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

• Official 391-page Yamaha OEM publication (P/N LIT-11616-20-45) documenting the 4S11 and 4S14 series chassis
• Contains 56 exploded-view diagrams, 16 comprehensive wiring schematics, and 3 detailed lubrication charts
• Fully indexed, searchable PDF formatted for high-resolution standard letter and A4 shop printing

Documented Maintenance Scope

The factory documentation segments critical system checks across nine distinct chapters. It delivers precise baseline metrics for engine management, mapping out exact tolerances for top-end valve clearance adjustments, camshaft inspections, and crankcase internals like the oil pump and balancer gear. Chassis coverage breaks down steering geometry and suspension travel specs. It also isolates the unique wet multiple-disc brake system housed within the final drive. Need to troubleshoot electrical faults? The reference provides complete circuit diagrams detailing the ignition, charging circuits, and the 2WD/4WD selecting mechanisms, alongside factory fuse ratings.

Technical Data Highlights

This reference outlines all fundamental engine parameters for the 387.0 cc powerplant, maintaining an 8.60:1 compression ratio for standard rebuilding. Cylinder head assembly is mapped through a multi-stage bolt torque sequence specific to the 4S1 builds. Factory clearances are strict: intake valves require 0.06–0.10 mm, while exhaust valves need 0.16–0.20 mm. Fluid capacities are clearly defined for the shop floor. A periodic oil change takes 2.90 liters, and the differential gear case calls for 0.23 liters of specialized friction-modified lubricant. Spark plug gaps are set at 0.6–0.7 mm for the standard NGK DR8EA.

Working on the 4WD IRS system involves high-torque components and pressurized fluids. Always verify these factory-spec values and consult a certified ATV technician before initiating heavy maintenance to ensure operational safety and equipment integrity.