1999-2002 TRX400EX Fourtrax Service Manual, Page 118Get this manual
CYLINDERPISTON NOTE: Make sure that the piston pin clips are seated securelyDo not align the piston pin clip end gap with the piston cutout
CYLINDER INSTALLATION
Clean the gasket surfaces of the cylinder and crankcase thoroughly, being careful not to damage it, and careful not to allow gasket material into the crankcase