2012 Sportsman 400/500 and EFI Tractor Service Manual 9923412, Page 93Get this manual
ENGINE One Way Valve
The one way valve prevents oil from draining out of the oil tank and into the crankcase when the engine is offIt must be clean and have adequate spring pressure in order to seal properly1Remove cap bolt (A), sealing washer (B), spring (C), and one way valve (D) from PTO side crankcase3Tap lightly on balancer gear with brass drift through the hole in the crankcase if necessary, to ensure the balancer shaft stays in the PTO side crankcaseWatch the gap along the crankcase mating surface and separate the crankcase evenlyIt may also be necessary to tap the oil pump shaft lightly to separate the crankcase
CAUTION
Do not strike the oil pump shaft at an angle or the shaft may bend, causing irreparable damageTap only lightly on the pump shaft if necessary4Remove the Mag (RH) crankcase from the PTO case