page 106: ...nd out without catching in CJ ml IU either end position Inspect the gear ramp for notches or other defects If any part of DIMENSION TENSI A INPOU the cam weight and gear assembly sticks the complete a...

Page 107: ...crews holding the breaker plate assembly and ull off the plate ull out the cam and Weight assembly Be careful not to lose the Jacermountedon the gear shaft REVO L VIN G FTELD GKN ERA TORf 05 TROUBLE S...

Page 108: ...g see Sect 3 3 3 2 3 3 3 2 Timing The engine can be timed either stopped or run rated speed With the engine stopped timing should be set for i at 50 ATC with the engine running at rated speed 2So BTC...

Page 109: ...inglhe ignition timing NATURE OF PROBABLE CORRECTIVE TROUBLE CAUSE ACTION Gener ator will not build up Circuit breaker in off Reset and close breaker voltag or tripped po ition Open in ci rcuit iJreak...

Page 110: ...rol ReactOl and replace if defective Check wiring diagram for pularity of Com pouud windL s through Reactors A and Band test for continuity Check wiring diagram lor polarity or Corn pound winding 1hro...

Page 111: ...are the working field they produce the magnetic field in which the armature turns to produce useful output 1 NOTE Beginning Spec F 5MJB plants use a separate automotive start er rather than the serie...

Page 112: ...resistor is located on the right side of the control box If flicker becomes exceSSive adjust the resistor by moving its slider Adjust it for minimum flicker with the average load on the plant Set gap...

Page 113: ...sting the governor mechanism The voltage drop from no load to full load operation is determined by the engine governor sensitivity To adjust output voltage slightly within the range shown in Fig 5 D a...

Page 114: ...ect values If the windings are warm from running the resistance will be slightly higher than specified If the resist ance is high check for an open circuit in one of the parallel wind ings step 3 othe...

Page 115: ...e plant tin at no load This pre ents excessive hunting when a large load denly removed 2 Removal and Disassembly emo e the fuel line gm ernor linkage and electric choke wire emOve the 2 carburetor mou...

Page 116: ...tified by a chisel mark on the brush rig Fig 5 1 If Lhe mark is lost or a new brush rig installed follow these instructions to find the neutral position FUEL SYSTEM adjusting needle As the throttle is...

Page 117: ...ce draws fuel up thr ugh the hollow center lain adjusting needle through passages in the carburetor body ile port Bleed holes in the main adjusting needle allow air to I and mix with the fuel When the...

Page 118: ...less choking turn it counterclockwise 3 2 4 2 Disassembly and Repair Electric Choke If the choke not operate or won t maintain its adjustment disassemble it for pair If it won t close check for bindi...

Page 119: ...models of generating plants use an automatic electric Fig 3 2 A An electric element controls the automaztie electric Before the plant starts the choke is closed When the plant rted the generator suppl...

Page 120: ...ir Fuel pump failure is usually due to a leaking phragm valve ar valve gasket A kit is available far replacemer these parts Because the extent of wear cannot be detected by thE replace all parts in th...

Page 121: ...ge pin 60 CONTROL SYSTEM The plant control system controls starting stopping battery recharg ing and provides a means of emergency automatic stopping The con trol system and control system defects can...

Page 122: ...y MJB only Fig 6 A shows a start ing cycle To stop the engine the stop switch grounds the stop relay breaking the ignition coil circuit EARLY STYLE FIG 6 B OVERTIGHTENED START SOLENOID CONNECTIONS FUE...

Page 123: ...noids h ve only One number stamped on the Improper use If the start switch is released when an engine slows at the peak of the first compression stroke the large current pass through the solenoid may...

Page 124: ...MJB models See Sect 6 3 3 4 If low oil pressure occurs the pressure switch closes completing the relay coil circuit This operates the relay disconnecting engine ignition system which stops the plant T...

Page 125: ...d Centrifugal switch The centrif ugal switch is open when the plant is stopped During the starting cycle it closes when the plant speed reaches about 900 rpm The gap with the plant stopped should be m...

Page 126: ...h leads when the engine starts COOLINGSYS TE M 3 1 4 3 Repair and Testing Raw Water System Test for air I and insufficient water flow as described in Sect 3 1 2 Repair of rubber impeller pump was cove...

Page 127: ...ect 3 3 6 3 1 4 starting Solenoid 307B40 This solenoid is the same as that described in Sect 6 2 1 1 6 3 2 BATTERY CHARGING CIRCUIT This circuit in cludes the adjustable charge resistor j ectifier and...

Page 128: ...d to shut down the plant if oil pressure is not sensed by the low oil pressure switch within 15 seconds after the centrifugal switch has closed If the plant automatically shuts down determine and corr...

Page 129: ...eat exchanger installatlol 2 water systems the closed water system and raw water sys I J L 1 LJ 1t L i J t I J 1 L 10 f ing element on the relay a solder connection holding the spring loaded contacts...

Page 130: ...Air leaks are an important cause of premature impeller fail To test for air in the cooling system run the engine insert cooling system outlet into a tank of water and watch for bubb If bubbles appear...

Page 131: ...ecessary tofm the tank From this in the flow in gallons per minute GPM Minimum values are 9 lADLI ur LI AKA I All values in inches unless otherwise specified CAMSHAFT Bearing Journal Diameter Front Be...

