Generac Power Systems GTV-990 Manual
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Generac Power Systems GTV-990 Manual

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Manual Part No. 0E2081
SERVICE
MANUAL
GTV – 990/760
V-TWIN
OHVI ENGINE
P. O. B ox 2 9 7 • W h i t ewa t e r, W I • 5 3 1 9 0
Phone: (262) 473-5514
Fax: (262) 472-6505
Draft Approved- 04/24/03
Printed in U.S.A

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Summary of Contents for Generac Power Systems GTV-990

  • Page 1 Manual Part No. 0E2081 SERVICE MANUAL GTV – 990/760 V-TWIN OHVI ENGINE P. O. B ox 2 9 7 • W h i t ewa t e r, W I • 5 3 1 9 0 Phone: (262) 473-5514 Fax: (262) 472-6505 Draft Approved- 04/24/03 Printed in U.S.A...
  • Page 2 FOREWORD This manual has been written and published by GENERAC ® POWER SYSTEMS, INC. to aid our dealers’ mechanics, company service per- sonnel and general consumers when servicing the products described herein. It is assumed that these personnel are familiar with the servicing pro- cedures for these products, or like or similar products, manufactured and marketed by GENERAC ®...

  • Page 3: Table Of Contents

    Generac parts and are listed as such in this manual. ATTENTION! Generac Power Systems does not approve or authorize the use of these engines on All Terrain Vehicles (ATV’s), go-carts, motorbikes, aircraft products, personal watercraft, or vehicles intended for use in competitive events.

  • Page 4: Rules For Safe Operation

    RULES FOR SAFE OPERATION RULES FOR SAFE OPERATION If you do not understand any portion of this manual, con- tact Generac or your nearest Generac Authorized Service Study these RULES FOR SAFE OPERATION carefully before Dealer for starting, operating and servicing procedures. operating or servicing this equipment.

  • Page 5: Service Information

    Service technicians are factory trained and • Generac Power Systems does not approve or authorize the capable of handling all service needs. use of these engines on All Terrain Vehicles (ATV’s), go-carts,...

  • Page 6: Dimensions And Features

    DIMENSIONS AND FEATURES...
  • Page 7 DIMENSIONS AND FEATURES...
  • Page 8 DIMENSIONS AND FEATURES...
  • Page 9 DIMENSIONS AND FEATURES...

  • Page 10: 4-Cycle Engine Theory

    4-CYCLE ENGINE THEORY If the engine is to run properly, four (4) events must occur in POWER IGNITION AND the proper sequence and at the correct time. These events are By the time the piston reaches TDC , combustion is already (a) intake, (b) compression, (c) ignition and power, and (d) in progress.

  • Page 11: Maintenance Schedule

    SECTION 1: GENERAL INFORMATION SECTION CONTENTS NOTE 1: Change oil and filter after first 8 hours of operation and then every 100 hours thereafter. Change sooner when operating under a heavy PAGE load or in a dusty or dirty environment or in high ambient temperature. MAINTENANCE SCHEDULE ...........

  • Page 12: Change Oil

    SECTION 1: GENERAL INFORMATION • During summer months: SAE 30. An acceptable substitute CHANGE OIL FILTER: is SAE 10W-30. After first oil change, synthetic oil is Replace oil filter every 100 hours. Before installing new filter, acceptable. lightly oil filter gasket with fresh clean engine oil. Screw filter •...

  • Page 13: Replace Spark Plugs

    SECTION 1: GENERAL INFORMATION tions are not carefully followed, dirt and dust which should be INTAKE collected in the cleaner, will be drawn into the engine. These SCREEN particles are highly abrasive and will cause the piston rings and cylinder bore to wear quickly. As the rings and cylinder bore become worn, these abrasive particles enter the crankcase and contaminate the oil, forming an abrasive mixture which COOLER...

