Oil Pressure Variations

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Oil Pressure Variations

Postby Ironlegs » Tue Jun 10, 2014 8:07 am

I own a Super A and a FCub and have some questions for all about oil pressure readings. I use SAE-30W detergent engine oil in both machines. After a cold start, both tractors show 25 to 30 psi pressure on their guages. After warming, both tractors show 10 psi or so pressure...barely in the "okay" region of their guages. I expect the oil pressure to drop when the engine parts are warmed and expanded and the oil viscosity is lowered by heating (is oil viscosity lower at high temperature?).

I have used the Super A for over twenty years operating with such oil pressure performance. I have used the FCub for four or so years at this performance. Are the oil pumps operating okay? I can find no new replacement parts or rebuild kits for the oil pumps...either on-line or in parts stores. I have noticed a bunch of used pumps on-line but they look well-used and problematic. At 10 psi warm, is the oil pressure enough to adequately lube the bearings and cylinder sleeves?

With both tractors over fifty years old, I have replaced rings and/or cylinder sleeves (Super A) after careful measurements, inspection and study of the guides and manuals offered on this website. Both machines have adequate power and performance is fine. Please offer your thoughts about whether 10 psi is causing undue engine wear and whether oil pump repairs are needed.
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Re: Oil Pressure Variations

Postby Eugene » Tue Jun 10, 2014 8:51 am

Ironlegs wrote:Please offer your thoughts about whether 10 psi is causing undue engine wear and whether oil pump repairs are needed.
Low oil pressure is usually caused by wear in the engine bearings; rod, main bearings and sometimes cam shaft bearings. Oil pump is not normally the cause of low oil pressure.
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Re: Oil Pressure Variations

Postby Hengy » Tue Jun 10, 2014 9:03 am

Agree with Eugene. It is not "too much" of a problem unless the pressure falls into the red. As the tractor warms up, the oil thins. That is the primary reason that the pressure drops...It can push out past the rod and main bearings more easily when thin than when thick. Merlin has the older style gauge, and when cold, the pressure goes all the way up to the left at high-idle. When warm, it is about in the middle of the gauge at high idle. When at low-idle warm, it goes just above the "red" zone, but significantly enough that I don't worry about it much.

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Re: Oil Pressure Variations

Postby Matt Kirsch » Tue Jun 10, 2014 9:28 am

Two unfortunate truths about low oil pressure:

1. Thicker oil doesn't help. Thinking so borders on denial.
2. It's never the oil pump. Thinking so borders on denial.
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Re: Oil Pressure Variations

Postby Denny Clayton » Tue Jun 10, 2014 9:44 am

Your oil pressure is just fine.
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Re: Oil Pressure Variations

Postby SONNY » Tue Jun 10, 2014 11:06 am

I am running on less than that on some of mine!---I just dont pull them very hard and they do ok for me.--its when you start up and have NO pressure is when you better be shutting down fast! thanks; sonny
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Re: Oil Pressure Variations

Postby Jim Becker » Tue Jun 10, 2014 12:39 pm

10 pounds is kind of minimal but should be OK. When you do major work on an engine, you should check end clearance on the oil pump gears. The A/Super A etc. engine has a die cast bottom plate on the oil pump. That plate is prone to warping as well as wear. You can hand lap that plate with fine abrasive paper on a smooth surface. Depending on how bad it was, you could improve the oil flow quite a bit.
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Re: Oil Pressure Variations

Postby John *.?-!.* cub owner » Tue Jun 10, 2014 12:48 pm

You did not mention if the 10 pounds was at low rpm or higher rpm. If at low rpm, that is normal to great for old IH engines. if at higher rpm, then you might want to consider checking the crankshaft bearing clearance.
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Re: Oil Pressure Variations

Postby Ironlegs » Tue Jun 10, 2014 2:56 pm

Some follow-up to the questions posed...the 10 psi warm operating oil pressure on my tractors is at high speed under load. At high speed, no load the pressure may increase 3 psi. At idle and no load, warm engine the oil pressure is right on the minimum portion of the okay (white) gauge zone.

I bought some of the plastic string material used to measure (crank to connecting rod bearing clearance) about two years ago. I measured at least two of the four crank to connecting rod journals and at least one of the crank to block journals on each tractor and found them to be lightly worn. I remember probing these bearings with thin shim material and shaking the shaft and rods individually without detecting any clearance.

