Okay we replaced the pushrods in my friends 350 but it still makes a tapping noise we checked the compression on the cylinder and it is still good so the valve should be fine. RIght So what could this noise be .

 

Try setting the valve lash.

 

what made you change the pushrods?

and yes, check valve lash.....

solid or hydraulic cam?

 

they are hydralic lifters and we changed the push rods casue the rocker slipped off and casued them to bend.

 

what do you mean by setting the valve lash

 

When you replaced the pushrods how much more of a turn did you give it past zero lash? 1/2 to 1 full turn is where the final adjustment needed to be. That means if your running the engine and cranking each nut down until it the rocker stops ticking from that point you give it 1/2 to 1 full turn extra. Of course you should always back each one off one more time and adjust it the same to make sure. Your friend may need lifters. I assume you found out why the pushrod came off in the first place? Rocker arms dont just slip off unless your running a type that doesent match the head.

 

its always possible you have a bad lifter too ....if or when you set the valve lash it should go away unless you have a bad lifter from the sounds of it ....

 

Try this, pull the valve cover and place the engine on #1 top dead center. You can establish that by having someone crank the engine over (slowly) with the plug out of #1 hole. Put your finger over the hole if you have to, (D/C the ignition wire) when your finger is blown off of the plug hole you're at TDC. You may have to rock the engine back a little to line up the timing mark, but usually it'll be close. Now using a wrench (prefferably) or a remote starter (not so good) crank the engine over until the exhaust valve starts to open, (emphasize STARTS TO OPEN) at that point the intake is valve is on the heel of the cam and can be adjusted. To adjust it you need to loosen the intake rocker so that the hopefully straight pushrod is a little loose. This will allow the hydraulic lifter to expand to it's full length. Now, carefully, while moving the pushrod up and down, tighten the rocker down until there is no more movement in the pushrod. At that point, tighten it down another 1/2 turn. (some people like 3/4). The intake valve is now adjusted. Crank the engine over in the same direction until the intake starts to close (emphasize START TO CLOSE) at this point the exhaust is on the heel of the cam and may be adjusted the same way. You can now go to #8 and so forth down the order,until all of the valves are adjusted. Bolt the covers on and you're done.
The other way to do this is the way SSC describes, start the engine with the valve cover off, (or make a set with holes cut in them so you don't spray oil everywhere) Loosen up each rocker until it clatters and then slowly tighten them down (emphasize SLOWLY) until the rocker shuts up and go another 1/2 turn, (some people like 3/4), or whatever works for you. The second method is faster but sloppier, and certainly not as precise. If you have solid lifters this routine will become second nature. If you happen to over rotate the engine, don't panic, as long as you follow the exhaust/open adjust intake, intake/close adjust exhaust you'll be fine. Actually, you don't have to start on #1 to do this, it's just my routine.
While you're doing all of this, check each pushrod and rocker. Another thing to look for is a pushrod stud being pulled out of the head, this usually becomes apparent when you look at all of the rockers, and there is a lot more stud sticking out of one, more than the rest. At that point you can drive it back in and pin it using a roll pin, or if you'd like, pony up the bucks for a set of screw in studs. If you check the pushrods, rotate them as you pull them out of the head, otherwise they can stick in the lifter and pull the lifter out of it's bore. Which really sucks. If there is no problem apparent with any of this, then it's either a bad lifter, or a bad cam, or possibly a bad valve or guide, but you should be able to see that.