Originally Posted by james chevy
i have sbc 350 when i adjust valves 0 lash then half turn doesnt wont to run if i back off till rocker arms are loose runs ok why is that.its like it has solid lifters but doesnt
It may be the method you're using to find zero lash. If you're twisting the pushrods, that could be your problem because only an experienced builder will have the experience to "feel" when the play goes away.
A more accurate method, particularly for someone who does not build motors day in and day out, is to jiggle the pushrod up and down and slowly tighten the nut. Have your buddy hold the rocker tightly down against the valve stem while you jiggle the pushrod up and down and tighten the nut. When you can't jiggle it any longer, you are at zero. Of course, you also need to be on the heel of the cam lobe to do this. Turn the crank until you get max valve open, then turn the crank one full turn. That'll put the tappet on the heel of the lobe.
If, as in your case, you already have the motor running and are past the building stage, go to the boneyard and get a couple of sacrificial valve covers. Cut the tops out of them and bolt them on. Now, you can run the motor and adjust the valves the proper way without gettin' oil all over everything. Back 'em off until they clatter, then tighten to what ever you think is right based on info from the cam grinder/tappet mfg.