Both of you guys are wrong or only partly right and he's asking for a BURNED VALVE, not a bent pushrod or any of that.
Do not do any adjusting with the engine running as it's inaccurate and will result in a burned valve if you don't know what you're doing.
Do not use a feeler gauge to set your valve lash. That is done with SOLID LIFTER CAMS ONLY UNLESS YOU USE RHODES LIFTERS.
With a normal hydraulic cam, you have to make sure that the cam is on the base circle (no lift). That means you need to either have it on top dead center of the compression stroke of the cylinder or have the intake valve just starting to open or the exhaust valve just starting to close. I prefer the latter method as it's more accurate. Then, you spin the pushrods in your hand and when you feel a slight resistance, tighten them 1/4-1/2 turn more.
That's the correct way, that's how I set mine, and I have no burned valves, bent pushrods, or wiped cam as a result and my lifters don't clack. BTW, I have a Comp Xtreme 4x4 that was installed on an engine stand, making the job much easier.
Tim
'84 Chevy K10, lifted, loud, fast, and 3/4 ton axles