Regardless of whether the head was sent to an automotive repair shop for valve servicing, ensure it is clean before beginning reassembly. If the head was sent out for valve servicing, the valves and related components will already be in place, allowing you to start the reassembly procedure directly. On all engines, lubricate and install the valves, then install new seals on each valve guide, gently tapping each seal into place with a hammer and deep socket until seated properly. Avoid twisting or cocking the seals during installation to ensure they seat correctly on the valve stems. Starting at one end of the head, lubricate and install the first valve, applying clean engine oil to the valve stem. Place the spring seat or shim over the valve guide and set the valve spring and retainer in place, noting that on 4.0L SOHC V6 engines, the valve seal incorporates the spring seat/shim into one piece. Apply a small dab of grease to each valve stem lock to hold it in place, then compress the springs with a valve spring compressor and carefully install the locks in the upper groove, ensuring they seat properly as the compressor is released. Repeat this procedure for the remaining valves, ensuring all components are returned to their original locations. Check the installed valve spring height with a ruler or dial caliper, measuring from the top of each spring seat or shim to the bottom of the retainer, and if necessary, add a shim under the spring to correct any height that exceeds specifications, while avoiding any shimming that would result in an installed height less than specified. Finally, apply moly-base engine assembly lubricant to the rocker arm faces and fulcrums before installing the rocker arms and fulcrums on the cylinder head studs.