There's two different types of rocker arms. With most GMs they are carefully adjusted with the center nut. If you tighten them fully, the valves will be held open all the time and the engine won't run. The feeler gauge method is the painstakingly slow way of doing it if you have way more time than you know what to do with. The easiest way is to loosen all the nuts so the rocker arms are loose to start with. That means all the lifters will be be fully extended from light spring pressure, and the push rods will spin freely with your fingers. Now snug all the nuts down just until there's no free up and down movement in the rocker arm of push rod. Go another 1/4 turn. That's a safe starting point. Some of the lifters will be on the top of their cam lobs; some will not. To speed the process, turn the engine by hand about half a revolution on the crankshaft, then tighten only those that have a lot of play. Leave the rest alone. The engine should start and run that way but don't be surprised it you have a lot of lifter clicking. You'll want to fashion a piece of cardboard to direct the spraying oil back into the top of the cylinder head. While the engine is running and warming up, slowly snug each nut to stop the clicking. When they're all quiet, you can start the actual adjustment when the engine is warm.
Back off one nut about 1/4 turn. A misfire will likely develop, and go away in a few seconds as the lifter adjusts. Do that repeatedly until that rocker arm starts clicking. Now tighten the nut slowly just until the clicking stops. That's one extreme. From here on you need to count how many turns you turn that nut. Tighten it 1/4 turn. A misfire will develop until that lifter bleeds down. That could take as long as 20 seconds. When it smooths out, tighten it another 1/4 turn. You can expect to have to turn it a total of about two turns. You're looking for the first point at which the misfire doesn't clear up. That's the other extreme where the lifter is fully collapsed. Don't let it sit there too long because the valves are cooled, in part, through the contact with the seats, and right now you're holding it open and preventing it from closing and resting on the seat.
Back the nut off just enough for the misfire to go away. Now loosen the nut exactly one half of the number of turns between the two extremes. That will put the plunger of that lifter perfectly in the center of its range of travel. From there the lifter can pump up to accommodate a cold push rod, and it has room to bleed down when parts are hot and expanded. Do that to each rocker arm the same way.
Tuesday, December 31st, 2013 AT 1:50 PM