2002–2006 Yamaha Grizzly 660 YFM660 Factory Service Manual (P/N LIT-11616-15-01)

• Model identification: Covers Yamaha YFM660F model codes 5KM1 and 5KM5 in a 404-page PDF; the closing master wiring diagram is labeled YFM660FP.
• Engine repair: Documents engine removal and installation, camshaft timing and decompression-system checks, valve and cylinder-head work, piston inspection, crankcase separation, crankshaft installation, and balancer and oil-pump service.
• Automatic transmission service: Follows primary and secondary sheave removal, inspection, and reassembly; centrifugal clutch repair; V-belt checks; transmission teardown; middle-gear shim selection; and backlash measurement.
• 4WD driveline work: Covers front CV joints and differential gear, gear-motor testing and indexed installation, differential lash adjustment and operation checks, plus the rear CV joint, final drive, pinion-and-ring-gear positioning, and drive-shaft inspection.
• Fuel and cooling systems: Includes Mikuni BSR42 carburetor disassembly, inspection, assembly, and fuel-level adjustment, along with radiator testing, thermostat checks, and water-pump mechanical-seal service.
• Chassis repair: Details brake pads, master cylinders, calipers, hydraulic bleeding, wheel hubs and discs, steering stem, tie rods and knuckles, front arms, rear suspension, and stabilizer inspection.
• Electrical diagnosis: Provides circuit diagrams and fault-isolation procedures for ignition, electric starting, charging, lighting, signaling, fan and cooling controls, and 2WD/4WD selection.

This Yamaha service manual is for readers who need repair procedures and test data rather than an owner's-level maintenance summary. The press work, gear-lash setup, engine teardown, and circuit testing make it best suited to professional technicians and experienced owners who already have the specified pullers, holders, gauges, and electrical test equipment.

Machine-Specific Systems and Service Work

The opening feature section explains how the selectable front differential transmits power in 2WD, 4WD, and 4WD Diff-Lock, including the gear motor, drive clutch, standby condition, and indicator-light behavior. It also illustrates the park-equipped shift mechanism and the compact three-shaft transmission, where reverse is driven by a chain rather than the forward gear path.

Periodic service coverage includes valve-clearance and timing-chain adjustment, ignition-timing and compression checks, engine and gear-oil service, cooling-system maintenance, hydraulic brake bleeding, select-lever cable and toe-in adjustment, V-belt inspection, and battery, fuse, and headlight checks. Major repair chapters then carry those systems through removal, disassembly, inspection, assembly, installation, and final adjustment where applicable.

Diagrams, Diagnostics, and Specifications

Each major removal or disassembly section starts with an exploded view and job-order chart, followed by the related inspection and assembly notes. The specification material supplies component torque data, fluid capacities and approved lubricants, wear limits, clearances, gear-lash and shim data, carburetor settings, and electrical test values.

Named reference graphics include the coolant-flow and oil-flow diagrams, cable-routing plates, ignition-system circuit diagram, 2WD/4WD selecting-system circuit diagram, and full YFM660FP wiring diagram. Electrical chapters use component tests and fault-isolation charts instead of providing schematics alone. The final troubleshooting section separates starting and hard-starting complaints into fuel, electrical, and compression causes, then addresses running faults, driveline noise, shifting and clutch problems, overheating, braking, suspension and handling complaints, and lighting failures.

Special Tools and Repair Cautions

The special-tool section distinguishes U.S./Canadian numbers from the corresponding 90890-series numbers. Examples include the crankcase separating tool YU-01135-A / 90890-01135 and gear-lash measurement tool YM-01467 / 90890-01467. The manual also identifies the sheave spring compressor YM-04134 / 90890-04134 and electrical pocket tester YU-03112 / 90890-03112, with the job each tool supports.

Several driveline cautions are specific enough to matter before repair work begins. Pressing directly on the middle driven-shaft end can damage its threads, and its bearing retainer uses left-hand threads. During front differential gear-motor installation, disturbing the indexed shift-fork slider can leave the indicator out of sync and prevent 2WD or differential lock from engaging.

Brake, wheel, and suspension procedures require the ATV to be securely supported. Hydraulic brake repair also calls for the specified fluid, clean internal components, correct hose routing, and complete bleeding before the machine is returned to service.