ONAN T260G ENGINE SERVICE MANUAL Table of Contents – Page 1 of 2 SAFETY PRECAUTIONS GENERAL PROTECT AGAINST MOVING PARTS BATTERIES FUEL SYSTEM EXHAUST SYSTEM EXHAUST GAS IS DEADLY! COOLING SYSTEM KEEP THE UNIT AND SURROUNDING AREA CLEAN INTRODUCTION EXHAUST GAS IS DEADLY! GENERAL INFORMATION INTRODUCTION ENGINE MODEL REFERENCE SPECIFICATIONS DIMENSIONS AND CLEARANCES ASSEMBLY TORQUES ENGINE TROUBLESHOOTING OIL SYSTEM CRANKCASE OIL OIL FILTER CHANGE CRANKCASE BREATHER PRESSURE LUBRICATION FUEL SYSTEM CARBURE
ONAN T260G ENGINE SERVICE MANUAL Table of Contents – Page 2 of 2 ENGINE DISASSEMBLY DISASSEMBLY/ASSEMBLY VALVE SYSTEM TAPPETS VALVE FACE AND SEAT GRINDING FLYWHEEL GEAR COVER GOVERNOR CUP TIMING GEARS PISTONS AND CONNECTING RODS CYLINDER BLOCK CRANKSHAFT BEARINGS CRANKSHAFT ENDPLAY CHECKING CONNECTING ROD BEARING CLEARANCE OIL SEALS PISTON ASSEMBLY INSTALLATION OF PISTON IN CYLINDER CYLINDER HEADS CYLINDER HEAD STUD TEST AND REPLACEMENT PROCEDURE ALIGNING BLOWER WHEEL, VENTURI AND CHAFF SCREEN
Service Manual Engine
Safety Precautions It is recommended that you read your engine manual and become thoroughly acquainted with your equipment before you start the engine. This symbol if used warns of immediatehazardswhich will resultin severe personal injuryor death. Thissymbolrefersto ahazard or WARNING unsafe practice which can result in severe personal injury or death. Thissymbolrefersto ahazard or CAUTION unsafe practice which can resultin personal injury or product or property damage.
Table' ofContents TITLE PAGE . l-1 .2-1 General Information Speclflcations.. Dimensions and Clearances Assembly Torques and Special Tools Engine Troubleshooting Oil System Fuel System Ignition and Battery Charging.. Starting System Engine Disassembly .3-1 .4-1 .5-1 .6-1 .7-1 .8-1 .9-1 .10-1 WARNING] EXHAUST GAS IS DEADLY! Exhaust gasesfrom all fuels (including diesel, gasoline, liquidpropane, natural gas) contain carbon monoxide, anodorless and colorless gas.
General Information INTRODUCTION This manual deals with specific mechanical and electrical information needed by engine mechanics for troubleshooting, servicing, repairing,or overhauling the engine. Use only Genuine Onanreplacement parts to ensure quality and the best possible repair and overhaul results. When ordering parts, always use the complete Model and Spec number as well as the Serial number shown on the nameplate.
Specifications This manual containsSI metric equivalents thatfollow immediately in parentheses after the U.S. customary units of measure.
Dimensions and Clearances All clearances given at room temperatureof 70°F (21 C) All dimensions in inches (approximate miilimetre dimensions in parentheses) unless otherwise specified DESCRIPTION 0.003 CYLINDER BLOCK Cylinder Bore Honed Diameter Maximum Allowable Taper Out-of-Round Main Bearing Inside Diameter (Without bearing) Main Bearing Inside Diameter (Installed) Camshaft Bearing Bore (Bearing Installed) Interference Stud Height from Top Surface ofBlock Spec C, D, E Top2 Middle (46.74) (48.26) 1.
DESCRIPTION MINIMUM Inches (mm) MAXIMUM Inches (mm) PISTON Clearance in Cylinder Measure 1.187Below Top of Piston and 90" from pin . . .. Piston Pin Bore.. . . . . . . . . . . . .. . . . . , ... ... .. Ring Groove Width Top 1 Compression Ring . . . . . . .. . . . . . . .. No. 2 Compression Ring.. . . . . . . . . . .. . . .. . .. . . , No. 3 Oil Control Ring . . . . . . . . . . , . . . . . . .. . . . .. . . .. . . .. . . . . . .. .. . . . . . . . . .. . . . . . . . . . . .. . . . . . . . . . . . . .. .
