It's better to use some diesel fuel (as directed by the factory service manual) rather than oil, as it isn't as thick, so you're less likely to end up with bubbles, which will cause them to be soft, and not adjust properly.
Do *not* drain the lifters before you put them in, just collapse them - The lifters work by filling with oil, which keeps them against the cams instead of having to adjust them manually like solid lifters. The oil drains out of the hole at a very limited rate, which allows the clearance to adjust, and act as a lash adjuster (technically, our engines don't have tappet lifters which are usually perched on the valve stem, they have rocker arms and lash adjusters). You do not need to fill them with oil to lubricate, they will fill on their own in the engine as soon as the oil system pressurizes.
The proper procedure is to submerge them in diesel, collapse them all the way, use a pin or paper clip to open the valve and fill them all the way, then collapse them again to bleed all the bubbles out, remaining submerged the whole time. Put them in directly after collapsing them. The remaining diesel fuel acts sort of like packing your oil pump with assembly lube, so that the incoming oil will fill in uniformly.
When you first start they will fill with oil and the diesel will go harmlessly into the pan.
Quoting TMG:
The lifter itself would need to be lubricated inside with oil so the noise at start up is minimal. To do this you will need to insert a pin inside the hole then submerge it into the oil to soak it up inside. Before putting the lifter in, you would need to insert the pin again to remove any oil inside of it, you only need a coating left in order to lubricate.
Also, there is a tool out there that you can use to pop the rocker of instead of using a screwdriver or pry bar. It is made specifically for this purpose.
Hope this helps.
Jojo
