GMC 12599650 Arm,Valve Rocker

You can Select Your Vehicle to check if 12599650 fits your vehicle.

To remove the valve covers, first detach them from the cylinder heads. Proceed by loosening and removing rocker arm stud nuts, starting from the front of one cylinder head. Keep these nuts in separate containers that are labeled so you can put them back correctly. On 1998 models and prior ones, in case only pushrods have to be removed, loosen each nut just enough to enable you rotate the rocker arms out of the way for pushrod removal. Instead of using pivot balls, roller-rocker arms on model year 2000 and later are retained by bolts. Put away rocker arms and pivot balls with nuts for reinstallation later on. Take out pushrods and keep them apart to avoid mix up during installation utilizing a perforated cardboard box which allows organized storage. Examine each rocker arm for wear, cracks or any other damage focusing on areas where rocker arm faces contact with pushrods and valve stems. Make sure that hole at the pushrod end of each rocker arm is open and inspect rocker arm pivot area for wear, cracks or galling. In particular, replace all worn roller rocker arms along with new pivot balls on 2000 and newer models. Check whether there are cracks or excessive wear on pushrods by rolling them on a flat surface to see if they are bent. To install, lubricate lower end of every single pushrod using clean engine oil or moly-base grease; seat in their original lifter positions; apply moly-base grease to valve stems as well as pushrod ends before placing the rocker arms over studs. Install pivot balls and nuts making sure that flat side of each nut faces pivot ball. Tighten down the rocker arm nuts properly. Reverse order reassemble remaining components; start engine then check for valve cover leaks as well as valvetrain noise (Haines). Note too that most models do not require a valve adjustment except specific instructions provided here for valve adjustment on 1994 VIN Z engines including setting the engine to TDC, aligning timing marks, and adjusting rocker arm nuts for specified valves at TDC for each cylinder.

Ensuring a specific cylinder is at TDC and the lifters for that cylinder are on the base circle of the camshaft is important to prevent valve and piston interference when removing rocker arms and pushrods.

After detaching the valve covers, proceed to loosen and remove the rocker arm stud nuts.

Rotate the crankshaft to TDC on the compression stroke for the number one piston and tighten the intake valve rocker arms for specific cylinders. Rotate the crankshaft 360 degrees and tighten the intake valve rocker arms for other cylinders.

During inspection, each rocker arm should be checked for wear, cracks, and damage, as well as the rocker arm pivot area.

After starting the engine, you should check for valve cover leaks and valvetrain noise.

To remove rocker arms and pivot balls, first loosen the rocker arm bolts and then remove the rocker arm nuts, rocker arms, and pivot balls. Carefully store them in marked containers for proper reinstallation.

During this process, you should inspect rocker arms for wear, cracks, and damage, particularly in areas where they contact pushrods and valve stems.

Apply engine assembly lube to the valve stems and pushrod ends to prevent damage.

To remove rocker arms and pivot balls, first loosen the rocker arm bolts and then remove the rocker arm nuts, rocker arms, and pivot balls. Carefully store them in marked containers for proper reinstallation.

Storing the rocker arm stud nuts separately in marked containers ensures proper reinstallation.

The pushrods should be inspected for cracks, excessive wear, and bending.