lost need help bad

I have a problem for all the Honda gurus I have a 1987 Honda TRX 250 X that I’ve been building I got the engine all back together and found out the exhaust valves was hitting the piston now I don’t know if the engine has been messed with before me but when I did the motor machine shop at the mill the head 2000 so my question is does anybody know what I can do to fix the problem of the valves hitting the head