Rebuilt Engine, Super Low Oil Pressure :(

CaseyW

did you pack the oil pump rotor cavity with a light grease, like vasolene?
that helps the pump to quickly pick up a prime

and,, you can get a nice set of nylon bottle brushes at HF, Sumitt, probably even at NAPA.
when I get a block, head or crank back from the machine shop it is bagged,, but before the build I always run a brush through the internal passages, just to make sure they are clean and open..
For a solvent I use liberal amounts of spray brake parts cleaner.
I follow that with a blast of compressed air. If the part will sit for a day or two, before building,a spray of a non tacky rust inhibitor like wd-40 before it goes back into the bag.