2001 Polaris Sportsman 400-500 DUSE and H.O. Service Manual, Page 128Get this manual
PUMP SHAFT END PLAY ADJUSTMENT
1Make sure the pump shaft bearing is firmly seated in the Magneto side crankcase2Measure the distance from the magneto crankcase mating surface to the bearing using dial caliper and straight edgeSubtract the thickness of the straightedge and record
3Install the gear on the oil pump and measure the width of the pump and gearSubtract this measurement from the measurement recorded in Step 24Subtract the thickness of the existing shim from the result of Step to determine if different shim is needed