Remember to do a thorough cleaning of the cylinder head before starting reassembly regardless of whether it did or didn't go through valve servicing at an auto repair place. In addition, if it had external valve servicing done, the valves and related components should be in place already since the reassembly will start now. Afterward, smear some light oil on the stems and then put valve spring seat(s) in their right positions on the cylinder head. One needs to realize that there is a difference between old 3.3L engines which have inner and outer valve spring seats and the 2.4L, 3.5L, and new 3.3L engines with just a single valve spring seat. For older 3.3L engines, it is advisable to install the outer valve spring seat first followed by the inner one.Once fitted as required manual installation of valve seals over the tips using stems as guides then gently hit each seal down into its marked position at certain depth is performed.The assembler must be cautious not to bend or twist seals during installation because improper sealing on stems can result.For intake valves in 3.3L engines only, an installation tool is needed while exhaust valves normally have to have their O-rings slid into place.Slide valves onto cylinder heads then use a compressor tool to load springs retainers and locks onto them.Notably, inner and outer valve springs are used for 3.3L engines while single valve springs are applied in 2.4L and 3.5L engines.It is always important that one inserts the outer valve spring into the inner one when positioning these springs together on a 3.3 L engine so that paint marks or end of outer coil more closely wound will be closer to cylinder head.Always return old cylinder head parts back where they were taken from originally saved locations.