1985-1995 Polaris ATV and Light Utility Hauler Service Manual, Page 312Get this manual
ENGINES Magnum Engine DisassemblyInspection 4Using the special socket, remove the crankshaft slotted nutNOTE: The slotted nut is left hand thread5Remove cam chain drive sprocket and Woodruff key from crankshaft6Inspect sprocket teeth for wear or damage78Inspect Woodruff key for wearReplace any worn or damaged parts
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 properly9Remove cap bolt, sealing washer, spring, and one way valve from PTO side crankcase
10Inspect free length of spring and check coils for distortion
Inspect for Areas of Tooth Wear or Damage