1999-2004 Honda 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 shown-
SERVICE LIMIT 0.10 mm (0.004 in)
PlSTONlPlSTON RING
Inspect the piston rings for movement by rotating the ringsThe rings should be able move in their grooves without catchingPush the ring until the outer surface of the piston ring is nearly flush with the piston and measure the ringto-ring groove clearance