2003 Yamaha Grizzly 660 Service Manual

The 2003 Yamaha Grizzly 660 is a four-wheel drive all-terrain vehicle (ATV) featuring a 660cc liquid-cooled, SOHC, 4-stroke engine, Ultramatic automatic transmission with engine braking, On-Command 2WD/4WD with differential lock, independent double wishbone front suspension, and a swingarm rear suspension. This service manual provides comprehensive information for maintenance, troubleshooting, and repair procedures. Below are key sections covering specifications, periodic maintenance, engine service, chassis, electrical system, and troubleshooting.

1. General Information & Specifications 2. Periodic Maintenance & Lubrication 3. Fuel System & Throttle 4. Engine & Transmission 5. Chassis & Suspension 6. Electrical System 7. Brake System 8. Drive System 9. Troubleshooting 10. Wiring Diagrams

General Information & Specifications

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

Category	Specification
Engine Type	660cc, liquid-cooled, SOHC, 4-stroke, single cylinder
Bore x Stroke	102.0 mm x 80.5 mm
Compression Ratio	9.2:1
Fuel System	Mikuni BSR42 carburetor
Starting System	Electric start with auxiliary recoil
Transmission	Ultramatic automatic V-belt with H, L, N, R, Park
Drive System	On-Command 2WD/4WD with differential lock
Suspension Front	Independent double wishbone, 6.7 in travel
Suspension Rear	Swingarm, 7.1 in travel
Brakes Front/Rear	Dual hydraulic disc / Sealed wet multi-disc
Tires	AT25 x 8-12 front, AT25 x 10-12 rear
Fuel Capacity	4.8 US gal (18.2 L)
Dry Weight	600 lb (272 kg)

Periodic Maintenance & Lubrication

Follow scheduled maintenance intervals for optimal performance and safety.

Pre-ride inspection: Check tires, brakes, lights, controls, fluid levels.
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.
Oil filter: Replace with every oil change.
Air filter: Clean every 20 hours; replace if damaged. Use foam air filter oil.
Spark plug: NGK DR8EA; gap 0.028-0.031 in (0.7-0.8 mm). Inspect/clean every 100 hours.
Drive belt: Inspect every 100 hours for wear/cracks; replace if necessary.
Front/Rear differential oil: Change every 200 hours; use SAE 80 API GL-5 Hypoid gear oil. Capacity: 0.42 qt (0.4 L) each.
Brake fluid: Check level; replace every 2 years. Use DOT 4.
Grease points: Lubricate suspension pivots, steering stem bearings every 100 hours.

WARNING! Always support ATV securely on level ground before maintenance. Allow engine to cool before servicing.

Fuel System & Throttle

Mikuni BSR42 carburetor with throttle position sensor (TPS).

Carburetor adjustment: Idle speed: 1400 ± 100 rpm. Pilot screw initial setting: 2-1/4 turns out.
Fuel valve: Three positions: ON, RES, OFF. Use RES when main tank is low.
Fuel filter: Inline filter; replace if clogged.
Throttle cable free play: Adjust to 0.24-0.35 in (6-9 mm) at throttle lever.
Choke: Manual choke lever on carburetor for cold starts.

CAUTION! Work in well-ventilated area; no sparks or flames. Fuel is highly flammable.

Engine & Transmission

Engine removal, disassembly, inspection, and reassembly procedures.

Cylinder head: Torque sequence: 37 ft-lb (50 Nm) in crisscross pattern.
Valve clearance: Check cold. Intake: 0.004-0.006 in (0.10-0.15 mm). Exhaust: 0.008-0.010 in (0.20-0.25 mm).
Piston & rings: Standard piston diameter: 3.937 in (100.0 mm). Ring end gap: Top 0.012-0.020 in (0.30-0.50 mm), Second 0.012-0.018 in (0.30-0.45 mm).
Crankshaft: Connecting rod side clearance: 0.008-0.017 in (0.20-0.45 mm).
Clutch: Primary and secondary sheave inspection; belt width specification: 1.18 in (30 mm) min.
Transmission case: Oil capacity: 0.95 qt (0.9 L) Yamaha Hypoid gear oil SAE 80.

