Farmall 340 cylinder compression test

[Bill 1952]

Hello All,
I'm trying to determine what is causing the oil pressure loss on my Farmall 340 gas engine.
It shows about 41 psi cold.
As engine reaches operating temperature it drops to 10-15 psi.
A couple of questions:
1. One of the things I have checked is the cranking compression in all 4 cylinders. All 4 cylinder tested between 100 and 105 psi. Is that considered adequate? I can't find a spec on it.

2. What is the most likely cause of the oil pressure loss?

I appreciate any input.
Thanks.

 

[rustred]

that is the basic sign of a worn out engine. the camshaft and rod and main brgs are worn and the oil is running away faster due to the increase in brg. clearance. the cold oil has more vis to it but as it warms up the vis is lowered and runs past the brgs. faster. like pouring cold syrup on your pancakes compared to pouring warm syrup . compression is not bad i would say, plus how much oil are you going through?

 

[used red MN]

If that is at idle and the engine has no pronounced knocks, in my book that oil pressure is fine. Those compression readings are fine. Those engines are known to warp the gear cover plate on the oil pump. You can pull the pan and pump. Pull off the cover plate lay a sheet of 180 grit sand paper for metal on a flat steel plate and figure 8 sand it flat. When near flat switch the 320 grit. Reassemble it and go. Of course that is if you really can not find any else better to do. Your tractor is fine for enjoyment the way it is now.

 

[Bill 1952]

Thanks for the reply.
It will use a quart of oil about every 10 hours.
Getting a lot of suet buildup on the spark plugs.
I've been using 30w oil in it.
What do you think about trying 20w50 oil in it?

 

[Bill 1952]

Thanks for responding.
Today while testing it, we ran it at about 1/2 throttle.
Had a little over 40 psi cold. As it warmed up the pressure eventually dropped to about 10 psi at 1/2 throttle.
I've been using straight 30w oil in it.
What do you think about trying 20w50 oil in it?

 

[rustred]

20-50 oil will help a bit, and wont hurt a thing to use that. i presume u have a thermostat in it as that helps also to run them at operating
temp. myself i consider that at a quart a day overhaul time, but nothing wrong to keep using it as is. oil is cheaper. if she starts runs and
does the job good enough.

 

[Bill 1952]

(quoted from post at 01:32:48 05/27/21) 20-50 oil will help a bit, and wont hurt a thing to use that. i presume u have a thermostat in it as that helps also to run them at operating
temp. myself i consider that at a quart a day overhaul time, but nothing wrong to keep using it as is. oil is cheaper. if she starts runs and
does the job good enough.

Thank you kindly, rustred!

 

[BarnyardEngineering]

20W50 is a complete waste of time. I've never had it help the oil pressure.

I have had limited success with Lucas Oil Stabilizer. The oil pressure still dropped but not as much with a single quart in an engine that takes 5 gallons of oil. It's only a temporary bandaid, though.

Your engine is pretty well worn. If it's burning that much oil and the compression is only 100...

Flattening the oil pump cover is worth a try, but the behavior of the oil pressure indicates worn bearings.

 

[Bill 1952]

BarnYard Engineering,
Thanks for your input.
If the engine was in good condition,
what kind of compression pressure should I
be seeing?
I have not been able to find a spec on
that anywhere.
Thanks!

 

[Jim Becker]

For that engine 180#.

I tried (several times) to include the conditions for taking the readings, but the site filters keep throwing away my post.

 

[Jim Becker]

Compression pressures are based on the following conditions: Engine warmed up, battery fully charged, throttle wide open and all spark plugs removed. Compression gauge readings given will apply at sea level barometric pressure. For each 1000 feet above sea level deduct 3-1/2 percent. For engines with high altitude pistons, the readings given will apply at 5000 feet. Deposits in combustion chambers will increase readings to some extent.

 

[rustred]

20-50 is a waste of time wow I did say it would help a bit. You will not
see the difference though will the tractor gauges. You would have to use
low pressure master gauges to actually see 1 or 2 lbs of pressure
difference. Plus do the experiment with both oils at the same temperature
using a heat gun to actually see a difference. It will be small pressure
increase and would be a difference. Its just that that pump cant keep up
the normal pressure with worn bags. Same deal also as your garden hose
run it wide open no restriction and your pump will kick on almost as soon
as its turned on. Put a spray nozzle on the same hose and you can spray
for quite a while before pump kicks in cause your pressure is not dropping
as fast.