As promised, here is the full procedure I followed for replacing the valve stem seals. I determined that they probably needed to be replaced just a few months after I bought the truck, because it would run well on new spark plugs for a week or so, then get worse and worse, basically not burning the gas that entered the cylinders because the electrodes on the plugs would get coated with oil. The only place I could think of where this oil might be coming from was the valve area, which meant that the valve stem seals weren’t doing their job of keeping oil from running down the stems and into the cylinder. The theory was that after shutting the truck off the oil would run down and coat the hot electrodes and thereby degrade combustion performance. All this was and still is conjecture depending on what happens now that I’ve replaced the seals, but according to several of the mechanics I talked to it was a good theory.

I disconnected the battery before doing anything else, partly for safety and partly because I knew the truck would be sitting for a while and I hoped it would hold a charge better disconnected. Next I removed the valve covers by loosening the four screws in each. That was the end of the easy part. Upon removing the valve covers I found my first solid proof that this engine has been over heated. Everything looks burnt.

The next step consisted of loosening the nuts that hold the rockers in place over the valves and push rods. I loosened all the nuts at the same time. Here is a valve assembly with the nut loosened:

I decided to do one valve at a time to make sure I didn’t mix up any springs, rockers or push rods. The next step in the process was to remove the rocker and push rod, setting them aside in a clean spot while I worked on the spring. After this I threaded my compressor adapter into the spark plug hole to provide air pressure to hold the valve up against its seat while the spring was removed:

 The compressor needs to maintain pressure as long as the keepers are off the valve. I had a little trouble with my compressor overheating and shutting off while I was working on this, because its cooling fan was loose on its shaft. The first day I worked on the valves I could only get one cylinder done at a time, then I had to wait 45 mins or so for the compressor to cool down before moving on. I fixed the fan with some epoxy and that allowed it to cool better the next time I worked on the truck.