Page 132: ...lts 420 Amps 7 8 lb ft Min 32 40 ounces with new brushes 3405 3415 001 003 450 019 See Fig 3 7 B 015 3405 3415 0025 0045 450 023 See Fig 3 7 B 020 1 25 32 4690 4695 467 468 344 345 342 343 3 1 Cooling...

Page 133: ...rd ingto the model phase and number of output wires Select the Magne citer wiring diagram from the Magneciter model number on the plant nameplate For revolving armature plants select the generator wir...

Page 134: ...ly Add oil chec k cause of low oi 3 5 Oil badly diluted Replace oil Pinging sound Carbon in cylinder Remove carbon when engine is suddenly or Spark too early Adjust breaker heavily loaded Retime spark...

Page 135: ...rings I Loose piston I l TO CONTROL eOl See Sect 3 2 4 t 111 MZ Clean air cleaner Sect 3 2 6 lI MI Replace bearing 4MJA Revolving Armature 3 Wire Sillgle Phase S I M TO Oo M 3 1 0 AI he Add oil REA t...

Page 136: ...t TROUBLE POSSIBLE CAUSE REMEDY Engine misfires Valve lash too tight Adjust lash Se at heavy load cont Engine backfires I Excess oil con sumption light blue smoky exhaust Defective ignition sys tern S...

Page 137: ...n See Sect 3 2 4 Heavy carbon deposits in cylinders I Clean cylinders See Sect 3 2 I F aulty carburetion See Trouble Shooting Chart 3 nisses load Spark plug gaps too narrow Set at 025 Intake air leak...

Page 138: ...Engine stops unexpectedly Clean air cleane Restricted air intake Low engine lPower Check back pres High exhaust back pres Sect 3 2 7 sure Water in gasoline I Change fuel i Inspect all gaskJ manifold...

Page 139: ...ect operating pro cedures or adjust choke hard to Restricted air intake Clean air cleaner Sect 3 2 6 Poor fuel Change fuel Defective ignition sys tem Incorrect timing Defective fuel pump Poor compress...

Page 140: ...fuel POSSIBLE CAUSE REMEI Battery discharged See Troubh i She Chart 7 Control circuit defective See Sect 6 Internal seizure f i Engine oil too heavy for I operation in low temper ature Disassemble en...

Page 141: ...cale 5 0 5 3 water flow gallons per minute 4 4 otiledi xhaust manl fold nO yes nand molded ibration mounts yes yes lm il e comnlend ed powertake off from uHey at any load 2 hp 2 hp take oll limit at r...

Page 142: ...x Check Fuel Supply x 9il Le e L x x _an Governor Linkaa Service Air Cleaner Silencer xt Chane e Crankcase Oil x Clean Crankcase Breather x Clean and Adjust Spark Plurrs x Check Breaker Points x Check...

Page 143: ...r is In r i I m m U til til U OJ 0 6 6 o x In In en I l I en i i i i I AI o C I r m I j 1 C 1 o r J 7z FE 1t b THBJ CDJiJ E N SER L __ I1lfiH EMF CUT our SWITCH WHEN USED LrCTRIC CHOKE r I N _ _ Q _ _...

Page 144: ...Q q ta I 0 I Q It l IJ j O 0 e l JJJl I rJ _ j o I JI w I Il t lII I I I 6 I i I _ c I I I a I i I I l I w I I I I I I I I Q I J lei I Jol l I al H j jJ lt I s OIL DRAIN HAUST OUTLET ADJUSTMENT FLp G...

Page 145: ...FuE L SOL NOfD o CtRculHD l VAL VE 1 TO EN ft t N U6 q l TO GEt lERATOR B2 I I 1 1 0 5 fl c J 1 vOl T I 1m I L t T IC FUEL 1 _ BATT R IPLI WfP I PM LLEC r II I _ol I _L ____ 1 I M V 6ED r CHaME f I I...

Page 146: ...e Revolving Field Residual Reset Switch Reverse Current Relay Revolving Armature Gener ator Armature Ball Bearing Brushes Commutator Field Commutator Collector Rings Resistor Charge Circuit Resistor E...

Page 147: ...rnor Arm Governor Governor Governor Shaft Governor Shaft Bearings Governor Governor Ball Brg Governor Yoke Beat Exchanger Hi Temp Switch Ignition Breaker Points 1 Cylinder 2 Cylinder 4 Cylinder Igniti...

Page 148: ...em 3 3 Ignition System 3 4 Governor System J 3 5 Oil System 3 6 Starting System 3 7 Cylinder Heads and Valves 3 8 Pistons Connecting Rods Cylinders 3 9 Engine Disassembly 4 GENERATOR REVOLVING FIELD 7...

Page 149: ...tandard Model cification Letter Advanceswith ONANchanges r JB Some models have generators reconnectiblefor either e L 2 or 3 these models are designated 3C MJB MJC AllCode 3 models are reconnectible f...

Page 150: ...s is what it was designed for But tion ONAN recommends that you study the whole It will help to acquaint you with the plants you ll ingon and save time later on in servicing If possible use a parts ca...

Page 151: ...If you need help with your old Onan visit the Smart Guys at The Stak They have many years of experience and they are happy to help http www smokstak com forum forumdisplay php f 1...

Page 152: ......

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Onan MJA Series, Service Manual

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