DESCRIPTION MINIMUM Inches (mm) GEAR BACKLASH Timing Gear Spec A-E Begin Spec F Oil Pump Gear spec A-E Begin Spec F GOVERNOR Dashpot to Governor Arm Bracket.. 3- 3 MAXIMUM Inches (mm) 0.002 0.001 (0.051) (0.025) 0.003 0.005 (0.076) (0.127) 0.002 0.001 (0.051) '(0.025) 0.005 0.008 (0.127) (0.203) 0.040 (1.02) 0.060 (1.
Assembly Torques The torque values given in Table 1 have been determined for the specific applications. Standard torque valuesmust not be used where those listed in Table 1 apply. The engine assembly torques given here will assure proper tightness without danger of stripping threads. All threads must be clean and lubricated with new engine oil before torquing. Check all studs,nuts, and capscrews, and tighten as required to keep them from working loose.
Engine Troubleshooting I IGNITION SYSTEM FUEL SYSTEM INTERNAL ENGINE COOLING SYSTEM (AIR COOLED) THROTTLE AND GOVERNOR M-1686-1 5-1
Oil System Oil level should be to the FULL mark ofthe dipstick. Start engine and run for a short time to check for oil leaks around the drain plug. CRANKCASE OIL Refer to engine nameplate or Periodic Maintenance Schedule, located in theOperator'sManual,for oil change interval. If operating in extremely dusty, high ambient, or low ambient conditions change oil more often. Run engine until thoroughly warm before draining oil.
Apply a thinfilm of oil to the gasket. Spin element down by hand until gasket just touches mounting pad and then turn down an additional 1/2-3/4 turn. Do not overtighten. Clean orreplace crankcase breather baffle periodically. Be sure baffle material-doesn’tcome apart and work into manifold. the To disassemble, remove breather hose from cap and valve assembly. Remove cap and valve assembly and wash in asuitable solvent. Replacecap and valve if balls do not move freely.Pull baffle out and wash in solvent.
Circumferential grooves in the main bearings supply The valve is non-adjustable and normally does not oil to connecting rod bearings through drilled pasneed maintenance. Determine if valve is operating -.,sages from eachmainjournal. A drilled passage normally by inspecting plunger action as follows: \connects thefront mainbearing oil supply t o the front 'camshaft bearing; rear cam bearing is splash lubrica1 . Remove the 3/8 x 24 x 7/8 cap screw located ted.
Fuel System CARBURETOR Set the adjustment screw about 1/8 turn outward (rich) from the midpoint of this range. On Nikki carburetors the idle adjustment is limited to 1/8 turn.Do not go beyondtheselimits. The carburetor mixture screw settings weresetfor maximum efficiency at the factory and should normally not be disturbed. If adjustmentsseem necessary, first be suretheignition system isworkingproperlyand governor sensitivity is properly adjusted.
In general, overhauling a carburetor consists of disassembly, a thorough cleaning, and replacement of worn parts. Carburetorrepair parts are available. THROTTLE STOP SCREW General instructions for overhauling a carburetor are given below. Carefully note the position of all parts while removing to assure correct placement when reassembling Read through all the instructions before beginningforabetterunderstanding of theprocedures involved. Carburetor componentsare shown in Figure 3.
RemovalRepair and 1. Remove air cleaner and hose. 2. Disconnect governor and throttle linkage, choke control and fuel line from carburetor. 3. Remove the four intake manifold cap screws and lift complete manifold assembly from engine. 4. Remove carburetor from intake manifold. Cleaning 1. Soak all metal components not replaced in carburetor cleaner. Do not soak non-metal floats or other non-metal parts. Follow the cleaningmanufacturer’s recommendations. 2.
