I'm new to the forum. A week ago I bought an 82 300SD that is complete but in rather poor condition. It shows 242k on the odometer, but I don't think that's still working. I'm attempting to turn it into a reasonable driver.

My main concern is a noise that comes from the engine. It's a loud tapping, it sounds for all the world like tapping sheet metal stop sign with a tack hammer. It is in time with engine rotation--it gets faster when the engine turns faster. The engine also has remarkably little power, and the amount of power seems to vary rather wildly. Sometimes it barely has the power to reach 5 mph with the gas pedal hard to the floor, other times it seems kind of weak but capable of reaching 40 mph. The noise is loud enough that I haven't had the courage to take it up above 40 yet.

I have already changed the oil (but not the filter; had to order one), the air filter, and changed both of the fuel filters that are under the bonnet, and I have done a diesel purge. During the first few seconds of diesel purge, the engines shaking stopped and it started running much more smoothly. After a couple of minutes the tapping noise went away--and then came back. Since then I've not been able to get the tapping noise to go away again. Loosening the fuel lines at the injector to the point of creating a cylinder miss does not make the tapping noise go away. I can't really tell where the noise is coming from, except that it seems louder on the left (injection pump) side of the engine.

The oil pressure gauge tops out when the engine is cold, but shows rather low pressure when the engine is fully warmed up.

I'm guessing the next thing to do is pull the valve cover, inspect for timing chain stretch and set the valve lash--which I'm certain has not been done in years. And I guess, look for anything under the valve cover that might be making noise. Anybody know what a broken valve spring sounds like?