2012 Sportsman 400/500 and EFI Tractor Service Manual 9923412, Page 325Get this manual
TRANSMISSION Transmission Assembly
1Assemble the reverse shaft assembly and input shaft assembly if previously disassembled (see illustrations)2Inspect the shift drum for any damage or wearInspect the splines of the shift drumReplace the O-ring on the end of the shift drum and lubricate it before assembly
3Stretch 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 the service limit