Reassembly and Installation (Walbro) 1. Install needlevalveand seat, main jet and fioat assembly. Makesure that float pivot pin is properly placed and that float moves freely without binding. 2. Gently push float tang down until needle just seats. (Figure 4). Measure float level; adjust if necessary. Release float tang and measure float drop; adjust if necessary.When checking float level anddrop, measure to float body, not seam. 3.
3. Connect a vacuum gaugefuel topump inlet using a piece of fuel hosewith clamps. 4. Start engine and allow to idle. foratleast seconds. Record vacuum gauge reading. five 5. Move throttle control to high idle position. Wait at leastfivesecondsandrecordvacuumgauge reading. Fuel Pump Repair This section applies only to Facet fuel pump. TheNikki fuel pump is notrepairable; replace unit if test readings are notwithin the values specified in TABLE 1. 1. Remove the vacuum and fuel lines.
1. WASH 2. SQUEEZE DRY 3. COAT WITH OIL 4. INSTALL OVER PAPER ELEMENT POLYURETHANE PRE-CLEANER SAFETY COVER FS-1131 FIGURE 7. AIR CLEANERASSEMBLY 2. Depending on conditions in which the engine is operating, theinnerpaper element shouldbe replaced whenever it becomes excessively dirty or oily. 2. Holding throttle against throttle stop screw, adjust dashpot to obtain 0.050 inch (1.27 mm) clearance (Figure 8). 3.
GOVERNOR ADJUSTMENT THROTTLE STOP SCREW These engines are adapted for use wherea wide range of speedsettings is desired. Engine speed is controlled atany given point betweenminimumandmaximumby simply shifting the throttle lever on the dash panel until the desired speed is reached. CARBURETOR THROTTLE PLATE A reliable instrument for checking engine speed is required for accurate governor adjustment. Engine speed can be checked with a tachometer.
Ignition and Battery Charging ! BREAKER POINT IGNITION SYSTEM This section applies to those engines equippedwith an automotivetypebattery ignition system.Bothspark plugsfire simultaneously, thus the need for distributor a is eliminated. To maintain maximum engine efficiency, change the breaker points every 200hours of operation. 7. Replace breaker box cover, coil wire, spark plugs, and spark plug cables. Continuity Test As a check for proper ignition timing a continuity test may be performed: 1.
WARNING Failuretogroundsparktester away from spark plug hole may result in ignitionof cylinder gases andmay cause, severe personal injury. ELECTRONIC IGNITION SYSTEM This section applies to those engines equipped with an electronic battery ignition system. Both spark plugs fire simultaneously, thus the need for a distributor is eliminated. The electronic ignition module is located on the engine gear cover behind the flywheel.
T h e ignition timing is preset at the factory and is not adjustable. Fortroubleshooting purposes, it is possible to make an approximate check of the ignition timing by removing blowerhousingandusingthe gearcase timing marks. 4. Rotate the flywheelslowly by hand in the clockwise direction until the voltmeter reading jumpsfrom approximately 1 volt to battery voltage.
SPARK PLUGS BATTERY JUMP STARTING Checkandregap spark plugs every 100 hours of operation (Figure 6). Replace spark plugs that show signsof fouling or electrodeerosion. Occasionally,it may be necessary to jump start(charge) a weak batteryusing a charged boosterbattery. If jump starting is necessary, the following procedurerecom is mended in order to prevent starter damage, battery damage and personal injuries.
FLYWHEEL ALTERNATOR This unit is equippedwith a permanent magnetflywheel a l t e r n a t o r and solid-state voltage regulator-rectifier ,output control). See Figure 9. As with all solid-state electrical units, precautions are necessary when servicing. Observe the following: This engine uses a 12 volt, negative CAUTION- ground CAUTION system.Alternatormustbe connected to battery atall timeswhenengineis running. Do not reverse battery cables. 2.
With the engine running between 1800 to 2600 rpm, observe the panel ammeter (if not already equipped, connect atestammeter). If no charging is evident, proceed with the AlternatorOutput Test. and from battery negative terminal to regulatorrectifier case. If battery voltage remains low with engine running, proceed tostep 3. 3. Disconnect plug from regulator-rectifier and test the AC voltage atthe plugwith engine running near 3600 rpm.
