Low Oil Pressure

Hello Tractor Mechanics extradinaires!
I have a question about oil pressure in an 8N motor I'm trying to finish up. I have a rebuilt engine that I am afraid to run because the oil pressure isn't coming up. If I take the pressure line to the pressure gauge off of the return line (to the oil filter), it will flow out gently.
But I'm wondering how does oil build up pressure if it comes from the pump and through all of its passages and then to the filter then govenor back into the oil pan? Isn't there supposed to be something to restrict the oil pressure to cause it to build up?[b:4b457df9ad][/b:4b457df9ad]

Yes the very tight tolerances that all of the cam and rod bearings produce if sized correctly create back pressure on th oil pump. The oil pump needs to push oil through those very small spaces. Think thousanths of an inch.

Wouldn't the oil need to be restricted in some way in order to force it out of the tight clearances? It seems that without something to hold it back, it'll just run through the passageways and dump out the end.

I'm pretty sure that the tolerances are correct. I had the crank turned 0.020" over. All remanufactored connecting rods and bearing. Plastigaged everything! 0.002" max clearance.

A buddy of mine said that the oil filter housing has a tube or plate that has some specific sized holes for the oil to pass through before going to the govenor and oil pan. You ever heard of this Greywolf?

The oil filter does have some restriction built
into it,otherwise the pressure at the gauge would
be 0 or close to it. You should get a gauge to
adapt directly to the elbow that supplies the
gauge so that you can be sure that the pressure is
correct. Did you rebuild the oil pump? My old '41
9n,which hasn't been rebuilt in many years still
gets 45 psi cold and 20-25 hot,so something's
wrong. Did you make sure that the passages are
clear in the crankshaft? The bearing shells have
holes to pass the oil to the other bearings,and if
not correct,would rob the bearings downstream of
the errant shell.Hope none of that is happening.
lha

(quoted from post at 22:07:45 10/23/14) A buddy of mine said that the oil filter housing has a tube or plate that has some specific sized holes for the oil to pass through before going to the govenor and oil pan. You ever heard of this Greywolf?

Click to expand...

No I actually never heard that. Back pressure is built up in the oil galleries by the oil pump trying to push oil through a .002 space.

Think of a syringe. When you press on the plunger you are creating back pressure when trying to push liquid from the main syringe tube through the needle. Same principle.

(quoted from post at 21:21:00 10/23/14)

(quoted from post at 22:07:45 10/23/14) A buddy of mine said that the oil filter housing has a tube or plate that has some specific sized holes for the oil to pass through before going to the govenor and oil pan. You ever heard of this Greywolf?

Click to expand...

No I actually never heard that. Back pressure is built up in the oil galleries by the oil pump trying to push oil through a .002 space.

Think of a syringe. When you press on the plunger you are creating back pressure when trying to push liquid from the main syringe tube through the needle. Same principle.

Click to expand...

Oil pressure in an engine does not behave like a hydraulic system and pressure is not uniform throughout the engine.The bearing closest to the pump will see a somewhat higher pressure than the bearing furthest from the pump.

The oil line is a tee at the end of the main oil gallery and without some sort of flow restriction would drop the main gallery (and hence gauge) pressure to near zero. It woud be analagous to a fourth main bearing with VERY wide clearances. To prevent that the oil line elbow has a flow restriction in it as does the filter housing.

TOH

(quoted from post at 22:20:37 10/23/14) The oil filter does have some restriction built
into it,otherwise the pressure at the gauge would
be 0 or close to it. lha

Click to expand...

The oil filter has nothing to do with the oil pressure. It is a by-pass oil filter system.

(quoted from post at 01:01:31 10/24/14)

(quoted from post at 22:20:37 10/23/14) The oil filter does have some restriction built
into it,otherwise the pressure at the gauge would
be 0 or close to it. lha

Click to expand...

The oil filter has nothing to do with the oil pressure. It is a by-pass oil filter system.

Click to expand...

Of course it does. And the fact that is a bypass system is why it has to be restricted.

