Hummer 12629058 Head Assembly, Cyl (W/ Valve)

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To take away the cylinder heads, initially disconnect the battery cable and let out the cooling system while making sure that fuel system pressure is relieved. Unfasten intake manifold, coolant pipe, exhaust manifold(s), valve cover(s), rocker arms, pushrods as well as coolant air bleed pipe. For the left cylinder head, remove alternator with its bracket and detach ground strap from back of cylinder head. For right cylinder head take off dipstick tube and disconnect ground cables from front of cylinder head. Loosen the head bolts gradually in reverse order of tightening sequence until they can be removed by hand. Carefully remove the head(s) from the engine so as to prevent damage to mating surfaces. Put heads on blocks of wood for storing. When putting them back, ensure that both cylinder heads and block mating surfaces are clear of debris and clean up with a gasket scraper and brake cleaner checking for any possible machining damage as well. If necessary chase thread holes in block with a tap or brake cleaner followed by compressed air then replace all head bolts with new ones. Place new gaskets onto dowels in block before placing heads on top without interfering with position of gaskets then tighten head bolts to specified torque in recommended sequence using specified tools. Finally install coolant pipe using new gaskets; proceed to reverse removal steps thereafter; add coolant; change oil and filter; start engine & check for proper operation/leaks.

For the right cylinder head to be removed one should first drain the cooling system, remove the intake manifold, valve covers, pushrods, and exhaust manifold(s). Thereafter, one should proceed with removing alternator bracket and its mounting stud as well as spark plugs and spark plug wire support brackets. To loosen the cylinder head bolts in a specific pattern and lift the cylinder head(s) off the engine using a block of wood and a hammer. Store the cylinder heads on wood blocks to prevent damage. To remove left side cylinder head follows a similar process but also remove electrical junction block bracket, power steering pump bracket; disconnect ground wire, coolant temperature sensor and more spark plug wire support brackets. When installing the cylinder heads make sure that mating surfaces are clean and free from dirt. Look for any damages and use tap to chase threads inside bolt holes. Position new gaskets over dowel pins then carefully place cylinder heads onto block. Only tighten these nuts following recommended sequence, torque, angle of rotation specifications; thus coat threads of new cylinder head bolts with non-hardening sealant then tighten accordingly. Finally change engine oil and filter (leaks may occur upon starting engine).