low oil pressure in diesel

Anonymous-0

Well-known Member
I own a 1958-1962 01 series tractor. I don"t know what model, all of the numbers above the starter have corroded away. It is a diesel. When started the oil pressure is around 40psi but after warming up it drops to 18-20psi. I am wondering if I could get away with dropping the pan and installing new bearings? I cannot afford to have it rebuilt. I"m really hoping someone here can help me fix this as cheaply as possible. The tractor starts very easily and works pretty good otherwise.
 
1, replace the gauge

2, what oil are you using?

3, yeah.. GENERALLY you can pick up a few psi with a set of new mains and rods rolled in. you can just pull what you got and get the same size and know they fit and bypass the plastigauge.

not ideal.. but you knew that when you asked. so no big deal.

4, 18 psi hot idle, while pretty low for a red tiger.. is still enough pressure to keep stuff from bumping together. My most ragged out 172 gasser has similar pressures at hot idle after hours of mowing. ie. about 20-23 psi and cold throttle of 40-45.. 35 hot throttle

I plan on running her much longer before doing anything.
 
Ford used very hard beatings in those diesels that tend to ware the crank. I know that's not what you wanted to hear.
 
DO NOT install new bearings if the engine has a lot of hours on it. The cylinder ridges will most likely break the top rings or the piston ring lands.
 
These pressures are at speed, not idle. I need to keep this tractor running as cheaply as possible so any advice is welcome.
I don't understand how new bearings could damage the piston rings. Please explain.
 
If it was mine and I was on a very tight budget, I'd drop the pan and check the bearing clearances with plastigauge (support crank when checking mains). If the bearing clearances were out of spec, I'd roll in new bearings. If the clearances were within spec, I'd disassemble the pump and inspect for wear. If that looks OK, check the relief valve and spring closely.
 
don't know diesels,
but on gas engines with that problem,
I do the same as posted.
all new bearings same size that's in there, re-do the oil pump, 15w-40 or 20w-50 oil
and run it until time and money to do it right come along.
Does it fix everything?....no, but it will improve it a little.
And more importantly, a little peace of mind that the engine will keep all its parts inside, until I get to it the right way.
 
(quoted from post at 21:59:16 07/19/14) DO NOT install new bearings if the engine has a lot of hours on it. The cylinder ridges will most likely break the top rings or the piston ring lands.

How could that happen?
 
Sorry I did not get back to all you sooner. The way that you can really foul things up by installing new bearings in an old engine is this;
As the rod bearings wear, the piston drops a little in the bore, since the top bearing half is now thinner. At the same time, the cylinder ridge at the top of the bore gets a little wider, since the piston has dropped because of the bearing wear. Put in new bearings, and you now reset the piston travel upwards, like when it was new. Except that now, the top piston ring will hit the old, now wider ridge on the cylinder. Pow, broken ring or cracked ring land, or both. I suppose this same effect could be done on worn main bearings, since the whole assembly has dropped due to the worn bottom main bearing halves.
 
I understand what you are saying, in theory only. My question to you below was, are you speaking from experience here, or is this something someone told you in passing?

I'd argue that the opposite occurs, however. More than once I've seen rod bearings that have gone out, and the result is pistons hitting the cylinder head and/or valves. Why? On the exhaust stroke, the inertia of the piston coming up allows it to over-travel when the bearings are worn.

On the compression stroke, I could see your point, however on the exhaust stroke, I'd argue that the opposite occurs. This would negate the concerns you have about putting new bearings in an old engine.

I have never heard of your concern until you brought it up, and evidently, neither has anyone else who has responded.
 

If you roll in a new top bearing that is thicker and back to spec,, would it not drop the crank back down to center????

I would only worry about the ridge if you just replacing the bottom bearing.. On the last engine that I helped a bil do, we replaced all bearings except the thrust bearing as it was too tight... replace oil pump and he got another 90,000 out of the engine before he retired it. Oil pressure went back to normal. It was on a construction van used to haul equipment to and from the job.
 
In response to the other post, no, the piston is lifted when a new bearing top is installed. In answer to your post, "Yes absolutely", it has not happened to me or my friends who are aware of this danger, but there have been incidents especially in the old tractor fraternity I belong to where this has happened. Remember, the person who does this either 1.) did not know what happened after the calamity, and did not investigate, or 2.) won't tell anyone of the foul up. That is why many people have not heard of this little complication. I stand by what I have said. If someone wants to take a chance (especially on an expensive, high compression diesel) without addressing this ridge issue, at least they are aware if they read this forum.
 
OK, that's fine, however I stand by my theory as well, that is, your concern really is a non-issue for the reasons I stated earlier.