  • Page 14: Systematic Check

    SECTION 1: GENERAL INFORMATION SYSTEMATIC CHECK: CHECK IGNITION (FOULED PLUG OR OTHER CAUSES): If the engine will not start and the cause of malfunction is To check for a fouled spark plug or a non-functioning cylin- not readily apparent, perform a systematic check in the following der, attach the spark tester (Generac P/N OC5969) between the order: spark plug lead and each spark plug.

  • Page 15: Check Fuel

    SECTION 1: GENERAL INFORMATION If the RPM loss is greater than 75 RPM this indicates that the EXAMPLE: grounded cylinder with the least RPM loss is the weakest of Cyl. #1 Cyl. #2 Diff. the two cylinders. Look to that cylinder for a problem. Eng.

  • Page 16: Equipment Affecting Engine Operation

    SECTION 1: GENERAL INFORMATION EQUIPMENT AFFECTING ENGINE OPERATION Frequently, what appears to be a problem with engine oper- ation, such as hard starting, vibration, etc., may be the fault of the equipment powered rather than the engine itself. Listed are the most common effects of equipment problems, and what to look for as the most common cause.

  • Page 17: Section 1: General Information

    Note: Make sure wires are routed over armature mount- ing posts and away from flywheel. GENERAL INFORMATION Generac GTV-990/760 OHVI V-Twin engines use a magneto ignition: an ignition armature with a self-contained transistor module (no moving parts). Two magneto ignition armatures are used, with a flywheel containing a permanent magnet.
  • Page 18 SECTION 2: IGNITION 4. Repeat for second armature. 5. Adjust armature air gap. ADJUST ARMATURE AIR GAP: laminations. 1. Rotate flywheel until magnet is under armature 2. Place thickness gauge, 0.20-.30 mm (.008"-.012") between magnet and armature laminations, Figure 2-3. 3.
  • Page 19 SECTION 2: IGNITION Figure 2-6. Check Flywheel And Crankshaft Figure 2-8. Installing Flywheel And Fan INSTALL FLYWHEEL: ENGINE WIRING HARNESS Note: CLEAN flywheel and crankshaft taper removing all The engine wiring harness consists of a ground wire with a oil, dirt or grease. diode for each armature and a separate wire for the carburetor 1.
  • Page 20 SECTION 2: IGNITION 1. Insert RED test lead into receptacle in meter. ENGINE 2. Insert BLACK test lead into the “COM” receptacle in meter. GROUND HARNESS 3. Rotate selector to (Diode Test) position. 4. Insert RED test lead clip into connector "A" (Figure 2-10). Leave attached for remainder of test.

  • Page 21: Section 3: Carburetion

    SECTION 3: CARBURETION SECTION CONTENTS PAGE CARBURETOR TYPES ............. 3-1 CARBURETOR REMOVAL..........3-1 CLEANING CARBURETOR ..........3-1 CARBURETOR INSTALLATION ........3-2 STATIC GOVERNOR ADJUSTMENT........3-2 FUEL PUMP ..............3-3 CARBURETOR TYPES There are four types of carburetors used on Generac OHVI V-twin engines: 1.
  • Page 22 SECTION 3: CARBURETION CARBURETOR INSTALLATION - VERTICAL SHAFT (Models EVT-04629-0, EVT-04629-1, 04629-2, EVT-04717-0, 04717-1, EVT-04797-0, 04806-0, 04857-0, 04858-0, 04862-0, 04861-0) 1. Slide new carburetor gasket onto the studs. 2. Slide the carburetor onto the studs. 3. Slide new plenum gasket onto the studs. 4.
  • Page 23 SECTION 3: CARBURETION FUEL PUMP The fuel pump supplied with the engines is a pulse pump. It uses crankcase vacuum pulses drawn from the valve cover of cylinder #2 to pump the fuel. It is capable of priming at 12" (30.5 cm) max lift. The pump has a max outlet pressure of 1.5 psi.
  • Page 24 NOTES...

