more oil pressure

Mark in MT said:
On a Model a engine, the oil pressure gauge reads the resistance of flow between the gauge port and the discharge pipe in the valve chamber. The higher the flow rate (RPM) and the higher the viscosity the higher the gauge will read. The pressure to the bearings will be the same, a gravity pressure of about 6" of head or about .2 psi. 100 psi on the gauge will not give you another ounce of pressure to the bearings, the gauge is just letting you know that the oil pump is still working. The model B is different critter all together.
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Nice post! It should make it clear to people how it works, if they don't already know.

The Model A engine doesn't rely on pressure to the bearings, it requires enough flow from the valve chamber down to the mains, so there is always enough supply to replenish what runs out of the bearings. If the oil is too thick, or the bearings are too worn, the supply can struggle to keep up with what's pulled from the wells.

The "Well" in the bearing is the "Pool" and the oil film on the bearing surface is the "waterfall". The crankshaft rotating pulls a film of oil from the well and drives it between itself and the bearing, creating a film of oil to cushion the crank/bearings.

This flow is created by the head of pressure Mark mentioned above, from the oil being pumped into the valve chamber.
 
For those that are more interested in the subject of oiling shafts, research hydrodynamic wedge. When the shaft rotates with oil present, the oil is dragged around the shaft, creating a "wedge" of oil, literally lifting the shaft off of the bearing. With the proper oil clearance, the shaft is suspended in a layer of oil, not touching the bearing.
 
Mark's description is spot on. I would also add that in a Model A engine the pan is simply a storage container. You are much better off with as much oil as possible in the valve chamber and dipper tray to circulate back into the pan to be pumped to the chamber and tray where it can feed to the mains and rods. Having an oil pressure gauge can be disconcerting when driving it goes to 0# and stays there for a few seconds and having a modern type attitude that tells you that you should ALWAYS show pressure. Fact is, when you only have short seconds of 0 pressure in a Model A it is doing exactly what it should and is a good thing. This happening indicates that the oil is in the valve chamber and dipper tray where it can do the most good. Not in the pan where it cannot lubricate anything.

If you want to see more oil pressure at the gauge, get one of the Afordable oil filter valve covers with the filter. The filter has a valve built in to keep the oil from bleeding back into the pan and provides a slight resistance to the oil so it will show a couple of pounds more than the stock system.
 
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