2005-2009 Honda TRX400EX/TRX400X Service Manual, Page 151Get this manual
CYLINDERPISTON Install the two dowel pins and new gasket
Blow through the oil passage in the cylinder with compressed airCoat new D-ring with oi and insta ll it into the groove in the cy linder bottom
Apply engine oil to the cy linder wall, piston outer surface and piston ringsBe carelu! nor to damage rhe piS ron rings and cvlinder wall