  • Page 25: Section 4: Governor Controls And Governor

    SECTION 4: GOVERNOR CONTROLS AND GOVERNOR SECTION CONTENTS 1. Force gear assembly and governor spool off of governor PAGE shaft. MECHANICAL GOVERNOR ........... 4-1 2. Remove any remaining plastic from the notch in the gov- GOVERNOR ..............4-1 ernor shaft. GOVERNOR ARM ............
  • Page 26 SECTION 4: GOVERNOR CONTROLS AND GOVERNOR 8. Slide the arm in until the thrust washer is tight. 6. Reconnect the ball joint on the swing arm. 9. Slide the lower bushing down and into it’s holder, then install 7. Place the governor lever on the governor arm, with the the upper e-clip.
  • Page 27 SECTION 4: GOVERNOR CONTROLS AND GOVERNOR DYNAMIC GOVERNOR ADJUSTMENT 1. Start engine and allow to warm up for 5 minutes. 2. Move speed control lever to slow speed position and hold throttle lever against idle stop screw. 3. Adjust stop screw to maintain 1200 RPM idle. 4.
  • Page 28 NOTES...

  • Page 29: Section 5: Cylinder Head And Valves

    SECTION 5: CYLINDER HEAD AND VALVES SECTION CONTENTS PAGE GENERAL INFORMATION ..........5-1 REMOVE CYLINDER HEADS..........5-1 Remove Rocker Arms ..........5-2 DISASSEMBLE CYLINDER HEAD........5-2 INSPECT AND REPAIR ............ 5-3 Reface Valves and Seats ..........5-3 ASSEMBLE CYLINDER HEAD .......... 5-4 INSTALL CYLINDER HEAD ..........

  • Page 30: Disassemble Cylinder Head

    SECTION 5: CYLINDER HEAD AND VALVES Note: Mark components so that they may be reassem- bled in their original position. REMOVE ROCKER ARMS: 1. Unlock jam nuts and remove two ball studs and rocker arm assemblies (see Figure 5-3). 2. Remove push rods and identify each. Note: The valve push rods are aluminum.

  • Page 31: Inspect And Repair

    SECTION 5: CYLINDER HEAD AND VALVES INSPECT AND REPAIR REFACE VALVES AND SEATS: 1. Check cylinder head (Figure 5-7). Be sure all gasket mate- 1. Valve seats may be reconditioned using a valve seat cutter. rial is removed from surfaces before checking. Use a gasket If valve seat is wider than dimension shown in Figure 5-9, a scraper if necessary.

  • Page 32: Assemble Cylinder Head

    SECTION 5: CYLINDER HEAD AND VALVES Note: Lightly coat valve stems with oil or Spectra Lube Red before installing valves. Be sure lubricant is not on valve face, seat or end of valve stem. Figure 5-11. Measure Valve Stem Diameter Intake Valve 5.

  • Page 33: Install Cylinder Head

    SECTION 5: CYLINDER HEAD AND VALVES INSTALL CYLINDER HEAD 1. Install cylinder head with new gasket. 2. Torque head bolts in sequence shown to 29.9 Nm (22 ft. lbs.) (Figure 5-16). 3. Insert push rods into recess in tappets. Figure 5-18. Install Valve Covers REASSEMBLE 1.

  • Page 34: Static Governor Adjustment

    SECTION 5: CYLINDER HEAD AND VALVES 6. Install rotating screen. STATIC GOVERNOR ADJUSTMENT 1. With governor lever clinching screw loose, push on gov- a. Torque screws to 1.9 Nm (17 in. lbs). ernor lever until throttle is wide open. Do not bend governor 7.

