1999-2002 TRX400EX Fourtrax Service Manual, Page 115Get this manual
CYLINDERPISTON Check the top of the cylinder for warpage with straight edge and feeler gauge across the studs and bolt holes as shownSERVICE LIMIT 0.10 mm (0.004 in)
PISTONPISTON RING Inspectthe piston rings for movement by rotating the ringsThe rings should be able to move in their grooves without catchingPush the ring untilthe outer surface of the piston ring is nearly flush with the piston and measure the ringto-ring groove clearanceSERVICE LIMITS: Top: 0.14 mm (0.006 in) Second: 0.12 mm (0.005 in)
Insert each piston ring into the bottom ofthe cylinder squarely using the pistonMeasurethe ring end gapSERVICE LIMITS Top: 0.50 mm (0.020inl Second: 0.65 mm (0.026 in) Oil (side rail): 0.9 mm (0.04in)