2003 Yamaha YFM400FAR Kodiak Factory Service Manual, Page 204Get this manual
MIDDLE GEAR
4.Check: O-ring Damage ReplaceG Bearings Pittingdamage Replace5.Check: U-joint movement Roughness Replace U-joint
SELECTING THE MIDDLE DRIVE AND DRIVEN GEAR SHIMS When the drive and driven gear, bearing housing assembly andor crankcase are replaced, be sure to adjust the gear shims1.Select: Middle drive gear shim Middle driven gear shim Selection steps: Position middle drive and driven gear by using shims and with their respective thickness calculated from information marked on crankcase, bearing housing and drive gear end1 Shim thickness "A" Shim thickness "B"