  • Page 35: Section 6: Electric Starter

    SECTION 6: ELECTRIC STARTER SECTION CONTENTS ENGINE CRANKS SLOWLY: PAGE a. Additional load affecting performance (see note above). GENERAL INFORMATION..........6-1 b. Discharged battery. TROUBLESHOOTING ............6-1 TEST EQUIPMENT ............6-1 c. Faulty electrical connection (battery circuit). TEST STARTER MOTOR ..........6-2 d.
  • Page 36 SECTION 6: ELECTRIC STARTER Figure 6-2. Digital Multimeter TEST STARTER MOTOR TESTING STARTER SOLENOID: The solenoid is a normally open, electrically activated switch. With the keyswitch in the “START” position, the switch closes, allowing battery current to flow to the starter motor and crank Figure 6-3.
  • Page 37 SECTION 6: ELECTRIC STARTER USE A TEMPERATURE COMPENSATED HYDROMETER CHECK EACH CELL AFTER CHARGING Figure 6-4. Typical Battery INSTALLATION: 1. Before installing battery, connect all equipment to be operated. 2. Place battery in holder with flat base. Tighten holder down evenly until snug.
  • Page 38 SECTION 6: ELECTRIC STARTER OPTIONAL WIRE HARNESS Engines supplied with a wire harness have a Packard #2973422 five terminal female plug on the harness. • Terminal 1 has a brown wire coming from it and is used to signal low oil pressure. When low oil pressure is detected, Terminal 1 becomes a ground.
  • Page 39 SECTION 6: ELECTRIC STARTER Figure 6-8. Figure 6-9. SUPPLIED BY CUSTOMER BLACK TO KILL IGNITION SUPPLIED BY CUSTOMER SUPPLIED BY CUSTOMER BATTERY SUPPLY 12V TO OPTIONAL HIGH TEMP. SWITCH CRANK ENGINE SOLENOID CONNECT TO IGNITION KILL WIRE TO KILL IGNITION ON HIGH TEMPERATURE. CONNECT TO GROUND SIDE OF A LIGHT OPTIONAL CHARGING SYSTEM OR BUZZER TO GROUND THE CIRCUIT...
  • Page 40 NOTES...

  • Page 41: Section 7: Alternators

    SECTION 7: ALTERNATORS SECTION CONTENTS 4. Attach RED and BLACK test lead probes to AC output ter- PAGE minals (white wires), as shown in Figure. 7-1. (Meter test 20 AMP REGULATED ALTERNATOR ....... 7-1 clip leads may be attached to either AC output terminal.) Alternator Output Test ..........
  • Page 42 SECTION 7: ALTERNATORS TESTING REGULATOR-RECTIFIER: 1. Using a digital multimeter, test the battery voltage while the engine is NOT running. 2. With the charging system properly connected, start the engine. 3. Bring the engine up to normal operating speed and test the battery voltage again.

  • Page 43: Section 8: Lubrication System

    PROTECTION SYSTEMS CHECKING THE ENGINE OIL LEVEL The oil capacity of the GTV-990/760 OHVI engine is approx- LOW OIL PRESSURE SWITCH: imately 2 quarts. To check the engine oil level, proceed as The engine is equipped with a low oil pressure sensor that...
  • Page 44 SECTION 8: LUBRICATION SYSTEM Any attempt to crank or start the engine before it has been properly serviced with the recommended oil may result in an engine failure. OIL CHANGE PROCEDURE: Your engine is equipped with an oil filter. Change the oil and FILL / CHECK filter after the first eight (8) hours of operation.
  • Page 45 SECTION 8: LUBRICATION SYSTEM 3. When changing the oil filter, use the following instructions: OIL COOLER: Some engines are equipped with an oil cooler. The oil cooler A) Locate oil filter (Figure 8-4). is mounted on the blower housing. Forced air from the flywheel B) Place a suitable container beneath the oil filter and turn fan flows through the oil cooler fins dissipating heat from the the filter counterclockwise to remove the filter.
  • Page 46 NOTES...

  • Page 47: Section 9: Engine Disassembly

    SECTION 9: ENGINE DISASSEMBLY SECTION CONTENTS PAGE ENGINE DISASSEMBLY ..........9-1 ENGINE DISASSEMBLY Drain oil, remove oil filter and remove engine from equip- ment. Remove spark plugs. Remove flywheel, disconnect stop switch wires at armatures and remove armatures (see Section 2).
  • Page 48 SECTION 9: ENGINE DISASSEMBLY 3. Rotate crankshaft and camshaft until timing marks align 5. Repeat for remaining cylinder. and remove camshaft (Figure 9-3). 6. Remove crankshaft (Figure 9-5). Note: If necessary, place the engine flywheel side down to prevent tappets from catching on the camshaft. a.

