2005 Polaris Sportsman 400/500 Service Manual, Page 230Get this manual
TRANSMISSION 12Inspect the shift drum for any damage or wearInspect the splines of the shift drumReplace the Orings on the end of the shift drum and lubricate them before assemblyC
13Stretch the silent chain on flat surface and measure the length of pitches in minimum of three places on the chainReplace the chain if the measurement is longer than 3.0904" (7.8496 cm)
15With the gearcase on it's side, hold the gear cluster assembly and output assembly togetherCarefully install each shaft into their respective recess in the gearcase