Yamaha Big Bear 400 4WD IRS (YFM40FBW) 2006–2012 ATV Service Manual (P/N LIT-11616-20-45)

Yamaha’s YFM40FBW service manual covers maintenance, diagnosis, and repair of the Big Bear 400 4WD IRS, identified by model codes 4S11 and 4S14. This is the first edition, November 2006, carrying P/N LIT-11616-20-45 and 4S1-F8197-10.

Searchable PDF and Wiring Detail

Text search, bookmarks and diagrams: Searchable text and section bookmarks support navigation, although several chapter bookmarks open the contents pages. Small component references, connector labels, and wire-color codes in the wiring diagrams are readable when enlarged.

The download contains one printable, English-language PDF with 391 pages: 370 chapter pages, 17 opening pages including the front cover and one blank, two wiring-reference pages, one additional blank page, and the rear cover.

Engine, Shaft-Drive and Electrical Service

The selected coverage below highlights major workshop tasks. Other topics include speed-limiter adjustment and spark-arrester cleaning.

• Engine repair: Engine removal, cylinder-head and piston service, camshaft and valve inspection, plus oil-pump and balancer-gear inspection and assembly.

• Clutch and transmission: Primary and secondary clutch inspection, transmission disassembly and reassembly, and checks of the shift shaft, shift forks, and shift drum.

• Mikuni BSR33 carburetor: Step-by-step disassembly, cleaning, inspection, and reassembly procedures, with float-height checks and fuel-level adjustment.

• Shaft drive: Front and rear constant velocity joint service, differential gear-case inspection, final-drive repair, and middle, differential, and final gear-lash adjustment.

• Brake service: Front pad replacement, master-cylinder and caliper rebuilding, hydraulic bleeding, and inspection of the rear wet-brake friction plates, springs, and pressure plate.

• Steering and suspension: Steering-knuckle and ball-joint replacement, tie-rod-end inspection, toe-in adjustment, and service of the suspension arms, rear knuckles, and stabilizer.

• Electrical troubleshooting: Ignition, starting, charging, oil-cooler fan, and 2WD/4WD circuit diagrams, supported by troubleshooting flowcharts, switch continuity tables, and electrical test specifications.

Yamaha wrote this manual primarily for dealers and qualified mechanics, assuming basic mechanical knowledge and familiarity with vehicle repair procedures.

Engine Inspection and Reassembly

Beyond routine checks, the engine chapter covers crankcase separation, crankshaft inspection, recoil-starter rebuilding, and AC magneto rotor removal. Camshaft timing illustrations, engine lubrication diagrams, and crankcase and cylinder-head tightening sequence views support reassembly.

Factory wear limits and exploded assembly views let a mechanic compare dismantled parts with service criteria and check how the assemblies fit together. Periodic maintenance charts connect those repair sections with scheduled checks and adjustments.

Differential and Final-Drive Work

Gear-lash measurement drawings accompany shim-selection procedures for the middle gears, front differential, and rear final drive. Rear final-drive coverage also includes pinion-bearing installation and ring-gear thrust-clearance measurement.

Differential assembly limit: The factory-assembled internal differential unit must remain assembled; the manual warns that dismantling it causes malfunction. The surrounding gear case, actuator, seals, bearings, and adjustment procedures are treated separately.

Lubricant information distinguishes the front differential from the rear final gear case containing the wet brake. For the rear case, Yamaha identifies the recommended friction-modified oil and a permitted substitute, noting that the substitute may produce brake noise.

Brake, Steering and Suspension Details

The chassis sections provide step-by-step procedures for hydraulic brake bleeding, steering toe-in adjustment, and ball-joint replacement. Suspension data includes travel and spring specifications; shock-absorber procedures cover inspection, preload adjustment, and assembly replacement rather than internal rebuilding.

Working on the 4WD IRS system involves high-torque components and pressurized brake fluid. Follow the manual’s safety precautions and consult a qualified ATV technician when needed.

Electrical Fault Isolation

The starting-circuit explanation distinguishes gear-position and rear-brake-switch interlocks from starter-motor faults, helping narrow a no-crank diagnosis before replacement parts are selected. Starter-motor disassembly includes commutator, armature, brush, and spring checks.

Stator/pickup-coil and CDI troubleshooting leads to replacement when the relevant checks fail. Oil-cooler fan diagnosis covers the motor, relay, circuit breaker, temperature sensor, and control unit; separate carburetor-warming tests address the heater and thermo switch.

Cable-routing diagrams and the complete wiring diagram with its component legend and color-code key support harness tracing.

Model-Specific Repair Pitfalls

The differential-motor test warns against using vehicle-battery voltage, which risks motor damage. The middle driven pinion gear bearing retainer has left-hand threads, making its thread direction important to avoiding retainer damage.

A Preview of Valve and Routine-Service Specifications

Valve adjustment: Cold clearances are listed at 0.06–0.10 mm for the intake and 0.16–0.20 mm for the exhaust, alongside measurement views and adjustment instructions.

Routine service: The periodic engine-oil change quantity is 2.90 L, distinct from the filter-change and total-capacity entries. Ignition service data specifies a 0.6–0.7 mm gap for the NGK DR8EA spark plug.