  • Page 49: Section 10: Cylinder And Crankcase Cover

    SECTION 10: CYLINDER & CRANKCASE COVER SECTION CONTENTS NOTE: If cylinder bores are within specification and show PAGE no signs of scoring or other damage, new piston rings may be installed providing the cylinder bores are recon- CHECK CRANKCASE............ 10-1 ditioned using a rigid hone with finishing stones, to Resizing ..............

  • Page 50: Cleaning

    SECTION 10: CYLINDER & CRANKCASE COVER It is recommended that the cylinder bores be reconditioned with hot running water. Repeat washing and rinsing until all traces to restore the cross hatch when new piston rings are to be of honing grit are gone. installed in a cylinder that is within specification.

  • Page 51: Install Mag Bearing

    SECTION 10: CYLINDER & CRANKCASE COVER CHECK PTO BEARING The PTO bearing must be replaced if it is damaged or if it measures larger than 42.25mm (1.663”) in diameter (see Figure 10-8). The diameter of the crankshaft may also make it necessary to replace the bearing.

  • Page 52: Install Pto Oil Seal

    SECTION 10: CYLINDER & CRANKCASE COVER INSTALL PTO OIL SEAL: TELESCOPING Install a new PTO oil seal and press it in until it is 1.5mm (1/16”) GAUGE below the mounting surface. CHECK CAMSHAFT BEARINGS Use a telescoping gauge and caliper to check camshaft bear- ings.
  • Page 53 SECTION 10: CYLINDER & CRANKCASE COVER 216mm [8.504"] 16.5mm [0.65"] 183.5mm [7.224"] 10.5mm [0.413"] 17mm [0.67"] Ø12mm [0.473"] TYP 254mm [10.0"] MATERIAL: WOOD 25.4mm [1"] x 216mm [8.5"] x 254mm [10.0"] CLAMP THIS END IN VISE Figure 10-12. Honing Fixture 10-5...
  • Page 54 NOTES...

  • Page 55: Section 11: Crankshaft And Camshaft

    SECTION 11: CRANKSHAFT & CAMSHAFT SECTION CONTENTS CHECK CAMSHAFT: PAGE Inspect gear teeth, lobes and journals for wear and nicks, CHECK CRANKSHAFT ..........11-1 Figure 11-2. Camshaft journal and lobe reject sizes are shown CHECK CAMSHAFT ............ 11-1 below. Replace cam gear if not to specification. CHECK CRANKSHAFT: Camshaft Reject Size Inspect crankshaft threads, keyways and timing gear for...
  • Page 56 NOTES...
  • Page 57 SECTION 12: PISTON, RINGS & CONNECTING ROD INSPECTION & ASSEMBLY SECTION CONTENTS PAGE GENERAL INFORMATION..........12-1 DISASSEMBLE PISTON AND CONNECTING ROD ..12-1 CHECKING PISTON AND RINGS........12-1 CHECKING PISTON PIN AND CONNECTING ROD..12-2 ASSEMBLE PISTON AND CONNECTING ROD ....12-2 ASSEMBLE PISTON RINGS TO PISTON ......
  • Page 58 SECTION 12: PISTON, RINGS & CONNECTING ROD INSPECTION & ASSEMBLY Figure 12-6. Check Piston Pin CONNECTING ROD REJECT SIZE Figure 12-4. Checking Ring End Gap Crankpin Bearing Piston Pin Bearing 39.09mm (1.539") 20.05mm (.7894") CRANKPIN BEARING PISTON PIN BEARING Figure 12-7. Check Rod Bearings Figure 12-5.
  • Page 59 SECTION 12: PISTON, RINGS & CONNECTING ROD INSPECTION & ASSEMBLY ASSEMBLE PISTON RINGS TO PISTON Install piston rings using ring expander when installing center and top compression rings. 1. Install oil ring expander. a. Install lower scraper ring. a. Install upper scraper ring. NOTCH OR 2.
  • Page 60 NOTES...