That filtration bypass is a tee tap directly off the main bearing supply and if the bypass flow has less restriction than the flow going through the bearings it will cause a drop in the pressure and flow to the bearings.

In fact the filter ALWAYS causes a drop in the pressure and that is part of teh design. The Ford engineers sized the bypass restriction to match the overall flow coming from the pump and maintain ~40 PSI gauge pressure measured at the bypass junction. Remove the tee tap and screw a oil pressure gauge into the back of the block. That will increase the volume of flow going through the bearings and you will get a slightly higher pressure than you had with the filter in the system.

In a full flow system ALL of the oil goes through the filter BEFORE the bearings. The bearings are at the end of the line and the restriction through the bearing clearances determine the final oil pressure. Consequently the filter in a full flow system does not need nor does it have a restrictor.

TOH

(quoted from post at 18:20:37 10/23/14) The oil filter does have some restriction built
into it,otherwise the pressure at the gauge would
be 0 or close to it. You should get a gauge to
adapt directly to the elbow that supplies the
gauge so that you can be sure that the pressure is
correct. Did you rebuild the oil pump? My old '41
9n,which hasn't been rebuilt in many years still
gets 45 psi cold and 20-25 hot,so something's
wrong. Did you make sure that the passages are
clear in the crankshaft? The bearing shells have
holes to pass the oil to the other bearings,and if
not correct,would rob the bearings downstream of
the errant shell.Hope none of that is happening.
lha

Click to expand...

Good questions Iha.
I know that all the passages are clear, I had it hot tanked, clean, and turned to 0.020" over. But I did not rebuild the oil pump. I errantly thought it would be alright since I took it from a motor that I had. I have a new pump today and I'm pulling the oil pan down to replace it this weekend. Thanks for the tips Iha.

That is a great suggestion OldHokie. I will disconnect and plug the oil filter supply line and connect a gauge to see whats up. I have a new pump to install and I going to jump on it Saturday morning. I have a fear that even with a new pump and most likely higher oil pressure, I will still be looking for something to hold the oil back to build up pressure.

Do you know if a 9N, & 2N, oil filter housing is the same as one for and 8N?

Warning. You cannot just replace the oil pump. Since
it is integral with one of the main bearing caps,
you should have the engine line bored if you replace
the oil pump!!

I know the stardard advice is to linebore the block anytime the pump is replaced, but, lineboring being expensive, is there anyway to measure a given pump and block to determine whether it is really necessary?

There seem to be a fair amount of people who do not realized it is necessary, don't do it, and get away with it.

(quoted from post at 10:39:49 10/25/14) I know the stardard advice is to linebore the block anytime the pump is replaced, but, lineboring being expensive, is there anyway to measure a given pump and block to determine whether it is really necessary?

There seem to be a fair amount of people who do not realized it is necessary, don't do it, and get away with it.

Click to expand...

Yes - bolt it up and check the hole for out of round. If it is less than .001 out of round you should be good to go.

However the bearing caps are machined "in situ" and as a result the halves are not perfect semi-circles. New main bearing clearances are specified as .0015 to .0025. That means the original align bore can't be off center wrt the parting lines and bolt holes by any more than .0005 total. So your chances of finding a "match" between two independently bored caps are slim to none.

People have done it and reported success. My question is success for how long? I mounted an old OEM oil pump on a miss-matched block I have in the shop. That main bearing web is of round by .002. Can you bolt it up and get the crank to turn. Maybe. But your oil clearance is are already way off and how long it will run without problem is anybody's guess.

My only other hands on experience with miss-matched caps was one of my first TR4 engine builds. I put one main cap on backwards. It was on the proper block and proper main. When I torqued it down the out off round misalignment was enough to crack the web in the block and crush one side of the insert.

So I have my doubts it can be done with long term success.

