GMC 12562923 Engine Cylinder Head

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To begin with, take off the rocker arm covers and then the intake manifold, making sure that the cooling system is drained to stop coolant from seeping into internal engine areas when the manifold and heads are removed. After that, remove rocker arms and pushrods by detaching both exhaust manifolds. Use a new head gasket and create a template on a piece of cardboard by outlining the cylinders and bolt pattern while noting the front of the engine for reference then punch holes through at the bolt locations. In 1/4 turn increments, loosen head bolts until they can be removed by hand following a tightening sequence in reverse. To maintain original positions, store bolts in cardboard holder. Take off heads carefully from engine and avoid prying between head and block when resistance is met to prevent damage of mating surfaces but instead use wood block and hammer to free out heads if need arises. To protect gasket sealing surfaces, place heads on blocks of wood. The cylinder head and block mating surfaces should be cleaned right off using a gasket scraper to remove carbon and old gasket material followed by lacquer thinner or acetone washes. Mating surfaces should be dry as any oil may result into improper gasket sealing resulting into leakage problems. Some blemishes may call for filing while others could necessitate machining; thus inspect these surfaces for damages that might have occurred before installing new parts. Chase threads in the head bolt holes with the appropriate tap then clean threads thoroughly. Set new gaskets over dowel pins in block; apply thin coat of sealant on both sides if using steel gasket before placing it ensuring raised bead faces up. Composition gaskets shall be installed without any sealant being used at all. Now, position heads atop block without shift mortification occurring to gaskets placement itself. Just before mounting the head bolts make sure that they are coated with non-hardening sealant like Permatex no 2 and then screw into their original positions tightening them by hand. Gradually torque the bolts to the specified torque following the recommended tightening sequence. Finish the installation with the rest of the steps in reverse order.

Store the heads on blocks of wood to protect the gasket sealing surfaces.

After installing all valves in both heads, check the valve stem O-ring seals for leaks using a vacuum pump and a special adapter.

The valves can be removed by compressing the springs with a spring compressor, removing the keepers, and then carefully releasing the valve spring compressor.

Clean the rocker arm pivot stud threads, cylinder head, rocker arms, pushrods, valve springs, shields, keepers, and retainers with solvent and dry them thoroughly.

Measure the installed valve spring height using a ruler or dial caliper, ensuring it matches the specified height.

Once the valves and related components have been removed and stored, the head should be thoroughly cleaned and inspected.

Remove built-up scale from the coolant passages and use a wire brush to clean the various holes and threaded holes.