How to Adjust Valves on a GM 350 Engineby John Stevens J.D.
General Motor's 350 engine uses eight intake valves and eight exhaust valves. All sixteen valves open and close at specific intervals. If the valves are not adjusted properly the engine can idle poorly, backfire, and power and fuel efficiency can be substantially reduced. Thankfully, properly adjusting the valves on the 350 is relatively easy, although the valve covers do have to first be removed.
Start the engine and allow it to reach normal operating temperature.
Remove both of the valve covers. A single valve cover is located on either side of the intake manifold. Each valve cover is attached to its cylinder head with a total of four bolts. Two of the bolts are located on the top of the cover, while the remaining two are on the bottom. Remove the four bolts with a wrench, then lift the valve cover off the cylinder head.
Identify each rocker arm's adjusting nut. The 350 engine uses a total of 16 rocker arms. In the center of each rocker arm is a single nut. It is this nut that is either tightened or loosened to adjust its corresponding valve. Also note that the tip of each rocker arm rests on top of a metal rod, called a pushrod.
Start the engine and allow it to idle. Loosen the single nut in the center of one rocker arm with a wrench until a clattering sound is heard, then tighten the nut just until the clattering stops. Turn the adjustment nut in a clockwise direction one full turn with the wrench to complete the adjustment for that valve. Repeat the processes for the remaining 15 valves, then turn the engine off.
Install the valve covers. Each of the two valve covers use a single gasket to prevent oil from leaking onto the engine. These gaskets are not reusable, and must therefore be replaced. Peel the old gasket off of the valve cover, then apply a single bead of gasket sealer onto one side of a replacement gasket. Place the coated side against the inner lip of the valve cover, then apply a single bead of gasket sealer onto the opposite side of the gasket. Place the valve cover onto the cylinder head, then install and tighten each of the cover's four retaining bolts. Repeat the process for the remaining valve cover.