8-7
ENGINE WIRING DIAGRAM (Solenoid Shift Type Starter) 8-8
Starting System ELECTRIC STARTER 2. Disconnect battery cable and electrical lead wires from starter. Normally the starterwill require little or no service other than possible brush replacement.However, if through accident ormisuse, the starter requires service or overhaul, the following information will provide the information necessary to perform this service. 3. Remove blower housing and cylinder airhousing. 4. Remove flywheel andstartermotor.
StarterDisassembty (Solenoid Shift Type) 2. Assemble brushes so thatthechamferedside is away from the brush springs. Make sure brush wires do not rub against commutaor the or endcap. 1. Remove “M”terminalnutandwireleadfrom solenoid (Figure 2). 3. Torque brush screws to a valueof 3 to 3.5 ft-lbs (4 to 5 Nm). nut stud 4. input Torque 7 Nm). of valueto a 2.Remove the two solenoid mounting screws and remove solenoid. 4 to 5 ft-lbs (5 to 5. Apply a thin film of grease to the commutator end of3.
8. Push stopper toward pinion andremove snap ring (Figure 3). Removestopperandoverrunningclutchfrom armature shaft. \ STOPPER SNAP RING ES-1194 FIGURE 4. INSTALLING STOPPER Es-1622 4. Lubrication: When starter motoris assembled apply grease to each of the following points (Recommended grade: Multemp PS No. 2): FIGURE 3. REMOVINGOVERRUNNINGCLUTCH Armature shaft spline Both bushings (Both ends of armature) Stopper on armature shaft Pinion gear 'Sliding portion of lever 10.
10. Install and tighten the two throughcapscrews. 11. Install soienoid plungerin lever. Securesolenoid to front bracket with two machine screws. 12. Install wire lead to the terminal “M”on solenoid. 13. Afterassembly,adjust pinion clearance. Pinion clearance should be 0.020 to 0.080 inch (0.5 to 2.0 mm); if not, check as follows. See Figure 5. A. Connectstarter to a battery, as shown in Figure 5. Close switch. This willshift pinion into cranking position. B.
Commutator Inspection: If commutator is dirty or discolored, clean with number 00 to 000 commutator paper. Blow grit out of armature aftercleaning. Check for shorts between positive side of brush holder and brush holder base. If there is continuity, replace holder assembly. Check for free movement of brushes. All brushes should move freelyin the brush holders. commutator is scored, rough, or worn, turn it down in a lathe. Overrunning Clutch: Inspect pinion and spline teeth for wear or damage.
Brush Replacement:Cut old positive brush from pigtail at the brush. Be careful not to damage field coil. Clean 1 / 4 to 3/8 inch (6.5 to 9.5 mm) of brush end of pigtail with sandpaper or emerycloth (Figure 11). FLYWHEEL RING GEAR 0.020 0.015 inch (0.51 0.38 mm) STARTER GEAR FREE TRAVEL WHEN ENGAGED WITH FLYWHEEL GEAR PIGTAIL STILL ATTACHED TO FIELD COIL SMALL CHAMFER (approx.
another EngineDisassembly DlSASSEMBLY/ASSEMBLY 1. Use the proper bearing driver to install front main bearing after coating it with a light film of oil. 2. Insertrearmain bearing in rear bearing plate. 3. Insert crankshaft, rear bearing plate, and crankshaft When complete enginedisassembly is necessary, first remove all completeassemblies. Individual assemblies such as fuel pump and carburetor can bedisassembled at and repaired 4. Install piston and connectingrods. 5.
VALVE SYSTEM Tappet Adjustment Theengine isequipped with adjustable valve tappets. The valve tappet clearance should be checked and adjusted, if necessary, at least every 200 operating hours or when poor engine performance is noticed. Adjust the valve clearance only when engine is at ambient temperature. Proceed as follows: 1. Remove ignition key to prevent accidental starting. 2. Remove all parts necessary to gain access to valve tappets. 3.
