1985-1986 Yamaha YZ490S / YZ490 Service Manual (P/N LIT-11626-05-11)

• Official Yamaha publication P/N LIT-11626-05-11 (First Edition, August 1985) covering the 1985–1986 YZ490S and YZ490 two-stroke competition machines.
• Documents key technical data across 114 pages, including exploded-view mechanical assembly diagrams, electrical system specifications, and critical torque values.
• Contains the original technical specifications and baseline settings used for YZ-series motocross development.

Technical Overview and Engine Walkthrough

The 1985–1986 Yamaha YZ490 owner's and service guide delivers a comprehensive breakdown of the 490 cc motocross platform. It outlines factory specifications essential for accurate restorations and bench work. General information chapters define identification markers, a 24:1 fuel mixing ratio, and long-term storage preparation protocols. Engine sections meticulously document the reed valve system, Y.E.I.S. chamber, and clutch assembly. Mechanics will find precise wear limits for friction plates alongside push rod runout tolerances.

Chassis Data and Specification Highlights

Chassis documentation focuses heavily on the Monocross suspension system. It details rear shock gas pressure settings at 981 kPa (142 psi) and provides the factory baselines for rebound damping adjustments. Steering head torque values are clearly stated at 130 Nm (94 ft-lb) for the stem nut. Cylinder head torque requires 22 Nm (16 ft-lb) applied in a specific crisscross sequence. The manual also breaks down swingarm linkages and sprocket assemblies for accurate part identification. Note that all referenced specifications are intended for informational review prior to service; any hands-on shop work must always rely on proper tooling, a safe environment, and strict adherence to the complete OEM documentation guidelines.