How should I approach a 350 Chevy valve lash adjustment? It started idling roughly after I tightened it. Now, I'm worried that I've done something wrong.
warm engine, remove valve covers, use oil deflectors, loosen rocker nut till it rattles, tighten until it stops rattle, tighten 1/2 turn more slowly. book says 1 full turn, that when new, but you do what you want
the true way is, as mentioned by, markme60, is to loosen each rocker nut while running. be warned that you will sling oil EVERYWHERE causing a lot of smoke. if you have a spare valve cover laying around cut the center out of it just wide enough to get a socket thru (about 1.5 inch wide). this will reduce the amount of oil thrown around.
Back when I did this ... I used to tighten them 3/4 turn after the rattle stopped. Regardless of how far you turn it, do not get in a hurry doing this process. You need to go slow while finding the "rattle" point and then stay slow as you finish the tightening.