Warpage occurs chiefly in theupper stem due to its exposure to intense heat. Out-of-round wear follows when the seat is pounded by a valve whose head is not in line withthe stem and guide. If a valve face is b u r n e d or warped, or if the stem is worn, install new a 'valve. Driving out old guides can damage CAUTION the guide or tappet bores. Be careful not to strike guide bores with driver or allow guide to strike tappet bores during removal.
Valve Seat Removal: Remove carbon and combustion deposits from valveseat. Select proper puller size determined by inside diameter of valve seat. On some pullers use a new seat asa guide to adjust puller depth (Figure 4). Puller jaws must expand into cylinder block at the point where bottom of valve seat insert rests cylinder block. Position puller on valve seatand tighten hex nut. Clampcylinder block to a solid bench. Attach slide hammer to puller. Tighten hex nut between each blow with the slide hammer.
TAPPETS Refinish valve faces to a 44" angle on a valve refacing machine. The first cut fromvalve face must be a light Very little wear takes place on tappet diameters or in grinding. Check if there is an unevenness of metal tappet bores. If the clearance between tappet and being removed. If only part of valve's face has been in cylinder blockexceeds specifications, replace touched, check to see if valve is properly seated in he tappet. machine or if valve is warped, worn, or distorted.
FLYWHEEL GEAR COVER Removing theflywheel is a relatively simple process, but the following procedure must be followedto avoid damage to the gear case and possible injury to the operator. After removing the mounting screws, tap the gear cover gently with a soft faced hammer to loosen it. When installing the gear cover, make sure that the pin in the gear cover engages the nylon lined (smooth) hole in the governor cup (Figure 9).
ASSEMBLED THE DIMENSION SHOWN ON DRAWING WILL BE AS INDICATED CAMSHAFT GEAR RIGHT WRONG C-1107 INSTALLATION OF BALL SPACER CENTER SNAP RING GOVERNOR CUP CAMSHAFT GOVERNOR FLYBALL 5 BALL GOVERNOR 6 BALL GOVERNOR 8 BALL GOVERNOR LOCATIONS FLYBALL CS-1238 FIGURE 10. GOVERNOR CUP DETAILS GOVERNOR CUP nwITH the gear cover removed, the governor cup cannot be pulled outward or removed without damage. If the center pin extends out too far, the cup will not hold the flyballs properly.
CRANKSHAFT 4. Turn the crankshaft until the piston is at the bottom of its stroke and remove the connecting rod nuts. Lift the rod bearing cap from the rod and push therod and piston assembly out through the top of the cylinder usinghammer a handle. A v o i d scratching the crankpin and cylinder wall whel removing the piston and rod. GEAR PULLER 5. Mark each piston and rod assembly so they can be returned to their respective cylinders after overhaul.
FIGURE 15. CHECKINGRINGSIDECLEARANCE with deep nicks, signs of fractures, scored bores or bores out of round more than 0.002 inch. 2. Use a new piston pin to check connecting rod for wear. A push fit clearance is required and varies from engine to engine. If a new piston pin falls through a dry rod pin bore as a result of its own weight, replace the rod. FIGURE 14. PISTONGROOVECLEANING Fitting Pistons: Inspection 1. Proper piston tolerances must be maintained for satisfactory operation.
Cleaning Fitting PistonRings: After removing pistons, crankshaft, cylinder heads, etc., inspect block for cracks and extreme wear. If block is still serviceable, prepare it for cleaning as follows: 1. Install the piston ring inthe cylinder bore. Invert the piston and push the ring to the end of ring travel, about halfway into the bore, which trues the ring end gap. Check the gap with a feeler gauge (Figure 17). 1. Scrape all oldgasket material from block.
A. Measure and record as “A” the cylinder bore diameter (parallel to crankshaft)near the top of cylinderbore where greatest amount of wear occurs. TOP END OF CYLlNDER B. Also measure and record as “B” cylinder bore diameter (parallel to crankshaft) at the bottom of piston travel. RING WEAR A REA C. Measure and record as “C” cylinderbore diameter (perpendicular to crankshaft) near thetop of cylinderbore where greatest amount of wear occurs. 0490 I BOTTOM OF RING TRAVEL D.
