i have a 94 1500 chevy silverado with 128xxx miles on it been driven like it was made out of class for years. i recentely had it worked on because the fitting on the hose that comes off of the intake into the heater core broke so i couldn't keep coolant in my system. but when you break the hose loose the threads will break it is designed that way. I knew what i had to do but i didn't have the tools to take the threads out so i took it in. the shop that worked on it did not know that it will break. So they took off the intake manifold so they can remove the threads without having anything fall down. I got my truck back and the next day it have no oil pressure. it would start at 40 when the engine is cold and when it warms up it will drop down to about 5 to 10. I had to push the truck because i needed to get to school but it was still acting up. My dad say how bout we change the oil because i had 3000 miles plus on it and when im changing it there's so much grit in the oil. Its impossible to get that much dirt in a closed oil system. we change the oil and it doesn't help. we drove it long enough to have it warm up and no change. we look down and the harmonic balancer is wobbling, which makes us think my camshaft is going out. we dropped the oil pan and we find a piece of the thread that was broken off from the previous repairs. we took it back in the shop so they could fix it but all they would do was flush out the engine and do a pressure test. We dont think they did a pressure test because it wasn't in their notes. when we first took it in it was just a clicking every couple revolutions but now its a knocking that is constant they both are coming from the back of the engine. I believe that is it. If you have any ideas on what it is please don't be afraid to speak up. we are going to tear the engine down in the next two weeks.