Valve issue?

Hi!

The car is a 1989 Chevy Silverado C/K 2500 4x4
Wrote a thread earlier about knocking valves, opened the valve covers and the cylinderheads and valves where full of old,thick, sand like oil....guess the oil never been changed in a few years. So the knocking sound came from the pushrods, they didnt get any oil and i took out the rods that didnt get any oil and cleaned them and blew the hole where the pushrods go down with air pressure, and it became a whole lot better and quiet. But now there are 2 other problems, one is that when i adjusted the valves after i had the pushrods out i cant be able to get them right, adjusted them according to the chilton manual, turned the engine over to tdc and adjusted the valves, turned the pushrods until they where almost tight and then one full turn on the valve screw. Then turned the engine over one more time and adjusted the other valves, but then when i tried to start the engine it wouldnt fire, had to loosen up the valves, they are now so loose that the pushrod bearly moves....but the engine now feels slow and powerless, it almost stalls sometimes and i have to give it alot of gas to get it up to speed. Does anybody have any ideas why my valves cant be tightend? After adjusting the valves i tried turning the valve nut 360 degreas, 180, and even 90 but they where to tight and the engine wouldnt hold idle. Any ideas?

The other problem i my oil pressure, when cold the engine pressure i pretty okey,acording to the gauge in the car its at 30(psi?), but after driving for a while and the engines getting warm the oil pressure drops down to nothing if i dont give it gas, when in park and neutral, and standing still in drive. But when driving the car and it has gas the oilpressure is low but it never drops down to zero, could it be that i have to much dirt in my engine? could i try to flush it? how can i flush it? or could there be any problems with the oil pump? I´ve changed the oil 3 times now and the problem still stays...

Thanks for all the help i can get, hope you understand my writing, im from sweden and my english maybe isnt the best....

If the push rods were clogged as you say, it is possible that the lifters are also badly plugged and are not pumping up as they should. How many miles are on the engine? It may be time for a complete engine overhaul or a new short block, especially since, from the oil pressure issue, the internal oil passages in the engine may be badly restricted.

I would try some Seafoam or similar engine treatment (do they sell Seafoam in Sweden???) to help dissolve that oil sludge build-up. Be sure that it will treat the oil, fuel, and intake so that all sludge and varnish can be attacked. What probably happened is that one of the hydraulic lifters got some sludge stuck in it and prevented them from holding oil, causing a collapsed lifter. These are relatively easy to disassemble and clean. But if the passage to the lifter is plugged or severely restricted, then the block will probably have to be removed and cleaned.