3. Clean base of boring bar before bar is set up. Deposits underboring bar will cause it to tilt and the cylinder will be distorted after boring. 4. Make aninitial rough cut, followed by a cut. finish Then hone cylinder bore to the specifiedoversize. Deglazing Cylinder Bores Deglaze the cylinder bores if there are no scuff marks and no wear Or out of round beyond specifications before installing new rings.
CRANKSHAFT C l e a n crankshaft thoroughly and inspect journals for scoring, chipping, cracking, or signs of overheating. If crankshaft has overheated, is scored, or excessively worn, reconditioning or replacement will be required. Examine bearing journals for cracks if overheating has occurred. ALIGN HOLE IN BEARING Measure crankshaft main bearing and connecting rod journals at several places on their diameter to check for roundness and taper. 7/32”(5.
REAR BEARING END PLATE LOCK PIN In the rear bearing plate, install the bearing flush to 1/64 inch (0.40 mm) below the endof the bore. Be sure to alignthe oil holes in the bearing with the oil holes in the bearing bore (Figure 21). The oil passage must be least half open. Lubricate bearing after installation. If head of lock pin is damaged, use side cutters or Easy Out tool to remove and install new pin. Oil grooves in thrust washers must face the crankshaft, and washers must be flat (not bent).
CHECKING CONNECTING ROD BEARING CLEARANCE WITH PLASTIGAUGE 1. Make certain that all parts are marked or identified so that they are reinstalled in their original positions. Using aclean dry cloth, thoroughly clean all oilfrom crankshaft journal and connecting rod. 2. Place a piece of correct sizePlastigauge in the bearing capthe full width of thejournal surface and about 1/4 inch (6.35 mm) off center (Figure 24). 3.
PISTON ASSEMBLY Lubricate all parts with engine oil. Position piston on its respective rod andinstall the pin. OIL HOLE TOWARD CAMSHAFT Install the rings on thepiston’s starting with the oil control ring (Figure 26). Use apiston ring spreader to prevent twisting or excessive expansion of the ring.. Compression rings have a dot or the word “top” on one side of the ring to indicate which side faces the topof the piston. Unmarked piston rings can beinstalled either way.
CYLINDER HEADS ,Remove the cylinder heads for lead cleaning and gasket change at least every 250 hours, or when poor engine performance is noticed. 1. Use a 1/2 inch (13 mm) socket wrench to remove cylinder head nuts. Lift heads off. 6. Follow the head torque sequence shown in Figure 29 tightening all nuts to 5 ft-lbs (7 Nm), then 10 ft-lbs (14 Nm), then to the torque specified in the ASSEMBLY TORQUESsection. Recheck all nuts for correct torque. not torque or remove heads CAUTION Do when they are hot.
CYLINDER HEAD STUD TEST AND REPLACEMENT PROCEDURE This cylinder head stud replacement procedure should be used whenever replacing any of thetop six studs on the block. The use of Helicoil is not a recommended repair procedure. If aHelicoil has been used, the cylinder block must be replaced. Graphoil head and intake manifold gaskets should also be used when replacing cylinder head studs. HEAT TREATED NUTS COMPRESSION WASHERS Parts Required Part No.
On some engines, it is possible that groove a from the old head gasket fire ring may be impressed into thehead and/or block. If this is the case, it is essential thatthe part be replaced or milled to remove the imperfection. If all of the top six studs accepted 30 ft-lb of torque without pulling out,the new head gasket may be put on without replacement of the studs. If this is thecase, skip steps 6 through 12. 14. Blow out all residual debris andmetal chips using low pressure (35 PSI or less) air.
ALIGNING BLOWER WHEEL, VENTURI AND CHAFF SCREEN It may be difficult to line up thescrew holes in the blower housing chaff screen with thosein the venturi andthose in the blower wheel if these parts are separated without noting their relative positions.The holes will match up if the parts are aligned as shown in Figure 34. SCREW HOLES ALIGN THROUGH PART DIAMETER BLOWER WHEEL SCREW HOLES ALIGN THROUGH PART DIAMETER VENTURI CHAFF SCREEN POSITION PARTS WITH ALIGNED SCREW HOLES AT TOP FIGURE 34.
