Whether it has gone to an automotive repair shop for valve servicing or not, the head should also be clean prior to reassembly. If the head was removed and taken for valve refurbishing, then you expect the valves and its correlated parts to be already in position to enable you begin the reassembling process immediately. On all engines, carry out valve lash and re-install the valves and new seals are fitted on the valve guide, seal should be gently pushed until it settles into its post. For the Seal installation in the V6 models one requires a hammer as well as a seal installer to place the seal around the valve guide with the valve spring seat already in place. It is specifically recommended to prevent twisting or cocking the seals during installation so that the said sub will correctly seat on the valve stems. On V8 engines, the seal and spring seat are integrated, and much care should be taken to check that replacement parts are equal to those earlier removed. Reinstall the valve lifters on V8 engines then clean and reinstall all the push rods with clean engine oil applied to the valve stems or moly-base grease. Insert the valve spring and keep the retainer off it, smear a tiny drop of grease on each keeper for convenience during assembly. Fit the valve spring with a valve spring compressor then insert the keepers in the upper groove of the keeper as the compressor is being discharged. Perform the same process for all valves while making sure that all the valves and their parts are put back to their proper places. An accurate measurement of the installed valve spring height can best be done with a ruler or dial caliper; the measurement is taken from the top of the spring seat or the shim(s) to the bottom of the retainer. In case of excessive height additional shims of the springs may be inserted beneath them to level the height up to the stated specifications but never shim the springs to a height lower than the set specifications. Last of all, lubricate the rocker arm faces and also the rocker fulcrums with moly-base grease before fixing the rocker arms and fulcrums on the cylinder head studs.