Engine producing a rattling sound and oil pressure is low

Hello people,

I have a 91 Chevy Cavalier RS, with a 4 cylindered engine.

I seriously need some advice. Two weeks ago, I had the head gaskets replaced. After that, I started to notice something strange in my car. The oil pressure needle tended to fall to 0 and the "Check Gauges" light used to turn on after a drove my car a little. When I first started up my car for the day, the oil pressure would be in the normal level, which is in the middle. After I drove it excessively, usually when I got off the highway, the oil pressure started dropping (that is when I stopped at any signal after getting off the highway). But when I pushed the accelerator the oil pump needle to go up. I checked my oil level and it seemed to be just fine. I consulted my mechanic and he told me that it could possibly be the oil pump. He told me that I should wait it out till summer, since the pump is ok and I shouldn't worry about the low pressure sign! Well now thanks to him, my car produces a rattling sound. It started when I was getting off the highway and on the ramp. On the highway my speed was mostly around 130 km/hr.

Now here is where I need some help. Is it possible that the rattling caused in my engine is because of faulty timing? Is it the crankshaft bearings? Now the mechanic says that I need a new engine (thanks to him!). Is he right? Or could it be that my car needs new crankshaft bearings?

god... ok. is your car idle set low? if it is, then at idle it will pump less (for that year). if your oil pump is not functioning like its supposed too, and you arent getting oil to all required areas of the engine, then you could have friction areas. things as cheap as pushrods and rockers or as expensive as crankshaft bearings. so many things could be the cause. step 1, step up to a synthetic oil (as long as you are sure you arent burning oil or leaking oil) that should help prolong the "engine failure". step 2, drive it very easy, dont break 3k rpm for any reason for about 25-50 miles. when was the last time you had an oil change? not saying that that is the cause of the fluxuating oil pump, just saying it might have to deal with the noises you are hearing. if its a small tick the rockers are dry, if its a scraping noise, u loose, hope the oil has enough time to fix it. your oil pump is probably shot, but dont give up on the engine because of a couple extra noises. engines are designed to run, not die.

btw, the price of crankshaft bearings, installation, balancing, and disassembly and reassembly is the cost of a new engine.