Oil Pressure Problem, it's non existant

[Lockleaf]

I have a 1985 720 4x4 with the Z24. I pulled the motor, cleaned the whole thing up completely, then tore it apart. I put in new pistons, rings, wrist pins, main and rod bearings plus all new gaskets. Everything went together just fine and it even fired up on our first try once it was back in the truck. After running it for a few seconds I noticed that my oil light was staying on and my oil pressure gauge was reading zero. At that point I shut it back off. I went back and read the service manual and realized that it said to fill the pump with oil before installing. I pulled the pump, filled it with oil, and spun it by hand to see if it was moving oil at all. The oil was pulled down in and started coming up the other side. I topped it off and got it put back in and got it and the distributor all lined up again. Then I pulled the oil filter to see if it had gotten any oil, and it was completely dry. It had not seen a drop of oil when I started the motor. So now I disconnected the ignition coils and just cranked the motor for about 10 or 15 seconds to try and get it to prime the oil system. Nothing showed on the oil pressure gauge and when I checked the filter again, it remained dry.

 

I also own an '84 720 with the same Z24. I jumped in it after disconnecting the coils to see if it would build pressure to show on the gauge just cranking over. It was not much, but it made enough pressure to show on the gauge inside, so I know the theory is sound.

 

I double checked my oil level in the pan, and added some more just in case. It's now about a 1/2 quart too full. Then I took off the filter and filled it with oil as well before putting it back on. Started cranking again. No change. Hooked the coils back up and started it again. Few seconds, no change. Still no oil pressure.

 

I put the oil pickup tube in with a new gasket, but all my friend and I can figure is that the problem is one of a couple of options.

 

1) The gasket on the pickup tube did not seal so it's like trying to drink through a broken straw.

2) There is a major blockage somewhere somehow in one of my oil passages

3) There is some trick to fully priming the oil system and without doing so, it will not prime

 

If you have any thoughts regarding this, please let me hear them no matter how inane they might be. If something is unclear please ask so that I can clarify it. And if there is some way to prime the oil system manual without spinning the crank, or even with spinning the crank, let me hear it. Any help on this incredibly frustrating turn of events would be helpful.

[DanielC]

I have removed the drive gear off the distributer drive shaft for a L-16, and usedthat, with an old worn out distributer, driven with a drill, counterclockwise to run the oil pump only.

['70 521 L16]

my l20b wasnt building pressure just by cranking at first after the rebuild either. as long as the pump and filter are primed it should build within 5-10 seconds of firing though.

[datzenmike]

The pressure relief valve on the pump may be stuck open. Oil will just recirculate round and round inside the pump. If you have another L, Z or KA pump, try it.

[kelowg]

u can also put washers on relief spring to increase spring pressure. for that matter,u can might b able to pop out relief and ck for junk in bore.

[datzenmike]

It happens. I had two oil filters split open. Lost most of the oil but saved the motor before finding the problem. The problem was a piece of casting sand or chip jamming the relief piston preventing it opening fully to relieve pressure. Around town at low speed was fine but out on the highway the pressure went through the roof.

[Spades]

This happened the first time I turned my Z24 over, turned out to be a bad oil pump(even though it was a new japanese pump right out of the box). I checked all of the ports, and oil was able to get though everywhere, and tried swapping filters. I ended up taking the valve cover off, spraying the valve train down with oil, spinning the engine over while I tried a few different tests to see if it would build pressure. I eliminated every cause but the pump, and replaced the pump.

 

No problems after that. I would assume it was dried up seals or a stuck open pressure relief valve like Mike suggested. Either way, you aren't the first one with a Z24 motor to experience this. My advise is to swap or fix the oil pump...do not run the engine without oil pressure!!!