  • Page 61: Section 13: Engine Assembly

    SECTION 13: ENGINE ASSEMBLY SECTION CONTENTS PAGE INSTALL CRANKSHAFT ..........13-1 INSTALL PISTON AND CONNECTING ROD ....13-1 INSTALL CAMSHAFT ............ 13-2 RING INSTALL OIL PUMP ............13-2 COMPRESSOR INSTALL CRANKCASE COVER ........13-2 INSTALL ALTERNATOR AND IGNITION COILS ....13-3 INSTALL BREATHER ............
  • Page 62 SECTION 13: ENGINE ASSEMBLY INSTALL OIL PUMP 1. Lubricate gerotor and set in place. 2. Install oil pump cover. 3. Torque screws to 12.2 Nm (9 ft. lbs.). Figure 13-4. Torque Connecting Rods 5. Rotate crankshaft two revolutions to check for binding. Rod should also be free to move sideways on crankpin.
  • Page 63 SECTION 13: ENGINE ASSEMBLY a. The allen head crankcase bolt will need to be backed off. 2. Install back plate. 4. Torque screws in sequence shown to 47.5 Nm (35 ft. Ibs.), a. Torque screws to 10 Nm (7.4 ft. lbs.). Figure 13-8.
  • Page 64 SECTION 13: ENGINE ASSEMBLY a. Torque head bolts in sequence shown (Figure 13-13) to 29.9 Nm (22 ft. Ibs.). 3. Insert push rods into recess in tappets. Figure 13-11. Torque Flywheel Nut ADJUST IGNITION COIL AIR GAP 1. Rotate flywheel until magnet is under coil laminations. TORQUE SEQUENCE FOR HEADS: 2.
  • Page 65 SECTION 13: ENGINE ASSEMBLY ADJUST VALVE CLEARANCE 3. Install valve covers with new gaskets, Figure 13-16 1. Set No. 1 cylinder at TDC (Top Dead Center), compression a. Torque bolts to 6.8 Nm (5 ft. lbs.). stroke. a. Adjust rocker arms and check clearance, Figure 13-15. Valve Clearance (cold) IN and EX 0.076mm (.003") b.
  • Page 66 SECTION 13: ENGINE ASSEMBLY 2. Assemble governor lever to governor arm. DO NOT tighten at this time. 3. Install speed adjust assembly. a. Torque screws to 6.0 Nm (53 in. lbs.). 4. Install exhaust. a. Torque screws to 19 Nm (14 ft. lbs.). 5.

  • Page 67: Section 14: Specifications

    SECTION 14: SPECIFICATIONS STANDARD AND REJECT DIMENSIONS DESCRIPTION STANDARD DIMENSION REJECT DIMENSION CYLINDER: Bore 90.00 – 90.025 mm (3.543” – 3.544”) 90.10 mm (3.547”) Out of Round 0.035 mm (.0015”) Main Bearing 38.044 – 38.099 mm (1.498” – 1.5”) 38.25 mm (1.506”) Cam Bearing 20.00 –...
  • Page 68 SECTION 14: SPECIFICATIONS TORQUE SPECIFICATIONS Alternator (to cylinder) 10.0 Nm (7.4 ft. lbs.) Air Cleaner Support Bracket 5.4 Nm (48 in. lbs.) Armature 10.0 Nm (7.4 ft. lbs.) Back Plate 4.5 Nm (40 in. lbs.) Blower Housing 4.5 Nm (40 in. lbs.) Breather 4.5 Nm (40 in.
  • Page 69 NOTES...
  • Page 70 NOTES...
  • Page 71 SECTION XX...
  • Page 72 Printed in U.S.A Copyright © 2001 • Generac ® Power Systems, Inc.

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Gtv-760

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