It is a common problem and I have toyed with ways to avoid a full blown line bore that requires pretty expensive equipment. I have considered trying to fit a replacement pump/cap to a block by machining JUST the new cap in situ to fit it to the old center line. Something like this:

• [*:23f1baac73]Mount a boring bar in the bearings on the other two mains and use them as the reference for the old centerline. It will be dead on the original block line bore.[*:23f1baac73] Adjust the boring bit to .0005 clearance on the bore in the front main web.[*:23f1baac73]Grind the parting line on the new cap back by .003 or so.[*:23f1baac73]Bolt the new cap on and feed the boring bar into the front cap to bring it into round with the original block centerline.[/list:23f1baac73]You will be taking just a light skim cut off the cap and an inexpensive piece of 2.250 TGP round bar would make a very sturdyand accurate boring bar. All you need to do is figure a way to power and feed it while mounted in the block. Shouldn't be too hard for a clever gear head :roll: Maybe someday I will try it just to prove it can be done ;-)
  
  TOH

quote="TheOldHokie"](reply to post at 05:57:55 10/24/14) [/quote]

Dear TOH,
You are right about the restrictor. I found it in the oil filter canister. It is located on the side of the center tube. The tube appears to do three things.
One - It provides a way to tighten the lid on by having the internal diameter threaded.
Two - The tube is hollow and connected to the drain line to the govenor.
Three - The hole in the side of the tube is what seperates the oil pressure side from the drain side of the oil galley system.

I think that I didn't get a reading on my oil pressure gauge because the oil filter can was still empty from being cleaned out and painted. The oil was just pushing against air in the system - thus no pressure. I think I get what you mean. Until the oil pump is trying to push the oil through that small orifice, there isn't any pressure. But once all the air is out and the pump starts working to force the oil through, then I should get a reading.
Of course this is still a theory for me until I get the darn thing started. I think me and my helpful buddy damaged the electrical or something. He had the idea to use a 12 volt battery using it to turn the engine over faster, which did start it up at the time. It even started a few times off of the 6 volt battery, but now it just cranks.
Gas drips out of the carberator onto the floor. It might be flooding out. The spark seems weak to me so I ordered one of the kits to convert it over to electronic ignition with a 40,000 volt coil.
I'll be back when I get the ignition sorted out to let everyone here know if my theory was any good. :wink:

I didn't see this till I had changed the pump. I just dropped the pan and swapped them out. It seems to be okay so far. I mean the crank turns as it did before. I hope it will be okay.

(quoted from post at 17:17:34 10/23/14)
Hello Tractor Mechanics extradinaires!
I have a question about oil pressure in an 8N motor I'm trying to finish up. I have a rebuilt engine that I am afraid to run because the oil pressure isn't coming up. If I take the pressure line to the pressure gauge off of the return line (to the oil filter), it will flow out gently.
But I'm wondering how does oil build up pressure if it comes from the pump and through all of its passages and then to the filter then govenor back into the oil pan? Isn't there supposed to be something to restrict the oil pressure to cause it to build up?[b:3df8279d06][/b:3df8279d06]

Click to expand...

This problem has now been solved! The machine shop removed a plug from the oil galley tube that distributes oil to the main bearings, rods, and cam journal. I was able to slide the cam out 1/4" to get the plug back in. All is well, thanks to everyone who posted a response!

(quoted from post at 15:51:37 11/17/14)

(quoted from post at 17:17:34 10/23/14)
Hello Tractor Mechanics extradinaires!
I have a question about oil pressure in an 8N motor I'm trying to finish up. I have a rebuilt engine that I am afraid to run because the oil pressure isn't coming up. If I take the pressure line to the pressure gauge off of the return line (to the oil filter), it will flow out gently.
But I'm wondering how does oil build up pressure if it comes from the pump and through all of its passages and then to the filter then govenor back into the oil pan? Isn't there supposed to be something to restrict the oil pressure to cause it to build up?[b:daf929acf2][/b:daf929acf2]

Click to expand...

This problem has now been solved! The machine shop removed a plug from the oil galley tube that distributes oil to the main bearings, rods, and cam journal. I was able to slide the cam out 1/4" to get the plug back in. All is well, thanks to everyone who posted a response!

Click to expand...

You are probably the first person in the last 5 years reporting those symptoms that didn't get the missing galley plug suggestion. And also likely the only one that actually had the problem ;-)

Glad you got it squared away.

TOH