Ok here is the situation,
305 engine just installed.
Mechanical guage installed with the plastic line (I hate that damn thing gonna go copper soon)
Anyway Oil pressure is at 20lbs when I start the engine cold, once warming up it goes to 0. It is zero at idle, and only about 5-10lbs at highway speeds.
I purchased a new oil pump, but while the pan was off I decided to take a look at the main bearings. They look decent but nothing special, however they didnt look worn enough to cause Zero oil pressure. But I have gotten new main and rod bearings and decided to replace them while I am down there. By the way the motor is in an 84 GMC 1500 pickup. Should I have a problem changing the bearings with the motor still in the truck? Is this a bad idea? The oil pan came off with no problem so clearance isnt an issue.
So is there anything I am missing? Any other causes for the oil pressure to be low? New oil pump, main and rod bearings should solve it right? (I know the rod bearings dont affect oil pressure that much but I have a knock at high RPMs and hopefully new bearings will eliminate that.
Also on top of the valve cover their is a long curved tube coming out of it. IT doesnt have a breather cap or PCV valve (It is on the other valve cover) Could this have any relationship to the problem?
Thanks for your time.
If any more info is needed just ask.
Robbie

 

Rod bearings DEFINITELY affect oil pressure, at least as much as main bearings do. Odds are that you will find a trashed rod bearing and that it's the cause of your problem.

The breather has nothing whatsoever to do with oil pressure. The curved tube is supposed to go to the air filter. The way the PCV system works, is that the PCV valve has vaccum supplied to it, so the engine is constantly sucking air and vapors out of the crankcase; the tube on the opposite valve cover is supposed to supply clean air into the crankcase to replace what is drawn out through the PCV valve.

Put in a regular standard volume M55 oil pump, except replace the stock bypass spring with a Mr Gasket spring, part no. 26.

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"So many Mustangs, so little time..."
ICON Motorsports

 

UPDATE.
I just finished pulling the last of the main and rod caps. No trashed bearing? What now? Can I expect to replace the oil pump, Rod and main bearings and still have no oil pressure?
Thanks
Robbie

 

Mic the crank.

Look behind the cam gear; make sure the plugs are in. There's another plug under the main cap, in the same place the oil pump drive rod is, except on the driver's side of the motor; make sure it's in there right.

If all of that is good, about the only other things that can cause this is a bad cam bearing or a lifter that's out of its bore.

Did the engine in fact have no oil pressure? Signs of low oil pressure distress? Oil burnt black within a few hundred miles, ticking noise from lifters (inevitable with no oil pressure), etc.; or is it possible that your gauge is merely defective?

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"So many Mustangs, so little time..."
ICON Motorsports