New and rebuit cylinder heads may be purchased from the dealers and auto parts stores in case of GM engines. Due to the fact that specialized tools are unavailable for dismantling and inspecting the heads and it may be difficult to source for replacement parts or due to the fact that it is usually cheaper for the home mechanic to purchase replacement heads and install them. The other possibility is that one can transport the complete cylinder heads to a professional auto-shops or General Motors dealership for general overhaul. A decision could also be made depending on other information if the complete engine is being overhauled at the same time. If the nuts, balls and rocker arms have not been removed, first, remove the rocker arm nuts, balls and rocker arms. Press down each valve spring with the valve spring compressor and unbolt the valve locking keys and do it to each of the valves. Slide out the keys and then retract the spring and lead to the removal of the spring cap, spring shield if used, spring and the spring damper. Align the cylinder head with a straight edge, and gauge for conformity in terms of warpage using a feeler gauge; remove all the valves and associated machinery and store these parts in cylinder head removal designated tray/box/stand so that they can be realigned as they were. Take out the oil seals installed at the stem of each valve and replace with new ones during reassembly, and where the bottom of the valve spring has additional spring shims, such should also be removed. Last, depressurise, disconnect the air-line, unlock and open the valve and finally slide each of the valves and their respective components in the numbered box or rack to finish the process of removing the valve mechanism and to also make sure that the parts of the valves are secured such that they do not get mixed up.