2004 Yamaha Grizzly 660 Service Manual

The 2004 Yamaha Grizzly 660 is a 4x4 all-terrain vehicle (ATV) featuring a 660cc liquid-cooled, SOHC, 4-stroke engine with 5 valves, Ultramatic automatic transmission with On-Command 2WD/4WD with differential lock, independent front and rear suspension, front and rear hydraulic disc brakes, electric start, and a towing capacity of 850 lbs. This manual provides comprehensive service, maintenance, and repair information for owners and technicians. Below are key sections covering specifications, periodic maintenance, engine service, chassis, electrical, troubleshooting, and safety.

1. General Information & Specifications 2. Periodic Maintenance & Lubrication 3. Engine & Transmission 4. Chassis & Suspension 5. Electrical System 6. Fuel & Exhaust Systems 7. Cooling System 8. Brakes & Wheels 9. Troubleshooting 10. Safety & Environmental Information 11. Wiring Diagrams

General Information & Specifications

Key identification: Model code YFM66FGN, VIN location on frame, engine serial number location.

CategorySpecification
Engine TypeLiquid-cooled, SOHC, 4-stroke, 5-valve single cylinder
Displacement660cc
Bore x Stroke102.0 mm x 80.5 mm
Compression Ratio9.5:1
Starting SystemElectric starter with auxiliary recoil
TransmissionUltramatic automatic V-belt with H/L/N/R gears
Drive SystemOn-Command 2WD/4WD with differential lock
Suspension FrontIndependent double wishbone, 7.1 in travel
Suspension RearSwingarm, 8.7 in travel
Brakes Front/RearHydraulic disc, dual piston
Tires Front/RearAT25 x 8-12 / AT25 x 10-12
Fuel Capacity4.8 gal (18.2 L)
Dry Weight600 lb (272 kg)

Periodic Maintenance & Lubrication

Follow the maintenance schedule for optimal performance and longevity.

  1. Pre-ride inspection: Check tires, brakes, lights, controls, and fluid levels.
  2. Engine oil: Change every 100 hours or 6 months; use Yamalube 4 (10W-30) or equivalent. Capacity: 3.2 qt (3.0 L) with filter change.
  3. Oil filter: Replace with every oil change.
  4. Air filter: Clean every 20 hours; replace if damaged. Use foam air filter oil.
  5. Spark plug: NGK CR8E; gap 0.028-0.031 in (0.7-0.8 mm). Inspect/clean every 100 hours.
  6. Drive belt: Inspect every 200 hours for wear/cracks; replace if necessary.
  7. Front & rear differential oil: Change every 200 hours; use SAE 80 API GL-5 Hypoid gear oil. Capacity: Front 0.32 qt (0.3 L), Rear 0.53 qt (0.5 L).
  8. Brake fluid: Check level; replace every 2 years with DOT 4.
  9. Coolant: Change every 2 years; use ethylene glycol antifreeze for aluminum engines. Capacity: 2.01 qt (1.9 L).
  10. Grease points: Lubricate suspension pivots, steering stem bearings every 100 hours.

WARNING! Always perform maintenance with engine off and cool. Support ATV securely on level ground.

Engine & Transmission

Service procedures for engine removal, disassembly, inspection, and reassembly.

  1. Engine removal: Disconnect battery, drain coolant/oil, remove exhaust, carburetor, electrical connections, and mounting bolts.
  2. Cylinder head: Check for warpage (limit 0.002 in / 0.05 mm). Valve clearance (cold): IN 0.004-0.006 in (0.10-0.15 mm), EX 0.008-0.010 in (0.20-0.25 mm).
  3. Cylinder & piston: Inspect cylinder for scoring; standard bore 102.000-102.010 mm. Piston clearance: 0.0024-0.0031 in (0.060-0.080 mm).
  4. Crankshaft & connecting rod: Check runout (limit 0.002 in / 0.05 mm).
  5. Ultramatic transmission: Inspect drive belt width (wear limit 1.18 in / 30 mm). Check sheave faces for wear.
  6. Clutch service: Clean primary/secondary clutch sheaves; inspect rollers and springs.
  7. 4WD system: Test engagement; inspect differential lock mechanism and front drive shaft.

Torque Specifications (selected): Cylinder head bolts: 33 ft-lb (45 Nm) in sequence. Spark plug: 13 ft-lb (18 Nm). Oil drain plug: 20 ft-lb (27 Nm).

Chassis & Suspension

Frame, suspension, and steering service.

  1. Frame inspection: Check for cracks, especially at welds and stress points.
  2. Front suspension: Remove A-arms; inspect bushings and ball joints for play. Shock absorber: Check for leaks; rebuild if necessary.
  3. Rear suspension: Inspect swingarm pivot bearings and shock linkage. Grease regularly.
  4. Steering system: Check handlebar for bends; inspect tie rods and ends. Adjust toe-in: 0-10 mm (0-0.4 in).
  5. Wheel alignment: Adjust camber if possible; ensure wheels run true.

