setting the timing in yamaha moto 4

[aftrmath99]

this may sound stupid but can someone give me step by step instructions on how to set the timing in a yamaha moto 4  motor  we took it apart and dont really know how to reset  the timing  we didnt pull the cylinder  just the top and did not pull the piston completely out we did remove the timing chain and thats what we are havin trouble with  how to replace it  we pulled the exhaust and cleaned the valves so now im sure we are screwed lol i put the piston at top dead center but im not sure about the valves and how to set them when we put it back together we didnt have any compresion kinda lost  daaaaa