2001 Polaris Sportsman 400-500 DUSE and H.O. Service Manual, Page 134Get this manual
PISTON INSTALLATION
1Clean the gasket surfaces on the cylinder and crankcaseRemove all traces of old gasket material2Make sure the cylinder mounting bolt holes are clean and free of debris3Install new circlip on one side of the piston with the end gap facing up or down, and tang outwardCAUTION: Circlips become deformed during the removal processDo not re-use old circlipsDo not compress the new clip more than necessary upon installation to prevent loss of radial tensionSevere engine damage may result if circlips are re-used or deformed during installation4Apply clean engine oil to the piston rings, ring lands, piston pin bore, piston pin, and piston skirtLubricate the connecting rod (both ends), balancer drive gear, and crankshaft main bearing area5Install the piston on the connecting rod with the arrow ormark facing the magneto (RH) end of the crankshaftThe piston pin should be push fit in the piston6Install the other circlip with the gap facing up or down and tang outward(See Caution with step above)Push the piston pin in both directions to make sure the clips are properly seated in the grooveor