Tip: Use a torque wrench for all chassis fasteners. Refer to specific torque values in manual.

Electrical System

Battery, charging, starting, and lighting systems.

ComponentSpecification/Test
BatteryYTZ7S (12V, 6Ah). Charging voltage: 14.1-14.9V @ 5000 rpm.
Stator coil resistance0.36-0.48 Ω (20°C/68°F) between terminals.
Regulator/RectifierCheck diode continuity.
Starter motorBrush length limit: 0.24 in (6.0 mm).
CDI UnitDiagnose with Yamaha diagnostic tool.
Headlight12V 30/30W (halogen).
FusesMain 30A, Headlight 15A, Signal 10A.

CAUTION! Disconnect battery negative terminal before electrical service to prevent shorts.

Fuel & Exhaust Systems

Carburetor service and exhaust system inspection.

  1. Carburetor: Mikuni BSR40. Pilot screw initial setting: 2-1/4 turns out. Float height: 0.59-0.67 in (15-17 mm). Clean jets and passages.
  2. Fuel pump: Test flow rate; replace if defective.
  3. Throttle cable: Adjust free play: 0.12-0.20 in (3-5 mm).
  4. Exhaust system: Check for leaks at header and muffler connections. Inspect heat shield.
  5. Fuel tank: Remove and clean if contaminated.

WARNING! Work in well-ventilated area. No smoking or open flames near fuel system.

Cooling System

Maintain proper engine operating temperature.

  1. Coolant drain & refill: Use mixture of 50% ethylene glycol antifreeze and 50% distilled water.
  2. Radiator: Inspect for leaks and damage; clean fins of debris.
  3. Thermostat: Opens at 176-183°F (80-84°C). Test in hot water.
  4. Water pump: Check for coolant leakage at weep hole; inspect impeller.
  5. Hoses & clamps: Inspect for cracks and secure connections.

CAUTION! Never open radiator cap when engine is hot. Allow to cool completely.

Brakes & Wheels

Hydraulic disc brake service and wheel maintenance.

  1. Brake pads: Replace if thickness is less than 0.06 in (1.5 mm).
  2. Brake discs: Check for warpage (limit 0.006 in / 0.15 mm) and thickness (min 0.157 in / 4.0 mm front, 0.197 in / 5.0 mm rear).
  3. Brake fluid replacement: Bleed system to remove air. Use DOT 4 fluid only.
  4. Parking brake: Adjust cable at lever.
  5. Wheels & tires: Check for damage and proper inflation (Front: 3.9 psi / 27 kPa, Rear: 3.4 psi / 24 kPa for standard terrain).
  6. Wheel bearings: Inspect for play or roughness; repack or replace.

Tip: Avoid getting grease or oil on brake pads or discs.

Troubleshooting

SymptomPossible CauseCorrective Action
Engine does not startWeak battery, faulty spark plug, clogged fuel system, bad CDICheck battery voltage, spark, fuel flow, compression.
Engine starts but diesDirty carburetor, faulty fuel pump, vacuum leakClean carburetor, test fuel pump, check intake manifold.
Poor performance/loss of powerClogged air filter, restricted exhaust, worn drive beltService air filter, check exhaust, inspect belt.
OverheatingLow coolant, clogged radiator, faulty thermostatCheck coolant level, clean radiator, test thermostat.
4WD not engagingFaulty switch, actuator, damaged front differentialTest switch/actuator power, inspect differential.
Brakes dragging or weakContaminated pads, air in lines, worn master cylinderReplace pads, bleed brakes, rebuild master cylinder.
Electrical failure (no lights)Blown fuse, bad ground connection, faulty switchCheck fuses, clean grounds, test switch continuity.
Unusual transmission noiseWorn drive belt, damaged clutch sheaves, low oilInspect belt and clutches, check transmission oil level.

Safety & Environmental Information

Safety First: Always wear helmet, eye protection, gloves, and boots. Never operate under influence of drugs/alcohol. Complete training course. Avoid paved surfaces. Be aware of terrain and weather.

Environmental: Dispose of used oil, coolant, batteries, and filters at designated recycling centers. Do not dump into drains or soil.

Service Notes: Use genuine Yamaha parts or equivalents meeting specifications. Keep work area clean and organized.

Wiring Diagrams

Refer to fold-out section at back of manual for complete color-coded wiring diagrams covering:

Note: Use a multimeter for continuity and voltage tests. Diagram key identifies wire colors and connector codes.

For Technical Support: Contact authorized Yamaha dealer or Yamaha Motor Corporation, U.S.A. Customer Relations at 1-800-962-7926.

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