2008 Polaris Sportsman 500 EFI/X2/Touring/500 H.O. Service Manual, Page 291Get this manual
TRANSMISSION 6Inspect the shift drum for any damage or wearInspect the splines of the shift drumReplace the O-rings on the end of the shift drum and lubricate them before assembly9With the gearcase on it's side, hold the gear cluster assembly and output assembly togetherCarefully install each shaft into their respective recess in the gearcaseStretch 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)Silent Chain Length: 3.0904" (7.8496 cm)