Oil pump pressure bypass spring question

[paddy]

I have the 50-52 panhead oil pump.
I have oil pressure loss after oil heats up. The pressure bypass spring that I found in the pump is 1 and 26/32.
Book calls for 1 31/32 length spring.
Would this short spring cause oil pressure loss after oil is hot? Light Sender is accurate comes on at 3-4 lbs.After oil is hot light comes on and stays on guage goes to 0 .I still have flow.
I gotta order the correct spring but thought I would ask before draining oil to check pump.

[Tom Wilcock]

How is oil pressure achieved in a hot roller bearing engine? I can see it in a sleeve bearing engine but not in a roller bearing. I believe that flow is all that really matters
Tom

[T. Cotten]

Pressure, Folks,...

Depends upon resistance, which inhibits flow.

As the motor warms, the oil thins, and clearances expand, resistance drops, allowing more flow.

The bypass relieves excess pressure, and most likely is closed long before the warning light comes on.

.....Cotten

[dukekleman]

With all statements above being contributors to low oil pressure, a person must not forget about the oil pump body, gear and cover clearances. These are very critical to oil pump pressure when hot. Especially when dealing with dissimilar metals that the pump is constructed from and bolted to...gasket thickness is critical and should not be overlooked

[paddy]

Cotten....So the short spring would not cause my pressure problem after the oil heats up?

[dukekleman]

Paddy, in my experience, the shortened pressure relief spring has a greater adverse effect on pressure at cold temperature viscosity.

[T. Cotten]

Cotten....So the short spring would not cause my pressure problem after the oil heats up?

Have we determined you really have a problem, Paddy?

As Duke points out, a shorter/weaker spring would dump into the cam chest at a lower pressure.

Without tension measurements of NOS springs, we are "armchair engineering".

....Cotten

[paddy]

Ok so the correct spring will be here today. I will install and go from there. Meanwhile I have purchased as close to factory oil pump gaskets as I could find.
.006 thickness
In preparation of going to the next step of removing and inspecting pump housing and gears.
Not sure what exactly I am looking for?
Gear clearance wear, ?
broken key?
Thank-you

[dukekleman]

Paddy,
I highly doubt you'll have any broken key ways or gears in your situation. You will simply be looking for things causing excessive clearances. Examples would be thicker gaskets, thinned gears, scored gears, scored gear housing areas, loose fitting idler pin, gear to housing clearance and gear to cover clearances including the gasket thickness.

[paddy]

Dukekleman, we're do I find that gear to housing clearance and gear to cover clearance? I could not find any of that information that you are suggesting to check.

[T. Cotten]

I didn't want to re-live this, Folks,..

But back in the pre-digital era, I had to save a worn body with a late-model seal on the drive shaft.

Pumpseal.jpg

(I'll never do another.)

....Cotten

[dukekleman]

Paddy,
It's nice to see 0.004"
A granite flat plate, various grits of wet/dry sandpaper working towards a smooth finish RA can yield nice results in the end. Timing consuming as many know when building these older engines.
A lot of the time spent correctly past poor service work done over all the years...

[paddy]

Duke so we are sanding the face of the pump housing?

[dukekleman]

Paddy,
I'll surface the cover, and both sides of all 4 gears until all surface's are perfect . Then I'll surface the pump body on both sides until I achieve the correct stack up clearances. Any scoring in the body will need to be addressed

[T. Cotten]

Let's talk about hand-surfacing, Folks!

Not all of us have a granite plate or tombstone handy, but large stick-on abrasive discs are available, and thick glass plate if you are resourceful:

POLSHML3.jpg
(Tempered glass cabinet door with attached trim as found.)

I found that a figure-8 swiping pattern removes material quickly, but tends to round the edges, leaving it high in the middle; The final flat surface is best achieved with criss-cross swipes to produce as bright a cross-hatch as possible, to grasp the gasket.

....Cotten