1968 targa 912 rocker arms

i keep breaking the same rocker arm on my car. What can I look at internally that keeps causing it to break? Yes i have ran it hard the first time.crcarrillo2003@yahoo.com...thank you

try not to tourk it to tight example only if spects say tork 55 foot pounds,drop back to 48 foot pounds,rember weare and tear on engine. see you din mention if engine has been re built.