Many reputable engine manufacturers (Cummins, Detroit, Cat, etc.) have no problem with rolling in new main and rod bearings on a engine with high hours. If that's good enough for them, it's good enough for me.
 
(quoted from post at 13:09:58 07/21/14) In response to the other post, no, the piston is lifted when a new bearing top is installed. In answer to your post, "Yes absolutely", it has not happened to me or my friends who are aware of this danger, but there have been incidents especially in the old tractor fraternity I belong to where this has happened. Remember, the person who does this either 1.) did not know what happened after the calamity, and did not investigate, or 2.) won't tell anyone of the foul up. That is why many people have not heard of this little complication. I stand by what I have said. If someone wants to take a chance (especially on an expensive, high compression diesel) without addressing this ridge issue, at least they are aware if they read this forum.

So you are saying that you know that it has happened because other people have had unexplained engine failures who have either:

1.) Not known what caused the failure.
and/or
2.) Not admitted to doing what you claim was the cause of the failure.

And you are just proclaiming that this was the cause?
 
If I plastiguage the mains and they are out of spec how do I determine which size bearings to buy? I haven't worked on a tractor in 30 years and want to get it right the first time.
 
If I plastiguage the mains and they are out of spec how do I determine which size bearings to buy. I haven't worked on a tractor in 30 years and want to get it right the first time. Also, thank you all for taking the time to reply to my dilemma.
 
(quoted from post at 10:09:58 07/21/14) In response to the other post, no, the piston is lifted when a new bearing top is installed. In answer to your post, "Yes absolutely", it has not happened to me or my friends who are aware of this danger, but there have been incidents especially in the old tractor fraternity I belong to where this has happened. Remember, the person who does this either 1.) did not know what happened after the calamity, and did not investigate, or 2.) won't tell anyone of the foul up. That is why many people have not heard of this little complication. I stand by what I have said. If someone wants to take a chance (especially on an expensive, high compression diesel) without addressing this ridge issue, at least they are aware if they read this forum.

Tim, I can understand a concern along the line of thinking that the little extra thickness of a new bearing would push the piston a little higher, so that it could hit the ridge. However if that were to be possible it would be counteracted by the other half of the new bearing having a little more thickness and preventing the piston from getting quite as close to the ridge. Therefore myth busters have to declare this a busted suburban myth.
 
If the old bearings are standard size, they'll either be stamped with a "STD" on the backside, or nothing at all. If they are undersized, they'll be stamped ".010" or something similar.

If your plastigauge check shows that you are only a few thousandths out of spec, that simply means a worn bearing and you can go back to whatever size was already in there.

Be advised that standard size bearings are available in red and blue. I usually get whatever is cheaper.
 
Well, I have only one indirect involvement. A
friend of a friend bought a junk yard SBC. He put
in new rod bearings (I don't know how bad the old
ones were). He fired up the engine, and it
started burning oil, and continued to do so until
a complete rebuild several months later. My
friend said they found cracked top rings and
broken top ring lands, mix or match, on every
cylinder, which had ridges. Normal wear that this
SBC had did not do that kind of damage over the
course of time. Also, based on all of the
responses to this thread, if Schult wants to take
a chance and go ahead with the new bearings, if
there is enough slop in the piston pins, enough
slop in the bore, and the original bearings were
not worn thin, and the stars align, I will be the
first one to say that he may get away without
serious damage.
 
Please, I would like to see a direct quote from Cummins et al that the ridge on a bore can have no impact when new bearing halves are installed.
 
You won't find a quote from any of these engine manufacturers that states exactly what you say, however neither will you find from them any kind of a caution with regards to your concern. If it truly was a potential issue, I'm sure it would have been addressed.
 
Your explanation makes no sense. By restoring the
original height to the piston, you will run into
the ridge, of which there is no clearance between
the ridge and the top ring. The bottom half of the
rod bearing cannot overcome that simple fact,
unless it squashes the top bearing down, in which
case the engine won't turn. The bottom bearing
half is of no consequence, since the top of rod
rests on top half bearing. Work it out on paper
an you will understand. And, using an out of
place quote from a class B TV program does not
enhance your response.
 
If it was a legitimate concern, I maintain that the engine manufacturers would issue cautions about it. Since it's a non-issue, you won't find these types of warnings from them. I can't prove this to you because it's simply not there to be found.

As I have said before, I have worked on engines that had rod bearings go out where the piston smacked the head and/or valves because of the loose bearings. This is directly opposite of what you maintain, which is why I don't buy your theory.

I'm not trying to be rude or difficult. I just don't buy into your theory.
 

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