This is the rear housing bore for the main bearing. Before installing the bearings, make sure this oil gallery plug is reinstalled. You can see it in the upper hole on the right side of the housing bore.
It's time to install the cam bearings. Before sticking them in the block, take a carbide deburring knife and gently chamfer the edges on the i.d. to make sure none of the bearing babbit gets peeled back when installing the cam. Then thoroughly clean each bearing with a lint-free cloth soaked in lacquer thinner.
Properly installing the cam bearings requires a specialized tool because they must be installed square to the housing bore or they can become deformed. A tool, such as this one from Goodson, is a bit expensive, so if you plan on building engines only occasionally, you will probably come out ahead to have your engine machinist do it. If, however, you plan to build your engines regularly, a cam bearing installation and removal tool will prove invaluable.
It's a good idea to spend an extra buck or two to upgrade to brass freeze plugs over standard steel. This is because most racers run pure water in their cooling systems instead of an antifreeze mix, and brass won't corrode with contact to water, like steel. An easy way to install freeze plugs so they don't leak is to use a seal driver just a bit larger than the outside diameter of the plug. Drive the plug until the outside of the driver contacts the block all the way around, and then you will know the plug is square in the bore. Also, it's a good idea to use red Loctite on the edges of the plug. It not only will help hold the plug in place, but Loctite also expands when it dries to help seal any scratches or gouges.
With all of the block plugs out of the way, it's time to start prefitting the rotating assembly. The first step is to completely clean all the components. Don't forget the galleries that feed oil from the main journals to the rod journals. Make sure to clean them out with a brush. If you don't have access to a parts washer (and if you're using your shop washer, please drain the old coolant and replace with fresh, first), you can use lacquer thinner or brake cleaner.
During the prefitting process, you will have the rods apart several different times. To keep from getting the caps confused, paint the side of the rod with machinists' dye and scribe a number (from one to eight) on both sections of the rod. This way, when you have them all separated, you always know which cap mates to which rod. We use a sharp-pointed punch for a scribe because it makes a nice, legible line.
The idea of prefitting the rotating assembly is to make sure you have the proper clearances at the rod and main bearings. Too little and you run the risk of spinning a bearing. Too much and you waste oil-tighter clearances allow you to run thinner motor oil. As a general rule, you want 0.001 inch for each inch of journal diameter. For example, a standard Chevy main journal is 2.45 inches thick, so you want the clearance between the journal and the bearing surface to be 0.0024 inch (give or take a half of one-thousandth). You can see that this requires some pretty precise measurements. Begin by installing the bearings into the main housing bores (the grooved half always goes into the block) lubricating the threads and underneath the heads of the bolts with motor oil and torquing them down to 70 lb-ft for the inner bolts and 65 for the outer. Although we're using a truck block with four-bolt main caps, blocks with two-bolt mains are usually good for upwards of 400 hp safely.