i have a 1978 W100 4X4 with a 440. i can hear a valve clacking around and its loud. its annoying too. i was wondering how bad it is to drive around with that going on. this truck isnt my everyday ride so its ok if it takes time to take care of it. i just need to know if it is going to kill the truck or what. i plan on rebuilding the motor soon enough but for know i like to drive it around on the weekends. any help i can get is welcome.