lowest oil pressure for engine to survive

[flathead4rd]

I run a 286 CI 8-BA with 20-50 oil. Runs about 50 psi at start up but when hot about 10 psi at idle. Have not had any problems in 10 years or more. I've been told that it isn't about oil pressure with a flathead it's about flow. Just my experience and I run it hard.

[Aarongriffey]

Old chevies of that area had 14 lbs. to the mains and to get oil up to the rockers.
The rods had dippers that were dipping into puddles that were full and running over with oil.
My dad had an old Oliver 70 farm tractor with a Continental 6 cylinder ohv engine.
The shop manual said, “remove the little oil galley plug and with the engine running the oil should barley trickle out. We worked hell out of that tractor and it never did quit and never showed any oil pressure. But those are different engines. Our V8s need at least 20 lbs. at speed
I’d drop the pan and check or replace the inserts. I’d also install an 80 lb. oil pump.
These engines are getting scarce.
Aaron Griffey
Hayward, CA

[Tinker]

anything above 0 to quote Bruce Lancaster. 50 hot is interesting. 5-10 hot is not out of normal and good.


Flatheads are not a high pressure oiling system. model A four bangers where just a oil delivery system.


If it's stockish... All that high pressure does nothing. Well it washes bearings. Relax it's all good.

[flatheadmurre]

Pressure and flow is what you need to get sorted out...as long as you have flow you usually get away with it.
With the exact same reading on a pressure gauge you can have very different scenarios...
You can have a good oilpump that is able to put out flow with a worn engine...it will run until the knocking and rattling scares the heck out of you no issues.
But the other way around a poor oilpump in fair engine will end up bad fast...
So just saying as long as you have a little pressure all is fine is a course diagnose.

[Tinker]

A gauge is a gauge it reads whatever. If you have a worn engine and a bad oil pump, well no flow or pressure.... If you have pressure you have some flow. Bearings help to create pressure... if the pump is bad as well... 0 is bad. But without pressure you have no flow.



Saying flatheads need more oil pressure then "we think they do". High pressure oil pumps are neat but not necessary. Hot oil pressure at a reading of 5-10 lbs is not a rebuild or bad motor scenario. It's just stock normal hot oil pressure.

[alanwoodieman]

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well we changed out the relief spring under the intake to NOS and also added a 1/4 washer this helped with the initial oil pressure but about the same running down the road, think we need to rebuild another engine--not sure a new op would help but at the cost of a gasket we might try. I do have a few used pumps ,including some 80 lb pumps, if I did this should we block off the reief spring under the intake or what?

[Mart]

What you just said makes sense. The 80 or 50 lb is a maximum. When warm, running down the road or at idle you are nowhere near the blow off pressure of the valve, so beefing it up makes no difference.

Personally I'd leave both valves in place so the oil feed to the timing chain area is regulated properly. But that's just me and I've never had to do it.

[flatheadmurre]

If it has the original pump putting in a 80 lb pump raises the flow so it will be able to maintain pressure better when hot.
The relief valve in the gallery should be left in place it serves dual purposes.

[G.M.]

Originally Posted by alanwoodieman

well we changed out the relief spring under the intake to NOS and also added a 1/4 washer this helped with the initial oil pressure but about the same running down the road, think we need to rebuild another engine--not sure a new op would help but at the cost of a gasket we might try. I do have a few used pumps ,including some 80 lb pumps, if I did this should we block off the reief spring under the intake or what?

I usually use a piece of 1/4" pipe 3/8" thick for a spacer. If it also
has a valve in the pump the valve with the weakest spring will
determine the pressure. G.M.

[alanwoodieman]

GM how did that 3/8" spacer affect the oil pressure?

[Kurt in NJ]

If you really want to know where your oil pressure goes use a pressure pot of oil to pressurize the oil gallerys before you put the pan on, then look where the leaks are, the bearings should drip, any missing plugs will make a big leak, and a steady stream out a bearing probably means too much clearance or a defect

I had to fix a Mercedes engine that the owner said had no oil pressure showing on the dash,that the gauge must be bad, it had 3 lbs at 2000 rpm on external gauge, it had been driven a month that way, I found 1/2 a bolt on top of the oil filter, upon removal of the pan 1/2 of the oil pump housing laying in the bottom,a windage tray bolt had been sucked in, no bearing damage, just a new oil pump

[Tinker]

So 80 to 50lb is normal, hot or cold...... hmmm

[V8COOPMAN]

Originally Posted by Tinker

So 80 to 50lb is normal, hot or cold...... hmmm

NO...…...80 or 50 lbs. MAXIMUM is normal, hot or cold. ALL words matter! DD

[Jack Shaft]

Is the hydrodynamic principle fulfilled?once that occurs oil pressure doesn't matter..model a engines relied on 3 inches of gravity to satisfy the bearing demand.



.001 bearing clearance per inch of journal diameter,,10 inch diameter battleship crankshaft? .010 bearing clearance..any oil pressure beyond whats needed cools and cleans the bearing,but isn't necessary for function

[Tinker]

Originally Posted by V8COOPMAN

NO...…...80 or 50 lbs. MAXIMUM is normal, hot or cold. ALL words matter! DD

It's a unicorn. Most flatheads are low pressure oil. It's not right to say a motor at 10lbs hot is a goner. I have a tight rebuilt that runs 50 at start and hot idle at 20. It's a good rebuild and no I didn't put a high pressure oil pump in it.

[tubman]

Originally Posted by Tinker

It's a unicorn. Most flatheads are low pressure oil. It's not right to say a motor at 10lbs hot is a goner. I have a tight rebuilt that runs 50 at start and hot idle at 20. It's a good rebuild and no I didn't put a high pressure oil pump in it.

Are you kidding me? Factory specs say 55 lbs at 2000 RPM and 25 psi at hot idle. My engines meet these specifications. I can't help it if you have a bunch of worn out boilers.

I thought one of the the purposes of this forum was to promote quality builds. I hope I'm not wrong.

[Tinker]

Tub you first to get at me. In a perfect world you will be the first to put another motor in it. Sure you can tell me how to convert to 12 volt too.

Flatheads will always be a low pressure system. 10-20 at hot idle is normal.

[Tinker]

Originally Posted by tubman

I thought one of the the purposes of this forum was to promote quality builds. I hope I'm not wrong.

You are right. Share your rebuild. I've shared a couple rebuilds here and on the yblock forum. Have at it.

[tubman]

Originally Posted by Tinker

You are right. Share your rebuild. I've shared a couple rebuilds here and on the yblock forum. Have at it.

It was done by a guy named "Dave" who runs the machine shop at the NAPA in Baxter. He told me that he had never done a flathead, but had worked for a Ford implement dealer and had done a bunch of 8N's and 9N's. That was all I needed to hear. Everything went great (and it didn't break the bank, either).

[Tinker]

Ya stop telling me how it is, show me.