I just did the valve cover gasket replacement 3 days ago. It's not hard but it's time consuming especially if you do like I did and write down the steps you took to take things apart and also took pictures for reference later if you get confused putting it back together. I also labeled hoses and electrical connections to make reassembly much more straight forward. I used the write-ups on this forum as a reference and then went for it. Most of the oil coming down looked to be from the back of the valve covers so I suspected either my cam plugs or the rear half moons were leaking. Some people said they put RTV on the cam plugs themselves but I decided not to since the FSM didn't mention putting any on the plug itself. I used a pair of channel locks wrapped with some tape to remove the half moons and they came out fairly easily but one side of each head is harder to get a grip on the half moon due to spacing. The driver side valve cover was the harder side due to the wiring loom in the way, and like others reported, the plastic harness for the wires was brittle and cracked in a few places when I was wrenching on it to get the valve cover out and in. I just reinforced the plastic wiring loom with some metal tape like you use for heating duct work and it looks like it will be fine. I put RTV on all the areas of the head the FSM suggested and reinstalled them with the new valve cover bolt washers. I also did the spark plug tube grommets and used the FSM recommendation of deforming the grommet by pounding it from one side with a screw driver and hammer and then prying it out. I bent the little retaining tabs out of the way, installed the new ones with a 32mm socket as suggested in the FSM, bent the tabs back down and it was pretty easy. No cursing required.
I've never owned a torque wrench. I just use the appropriate amount of force based off the bolt or nut size and use common sense knowing the properties of leverage. If I'm tightening smaller bolts, I use a 3/8" drive and I choke up of the ratchet to reduce how much leverage I have with the tool. For bigger bolts, I use a 1/2" drive and may use all the leverage I can get from the ratchet. I think if I was building an engine or something more critical, I would probably invest in a good torque wrench, but so far, I've done pretty well just by feel and I haven't busted bolts off. Things have stripped on me before but I think that was more from the threads being bad than from me over-tightening something. For the valve covers, I choked up on my 3/8" drive and I slowly tightened the bolts using a crossing pattern until they were all cinched up fairly tight. I honestly don't understand how you could crack the valve cover unless there was some type of gap between the cover and the head by tightening down one side completely and then trying to tighten the other side causing a flexing off the metal. If you tighten the bolts down evenly, I would think you would break the bolt before cracking the valve cover, because the bolts are fairly small.
The job took me around 8 hours. Much longer than others reported, but like I said, I took my sweet time writing down all the steps I took and taking pictures also. Using my notes, I reversed the procedure and crossed off things on the list as I put them back together so I wouldn't miss anything. In addition, I drew a diagram of the spark plug wire configuration, noted the configuration of the bolts and nuts that came off the upper and lower plenums and also labeled the other bolts and nuts that came off so I wouldn't be guessing where they went later.
So, in a very drawn out way, I'm saying you can definitely do this is you are mildly mechanically inclined and have the patience to take the necessary steps like I did to make the process much more straight forward and eliminate any guesswork. These Toyota forums are awesome and have saved me a lot of money. The parts for this job ran me around $130 on-line. I bought the two valve cover gaskets, 2 cam plugs, 2 plenum gaskets, the 16 valve cover bolt washers, and the six spark plug tubes grommets. It took me a while to finally generate the motivation to tackle this job and I'm glad I finally rose to the challenge. Out of curiosity, I got a couple quotes for this job, one from a Toyota dealership and one from an reputable shop specializing in Toyota repairs. The dealer quoted me around $1000 and the other shop was $650. I'm guessing if I shopped around, I probably would find a shop willing to do it for much less too.
The money savings doing this job was great, but more importantly, the sense of accomplishment doing your own repairs and the confidence you gain to take on future repairs is definitely worth more.