Tip: Use a service stand to support the ATV frame during engine removal.

Chassis & Suspension

Frame, suspension components, steering, and wheels.

Front suspension: Remove wheel, shock absorber, upper/lower A-arms. Inspect bushings and ball joints.
Rear suspension: Swingarm removal; check pivot bearings for wear.
Steering stem: Adjust bearing preload; torque steering stem nut: 65 ft-lb (88 Nm).
Wheel alignment (Toe-in): Adjust tie rods to set 0-10 mm toe-in.
Wheel bearings: Inspect for smooth rotation; replace if rough or noisy.
Tire pressure: Standard: 3.6 psi (25 kPa) front, 3.6 psi (25 kPa) rear (for standard tires). Adjust for load/terrain.

Electrical System

Battery, charging system, starting system, lighting, and switches.

Component	Specification/Test
Battery	YTZ7S, 12V 6.3Ah. Charging voltage: 14.1-14.9V @ 5000 rpm.
Starter motor	Brush length min: 0.35 in (9.0 mm).
Starter relay	Click test; continuity check.
Alternator	AC magneto output: 50V AC min @ 5000 rpm (lighting coil).
CDI Unit	Resistance tests per manual. No disassembly possible.
Headlight	12V 30/30W (halogen).
Fuses	Main 30A, Headlight 15A, Signal 10A, Ignition 10A.

CAUTION! Disconnect negative battery terminal first when working on electrical system.

Brake System

Hydraulic disc brakes front, sealed wet multi-disc brake rear.

Front brake pads: Replace if thickness is less than 0.12 in (3.0 mm).
Brake disc thickness: Standard: 0.157 in (4.0 mm). Minimum: 0.138 in (3.5 mm).
Brake fluid replacement: Bleed system; use DOT 4 fluid.
Rear brake adjustment: Adjust cable free play at lever: 0.4-0.6 in (10-15 mm).
Parking brake: Adjust cable to hold ATV on a slope.

WARNING! Brake fluid damages paint. Clean spills immediately. Do not reuse old fluid.

Drive System

On-Command 2WD/4WD system, front differential, drive shafts.

4WD operation: Engage/disengage via handlebar switch. Differential lock engaged via separate button (for 4WD only).
Front differential oil: SAE 80 API GL-5, 0.42 qt (0.4 L).
Drive shaft boot inspection: Check for tears/leaks; replace boot if damaged.
Wheel hub engagement: Test for positive engagement in 4WD mode.

Tip: Do not engage differential lock on hard surfaces to avoid drivetrain binding.

Troubleshooting

Symptom	Possible Cause	Corrective Action
Engine does not start	Fuel, spark, compression	Check fuel valve, spark plug, carburetor, compression (142 psi min).
Engine starts but dies	Clogged pilot jet, bad gas	Clean carburetor, drain old fuel, check fuel flow.
Poor performance/loss of power	Clogged air filter, drive belt wear	Clean/replace air filter, inspect drive belt, check exhaust for restrictions.
Overheating	Low coolant, clogged radiator	Check coolant level, inspect radiator fins, check water pump.
4WD not engaging	Faulty switch, actuator, vacuum lines	Check switch operation, actuator motor, vacuum lines for leaks.
Electrical failure (no lights/start)	Blown fuse, bad battery, loose connection	Check main fuse, battery voltage/connections, ground wires.
Abnormal noise from engine	Valve clearance, cam chain tensioner	Adjust valves, check automatic cam chain tensioner.
Brakes dragging or weak	Contaminated pads, air in lines, worn pads	Clean/inspect discs and pads, bleed brake system, replace pads.

Reset ECU: Disconnect battery for 10 minutes to clear fault codes (if applicable).

Service: Refer to authorized Yamaha dealer for complex issues. Yamaha Customer Relations: 1-800-962-7926.

Wiring Diagrams

Complete wiring diagrams for the 2003 Yamaha Grizzly 660 are included in the full service manual. Diagrams cover the main harness, lighting system, starting/charging system, ignition system, and switch connections. Use for tracing circuits, diagnosing electrical faults, and understanding component interconnections.

Note: Always use a multimeter for continuity and voltage tests. Ensure all connections are clean and tight after repairs.