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low oil pressure in 1939 farmall H

R

Rich ORourke

Member
My farmall H 1939, starts at 40 psi oil pressure, in 30 minutes it drops to 20 psi. at 45 minutes it drops to 18 psi, at one hour it drops to 16 psi and then stalls. I would be grateful for any suggestions. The temperature of the engine and radiator stabilizes at 150 degrees. And yes there was plenty of oil in the engine.
 
I don't completely understand. Did the engine lock up, or did it just stall? Will it start up again? 16PSI oil pressure is not great but it should be enough.
 
The stalling is not related to the oil pressure if the coolant is full, and at 150 as stated. The oil pump probably has a warped cover and can be fixed pretty easily by using a flat plate of glass to "flat sand" the cover to make it flat again. The end play should be between .0005 and .001". The pump does not need to be removed to do the repair, but the pan does need to be dropped. Be sure the long bolts in the end of the pan go back in the same holes, and are not over tightened. If this turns out to not be the problem, the engine bearings (cam, rod, main) might be worn enough to be the cause. Many an H or M has had less pressure for years WO issues. So it is your call.
The gasoline cap may have a plugged up vent in it causing fuel starvation at an hour into the running. Coils and condensers are also heat sensitive, and prone to cause that symptom. I would see if it has good 1/4" blue spark when it quits before any other diagnosis. JimN
 
The engine did not lock up, it will start again very easily, after about 5 minutes. but will stall right out again until it cools a while.
 
The stalling sounds related to fuel or ignition and has nothing to do with the oil pressure. Check for spark when it dies, if you have spark look over the fuel system.


I've seen many H and M run with oil pressure barely registering on the gauge for many years. Low oil pressure can be caused by a bad relief spring in the pump, worn pump, or worn cam, rod, and main bearings. The general rule of thumb is 10 psi per 1000 rpm, so an H at 1750 rpm should have around 17 to 18 psi to survive.

If the engine isn't knocking or having at least a loud ticking sound, your oil pressure should be fine. In such a low rpm engine, volume is more important than pressure.
 
Sounds like a coil going bad or gas cap vent plugged to me. That oil pressure is on the low side but would not cause the symptoms you described.
 
Yep. Try the cheap fix first by removing the fuel cap. If that cures it, you need a new cap, but be sure to get a vented cap. If removing the cap doesn't fix it, replace the ignition coil.

Has the tractor been converted to 12 volts by chance? If so, the resistor may be bad, and that is why the coil is failing.
 

I asked a similar question here a few weeks ago about my Cub engine. It starts out at 30PSI, then as it warms up, it drops down to about 16PSI.

I was told that the most likely cause of the issue was the main and rod bearings being worn.

Don't bother putting SAE30 oil in it. Waste of money. I put 20W50 in mine, which should be thicker warm than straight 30. It didn't make a snot bit of difference.
 
Yes it was converted to 12 volts by a couple of real hillbillies who claimed to be mechanics, HaHaHa! The coil gets really hot as you run it, i am wondering if they wired it up properly so that it charges the battery. right now there is no battery on it, I start it with a harbor freight car starter (yellow one, like a little typewriter carry case), then I disconect it from the pos and neg cables and the tractor keep on running. there is a key start on it, I turn the key to the right and push down on the foot button starter with my foot and it always starts up on the first try.
 
The 15-40 or 10 40 oils are going to be thicker at operating temp. The second number is the effective viscosity at temp. JimN
 
Two real issues are now at hand.
An alternator needs a reference voltage to operate without making extreme volts (like 18 or more)
It must have a battery.
The coil is overheating. with a battery in it, it needs either a 12v coil (with the neg terminal to the distributor), or a ballast resistor in the lead going to the coil from the key/switch.
The following info is the main event. JimN
Bob Ms marvelous diagrams
 
I use Harvest King All Season Engine Oil in my 1943 H and it seems to work well, I have 60 psi when the engine is cool and about 45 when the temp gauge needle is in the "RUN" position. The stalling would not be an oil pressure problem, there must be something else wrong.
 
thanks for the tips, what weight is that oil you use, I have some 20W40 from my
dads old truck that is not opened yet, I wonder if I could use it in the farmall H? I noticed that the 12 volt conversion coil does get hot when the tractor is running. I thought if I put a heat shield on it, but it might be getting hot from the electricity running through it.
 
thanks for the tips, what weight is that oil you use, I have some 20W40 from my
dads old truck that is not opened yet, I wonder if I could use it in the farmall H? I noticed that the 12 volt conversion coil does get hot when the tractor is running. I thought if I put a heat shield on it, but it might be getting hot from the electricity running through it.
 
thanks, I just took apart the bottom of the oil pump and will check it for flatness tomorrow. I took off the screen at the end of the pump intake and cleaned it with Tylex soap and scum cleaner, it is an excellent degreaser and it is cheap and biodegradable and water based. I used a quart sized ultrasonic cleaner from Harbor freight, it really got all the sludge out of it well. Is the relief spring under the pllug on the side of the pump, or is it the spring with the clinder on the end of it that falls out when you take the bottom of the pump off?
 
Rich, do you have a magneto or a distributor? If you have a distributor, do you have a resistor on the coil? I think my oil is 10W40 or 10-40 All season.
 
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