Where did my pushrods go?

[In Montana]

I recently got a "free" 1973 J-4000 that I finally got running fairly decently. After about 200 miles of reasonable service, it began running more poorly than usual. This occurred roughly in conjunction with a low "steady" reading on the oil pressure gauge (always at about 10-15 psi, regardless of temperature, rpm, etc.). I figured that the sending unit was malfunctioning and didn't worry too much, but after another 100 miles or so, I finally discovered that two of my pushrods were missing on the left side(I haven't looked on the right side yet), and one was bent. A fourth pushrod disappeared into the block as soon as I loosened the rocker arm nut. I also noticed that there is absolutely NO oil circulating in the upper valve train. I plan on pulling the intake manifold soon to see what I can see.

Here is my current working theory on what occurred: My oil pump pressure relief got stuck open, reducing the available oil pressure so that it couldn't reach the upper engine, and causing some sort of damage. I am not familiar enough with internal engine mechanics to know if this means damaged tappets, camshaft, valves, or if the engine is even salvageable. It is still capable of driving about 50-60 mph, but it has poor power, and based upon header temperature, I can tell that at least three cylinders are not hot (two on the left, and one on the right).

Any suggestions on what I should anticipate and look for?

[Crazy_Jeepman]

They bend or break and drop under the intake valley. No oil to the valve train is a good indication of bad cam bearings, poor oil pressure. I would keep an eye open for another motor or rebuild what you have

[reddog]

With the "missing" :D pushrods the lifters are likely losing some oil the should be restricted by the pushrods. If the pushrod is bent and still between the rocker arm and the lifter that valve is not opening as far as it should. Of course the cylinders with the "missing" pushrods are not firing at all. Overall these are bad things to be happing in a motor running a wag 50-60 MPH down the road.

Kerry

[Stolen76]

I had the same oil pressure problem, ate a full set of mains in a month. The problem was a combination of a worn front cover where the oil pump gears are and also a problem in the relief pin bore. I bought a new pump kit, but had to use the old relief pin to get pressure. If you do a search on "front cover" you will poop up some pretty useful info on that situation and what others have done