No Oil Pressure

Suspect loss of oil pressure from worn engine bearings. A worn oil pump could cause low pressure but the bearings are more common. Since there has already been a loss of power, there's a good chance the crank shaft has been damaged, however, only an inspection will tell for sure. The power loss could also just be due to the collapsed lifters and the valves not opening fully to let fuel and air in.

Plasti-Gauge can be used to measure the bearing clearance for the crank shaft and connecting rod bearings. If there is excessive clearance AND there is no apparent damage to the journals, new bearings can be installed. They are available in.001" and.002" undersize which will take up a little extra clearance if desired. Check the back side of the old bearings to see if they are undersize already or if they are marked "STD" for standard size bearings.

Yup. The pressurized oil dribbles out from the bearings and back into the oil pan. The tight crank shaft bearing clearances makes it hard for the oil to get out and drip back down, so most of it goes up through drilled passages to the connecting rod bearings, camshaft bearings, and the oil passages that the lifters sit in. Even though the oil is oozing out, as long as it is under pressure it is isolating moving parts from each other. When there is excessive clearance, the oil can run out too easily so while there won't be much pressure, there will still be a lot of oil flow. That can save the crank shaft bearings but it will greatly reduce the amount of oil that goes to the other parts of the engine.

The first casualty is usually one of the connecting rod bearings. To get pressurized oil it depends on the crank shaft bearings to not let the oil leak out easily. The bearing clearance is typically around.003" -.005", about the thickness of two sheets of paper. It doesn't take much wear to make it easy for the oil to run out when there is nothing to hold the pressure in. At higher engine speeds the oil pump moves a larger volume of oil which overcomes that excessive leakage enough to turn off the warning light. Most sending units turn the oil light on at around 6 - 10 psi which is dangerously low already. Somewhere around 35 - 45 psi is typical.

The pressure will drop more when the engine is warmed up because the oil thins out and can run out of the bearings easier.