Oil Pump Question

Greg Jones

Greg Jones

Well-known member
I have a newly rebuilt stock engine block and re-used a fairly new oil pump. Got it all together and checked the oil pressure (it's a stock, non-pressurized system) and using a 0-15 psi gage, the oil pressure pegged the gage. Normally at cold start up you should see about 5 psi and as the engine warms up the pressure drops. Yeah, I didn't pay a whole lot of attention to the oil pump as I have always regarded them as bullet proof. Time for me to rethink that thinking.

So...I have discussed this with my engine builder, and he has suggested some things. I thought I would toss this out to the crowd and see if anyone has experienced such a thing and what did they do about it.

I am of the mindset there is a restriction someplace creating an orifice effect and raising the pressure. I have not dropped the pan yet since my shop is freezing cold at the moment (hey, I'm 64 give me a break!) but will this coming week.

The engine started knocking which I think may have actually been moving the oil pump drive gear upwards, enough to get things out of place enough to make a noise.

My engine builder, a reputable guy, mentioned being sure there was a gasket in the bottom plate of the oil pump. Anyway, just asking if anyone else has come across this problem.
 
Hi Greg,

to the best of my knowledge, no gasket is mounted below. Because the pump will only deliver properly when the gears are flat on the base plate
 

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Werner said:
Hi Greg,

to the best of my knowledge, no gasket is mounted below. Because the pump will only deliver properly when the gears are flat on the base plate
Click to expand...

This is of special interest to me at this time.
I am working a diamond B. I took the oil pump out as it was totally covered with gunk/sludge. I was curious about what I found, that is....NO GASKETS, anywhere on this pump ??
Well, I went to a parts book. Sure enough there are several oil pump associated gaskets shown !!
-one where pump meets blk;
- one one at bottom of pump... NOT SOLID as shown in your pic, but only sealing perimeter of plate.
-oil pump screen cover.
My messes up pump had none.
 
The gaskets have nothing to do with the pump putting out high pressure. It’s a positive displacement pump and if the gears turn, the oil goes up. If that flow is restricted, the pressure will go up until something let’s go. Look for a restriction down stream of the pump output. Take the plug out and crank the engine with the key off. Oil should come out slowly if the flow is not restricted. You should be able to hold your finger on it.
It should shoot out if all the flow is coming out the plug hole due to a restriction. Good luck and let us know what you find.
 
If your gauge shows that response, there is clearly too much pressure. The pump output is pretty much unrestricted (or should be) so the problem will be in one of only a couple of places. I'd check that the top of the pump body just below the oil pump/distributor drive skew gear to see that there is clear passage for the oil to get through and that the hole where the oil exits the pump is clear. Also look at where it enters the valve chamber to make sure that is clear.
It has nothing to do with gaskets unless something (like a part of a gasket) has become lodged in an oil way between the pump and valve chamber.
Maybe you drop the sump, remove the oil pump, check it for blockage and try blowing air through from inside the valve chamber in the reverse direction. If you dislodge something, make sure it is removed from the engine or disaster awaits.
Please let us know what you find.
 
Hardtimes, I only see two gaskets in the parts book. A-6619-R for the bottom
cover plate 1928-29 and A-6626 for the bolt on screen cover. Don't see one
for block to pump, do you have the number?
 
I only use the upper gasket that fits under the filter screen housing . I would only use a gasket under the lower plate if the gears were binding on the lower plate . The thickness of the lower gasket adds area in the gear area and can lower oil pressure . I want to reduce open area around the pump gears as much as possible to increase pressure out put .
 
Last edited:
Is this a "new" oil gauge? Maybe it is defective. Try another one.

A loose timing gear will sound like a knock in the lower end.
 
Bob C said:
Hardtimes, I only see two gaskets in the parts book. A-6619-R for the bottom
cover plate 1928-29 and A-6626 for the bolt on screen cover. Don't see one
for block to pump, do you have the number?
Click to expand...

Hey Bob,
Thanks for your good work to spot/correct my error !
I just rechecked , you are correct...I think lol.
Bob,
A Q.
My bottom plate was without gasket. Bottom plate has slight scoring from gear rub. I read somewhere years ago... that plate can be flipped...for a new surface. Makes sense. What say you ?
No bottom plate gasket seems would make increased outlet pressure... what say you ?
Original pump. Cleaned up good !
 
Does the oil pressure drop after the engine warms up?

With 20w-50 oil, our oil pressure gage starts out pegged, than drops to 3 to 5 psi after warm up. At idle, warmed up, gage reads 1 to 2 psi. This is in the summer. Car is sleeping now.

Enjoy.
 
WHN said:
Does the oil pressure drop after the engine warms up?

With 20w-50 oil, our oil pressure gage starts out pegged, than drops to 3 to 5 psi after warm up. At idle, warmed up, gage reads 1 to 2 psi. This is in the summer. Car is sleeping now.

Enjoy.
Click to expand...


I run twenty w fifty motor oil in my model A engines and they operate exactly the same as you describe .
 
Greg Jones said:
I have a newly rebuilt stock engine block and re-used a fairly new oil pump. Got it all together and checked the oil pressure (it's a stock, non-pressurized system) and using a 0-15 psi gage, the oil pressure pegged the gage. Normally at cold start up you should see about 5 psi and as the engine warms up the pressure drops. Yeah, I didn't pay a whole lot of attention to the oil pump as I have always regarded them as bullet proof. Time for me to rethink that thinking.

So...I have discussed this with my engine builder, and he has suggested some things. I thought I would toss this out to the crowd and see if anyone has experienced such a thing and what did they do about it.

I am of the mindset there is a restriction someplace creating an orifice effect and raising the pressure. I have not dropped the pan yet since my shop is freezing cold at the moment (hey, I'm 64 give me a break!) but will this coming week.

The engine started knocking which I think may have actually been moving the oil pump drive gear upwards, enough to get things out of place enough to make a noise.

My engine builder, a reputable guy, mentioned being sure there was a gasket in the bottom plate of the oil pump. Anyway, just asking if anyone else has come across this problem.
Click to expand...
I run a Mike's affordable side cover with a filter and, run10w30 mobile one
on start up cold it will run up to 20+ lbs until warmed up then its back down to where it should 4000 miles no issue's
also no gasket on bottom of pump
 
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