2004 John Deer Buck Utility ATV 500, 500EX and 500EXT Service Manual, Page 39Get this manual
Install genuine partsGo to next stepPoor oil quality? Use high quality oilGo to next stepLeaks at air intake manifold (engine gets too lean)? Retighten screws or replace air intake manifoldGo to next stepContamination (like sand) through engine intake? Replace defective part(s) and use new air filterGo to next stepMelted andor perforated piston dome; melted section at ring end gapSpark plug heat range is too low? Install recommended spark plugGo to next stepCoolant less than recommended level (engine gets too hot)? Repair cooling circuit andor refill with recommended liquidGo to next stepPoor quality andor wrong fuel? Clean from contamination and use appropriate fuelGo to next stepCracked or broken pistonCracked or broken piston due to excessive pistoncylinder clearance or engine overreving? Replace pistonCheck pistoncylinder clearance (refer to "Cylinder and Head")Go to next stepCheck connecting rod, crankshaft, rocker arm rollers movementConnecting rod failure due to lack of oil? Repair and replace defective parts and use high quality oilGo to next stepCrankshaft failure due to lack of oil?