GMC 12681275 Rocker Arms

Detach the valve covers from the cylinder heads, then loosen the rocker arm pivot bolts one at a time to remove the rocker arms and bolts, followed by the pivot support pedestal. Keep track of the rocker arm positions for reinstallation and store each set of rocker components in marked plastic bags. Remove the pushrods and store them separately to avoid mixing during installation, noting the arrow indicating the front of the engine. Check each rocker arm for wear, cracks, and damage, particularly where the pushrods and valve stems make contact. Inspect the pivot bearings for binding and roughness; if worn or damaged, the entire rocker arm will need replacement. Ensure the hole at the pushrod end of each rocker arm is clear, and inspect the pushrods for cracks and excessive wear, checking that the oil hole is not clogged. Roll each pushrod across a piece of plate glass to check for bending. Lubricate the lower end of each pushrod with clean engine oil or assembly lube and install them in their original locations, ensuring they seat completely in the lifter socket. Apply engine assembly lube to the ends of the valve stems and upper ends of the pushrods, then apply clean engine oil to the pivot shaft and bearing of each rocker arm before loosely installing them in their original locations without tightening the bolts. Rotate the crankshaft until the number one piston is at TDC, then tighten the intake valve rocker arms for cylinders 1, 3, 4, and 5, and the exhaust rocker arms for cylinders 1, 2, 7, and 8, ensuring each bolt is tightened to the specified torque. Rotate the crankshaft 360 degrees and tighten the intake valve rocker arms for cylinders 2, 6, 7, and 8, and the exhaust rocker arms for cylinders 3, 4, 5, and 6, again tightening each bolt to the specified torque. Finally, install the valve covers, start the engine, and listen for unusual valve train noises while checking for oil leaks at the valve cover gaskets.