Although I agree that the oil pumps would be less at fault for low pressure, I'm sure they're well worn causing their peak pressure capacity to be much lower than it was intended to be. The Super A is a 1951 and I know I've put about 125 working hours per year on it for 24 years (3000 hours) and it was 39 years old when I bought it! Previous uses were farming...grapes, truck garden products.
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Re: Oil Pressure Variations

Postby Eugene » Tue Jun 10, 2014 7:23 pm

Jim Becker wrote:10 pounds is kind of minimal but should be OK. When you do major work on an engine, you should check end clearance on the oil pump gears. The A/Super A etc. engine has a die cast bottom plate on the oil pump. That plate is prone to warping as well as wear. You can hand lap that plate with fine abrasive paper on a smooth surface. Depending on how bad it was, you could improve the oil flow quite a bit.
The Farmall Cub's oil pump contains a wear plate. Looks like a brass figure 8. The wear plate is self adjusting, using oil pump pressure behind the plate to maintain clearances and oil pressure.
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Re: Oil Pressure Variations

Postby John *.?-!.* cub owner » Tue Jun 10, 2014 10:03 pm

Eugene wrote:
Jim Becker wrote:10 pounds is kind of minimal but should be OK. When you do major work on an engine, you should check end clearance on the oil pump gears. The A/Super A etc. engine has a die cast bottom plate on the oil pump. That plate is prone to warping as well as wear. You can hand lap that plate with fine abrasive paper on a smooth surface. Depending on how bad it was, you could improve the oil flow quite a bit.
The Farmall Cub's oil pump contains a wear plate. Looks like a brass figure 8. The wear plate is self adjusting, using oil pump pressure behind the plate to maintain clearances and oil pressure.
I believe you are thinking of the hydraulic pump.
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Re: Oil Pressure Variations

Postby Eugene » Wed Jun 11, 2014 3:17 am

John *.?-!.* cub owner wrote:I believe you are thinking of the hydraulic pump.
Yes I was. Thanks for pointing out my mistake.
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Re: Oil Pressure Variations

Postby Ironlegs » Wed Jun 11, 2014 6:52 am

About hand lapping my Super A's oil pump housing plate...I'm getting the idea that abrasives are used to reduce the bolt flange thickness, thereby closing internal gaps with the pump's gears...let me know if this is the right idea.

With the Super A at 63 years old, I'm always listening for bad sounds. I use this tractor for rough mowing and for snow plowing mostly. It's a rare day that I'm doing any field work with it now. I know it will get to a point where something will break internally or wear on internal parts will diminish its power to the point where I'll have a major overhaul to perform to keep it running.

I saw a post here fairly recently about engine knocking where low hydraulic fluid level was the cause...it's these tips and direction, only found here, that really help the remaining users of these machines. There are very few decent running Farmalls in my region, NW PA, and no informed users and mechanics...everything is Kubota, Ford-New Holland and sheet metal lawn tractors. Thanks for your responses.
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Re: Oil Pressure Variations

Postby Jim Becker » Wed Jun 11, 2014 8:21 am

Ironlegs wrote:About hand lapping my Super A's oil pump housing plate...I'm getting the idea that abrasives are used to reduce the bolt flange thickness, thereby closing internal gaps with the pump's gears...let me know if this is the right idea.

Yeah, that is the general idea. The bottom plate started out with a flat surface. Lapping it will take out any warpage and remove any depression worn into it by the ends of the gears. It may reduce the end clearance of the gears.


Ironlegs wrote:There are very few decent running Farmalls in my region, NW PA, and no informed users and mechanics...everything is Kubota, Ford-New Holland and sheet metal lawn tractors.

That area along Lake Erie was covered with fruit and vegetable farms. It seemed like every one of them had an A or Super A. There have to still be some experts around if you look in the right place!
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Re: Oil Pressure Variations

Postby John *.?-!.* cub owner » Wed Jun 11, 2014 3:01 pm

Before you start reducing the clearance, use some plastic-gauge between the ends of the gears and the housing. The specs are in the service manuals. You may find the pump is ok, and you need to look at rod and crank bearings, or at the governor idler gear bushing instead.
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