[Solved] 3.8 low oil pressure

[paydase]

That's an issue already addressed at length, but I did not find a topic addressing in detail the disassembly of the oil filter housing and the inspection of the oil pressure release valve (OPRV), hence I thought it would be better to open a new thread describing the operation with detailed pictures.
Hope that will help other people in the future.

This thread follows on the low oil pressure I encountered on my 1961 OTS, mentioned here:
viewtopic.php?f=4&t=18638

The aim (and hope) is to find out that the low oil pressure, especially with hot engine, would be due to a not well closing OPRV rather than worn bearings in the crankshaft assembly.

To have easier access, I first removed the splashguard aluminum plate under the right hand side of the engine.
I decided to let the oil return hose attatched to the sump to avoid draining oil and just eased the top collar to be able to detach the hose from the oil filter housing later on.

I then removed the oil filter canister.
I was surprised to find a strange kind of seal made of cork, stuck on the base metal plate:

IMG_20220827_102529 (2).jpg (236.53 KiB) Viewed 3899 times

A slight crushing of the cork shows that the oil filter end was substantially pressing on it.
First question: is that cork necessary to ensure a proper sealing of the filter end on the plate?

I thereafter unbolted the four long bots attaching the filter housing to the block.
The filter housing came gently and I disassembled the returning hose to allow full removal.
The trace of the filter housing seal can be seen on the block. The holes correspond to the usual configuration:

IMG_20220827_110226 (2).jpg (228.19 KiB) Viewed 3899 times

To be continued

[paydase]

On the other side, the seal remained stuck to the filter housing.
A close view shows the assembly of the OPRV inside the casing:

IMG_20220827_110128 (2).jpg (223.05 KiB) Viewed 3890 times

One can observe that the spring seems to be "leaning" a bit on the top right, not fully straight, as if it were slightly bent.

Another view from above shows the top of the brass valve:

IMG_20220827_112605 (2).jpg (220.36 KiB) Viewed 3890 times

Looking closely, it seems that there are slight markings on the inside of the bore, between the fins of the valve. Maybe an artefact...

The view from below shows the seat upon which comes the base of the valve:

IMG_20220828_171625 (2).jpg (220.12 KiB) Viewed 3890 times

No visible damage at first sight.

[paydase]

For security, in case of a defective OPRV, I sourced a replacement valve and spring:

IMG_20220829_155306 (2).jpg (170.71 KiB) Viewed 3888 times

When compared to the OEM, one can notice diffrences in the quality of the pieces.
The finish of the new valve looks coarse compared to the OEM piece:

IMG_20220829_160659 (2).jpg (223.42 KiB) Viewed 3888 times

Similarly, the new spring has ends that are not finely tapered as the OEM one, leading to an oblique stand when raised on its base while the OEM one sits quite vertically:

IMG_20220829_161002 (2).jpg (179.05 KiB) Viewed 3888 times

[paydase]

The visible difference when the valve is put of top of the spring may have an impact on the proper seating and pushing of the assembly inside the closed filter housing:

IMG_20220829_162900 (2).jpg (190.62 KiB) Viewed 3887 times

Obviously, if the OEM pieces are not defective, it looks to me better to keep them...
I am going to throughly clean the pieces and reassembly as original.

So my questions before reassembly are:
- should I keep the cork on the filter housing?
- may the bending of the OEM spring have an impact on the right sealing? (I have attempted gently redressing it, seems to have improved)

[abowie]

I've read your original topic.

In your position I'd fit the new valve and spring and see what happens.

If this doesn't help you can put a shim between the spring and the bottom spider piece that will have the same effect as fitting a stronger spring.

[Allrand]

Keep us posted, I'd be interested to see the outcome.

[paydase]

I've read your original topic.

In your position I'd fit the new valve and spring and see what happens.

If this doesn't help you can put a shim between the spring and the bottom spider piece that will have the same effect as fitting a stronger spring.

Andrew,

From my careful inspection of the OEM valve, it does not show any defect on its seat or on its fins that may hamper a proper seating or a good sliding in the bore.
Moving it manually inside the bore did not show any resistance either.
The new valve does not seem to be better. On the contrary, its coarser machining does not inspire confidence.

Wrt springs, although there is a small length difference, their mechanical resistance upon compression looks similar (albeit only tested manually).
When inserting and bolting it inside the casing, the OEM spring still shows a good mechanical strength. I have not measured it but it looks to me consistent with the force to be resisted at 6 psi (or 0.4 kg/cm2) that should be about 0.5 kg (the square area of the bore is about 1.2 cm2).
Here again, I feel more confident to reuse the OEM spring because of its straighter standing and maybe more even pressure distribution with its tapered ends when the spring will be compressed.

I still hope that the low oil pressure is not due to worn crankshaft bearings.
Maybe there were tiny debris that were sticking on the valve seat and that were expelled during the disassembly of the OPRV, as the assembly came out suddenly when I unbolted the OPRV due to the spring strength.
I will take care of throroughly cleaning the oil filter housing before reassembly.

For the next step, if no improvement, I think that fitting a shim would not increase the spring strength by a factor of more than two that would be required to increase the pressure from 3 psi (as currently measured when engine cold) to the about 6 psi normally required to open the valve.

Again I recall that in my case, the low oil pressure measured is not due to a bad sender as I replaced it with a verified good one (my 3.8 FHC one that measured 6 psi when engine cold).
Now maybe silly, could the too low oil pressure read on the dashboard be due to a low voltage received: contact resistances or a bad wiring by the PO along the electrical circuit (I have not yet tested that)?
Any tips to check it?

[ralphr1780]

Now maybe silly, could the too low oil pressure read on the dashboard be due to a low voltage received: contact resistances or a bad wiring by the PO along the electrical circuit (I have not yet tested that)?
Any tips to check it?

Yes, a mechanical gauge.

[paydase]

Yes of course, thank you Ralph.
I remained cautions about that approach because of the risks of spill out if installed on the dashboard, in case of breakdownn...

But if the reading after reassembly remains low, I will buy and install one.
It would be stupid from my part not to check the pressure with a mechanical gauge before embarking in a rebuild of the crankshaft assembly!

[Series1 Stu]

I'm not sure about your units, Serge. Do you really mean 6psi? Or should it be 60?

Your pressure relief valve certainly shouldn't be operating at such low pressures. I reckon it should take around 5kgf to move the valve.

As for the reproduction parts, I've given up on commenting because you just get shouted down. That said, what you have been supplied with is abysmal. Yes, the machined valve shuttle is of a very low standard (was that a piece of swarf I saw in your photograph?) and there can be no excuse for not supplying a spring with ground ends, it's not as though they are unusual.

If it was mine, I would reassemble the PRV and check the operating force. The apparent wear in the bore of the valve looks ominous though and the valve may have stuck in the open position.

Reassemble it and check the valve operation using weights. If okay, fit it back on the engine and check the oil pressure using a wet gauge. If you get low pressure again, replace the head unit.

Regards

[paydase]

Thank you very much Stuart.

Yes of course, should be 60 psi and 5kgf, my mistake.
It was challenging indeed to put the OPRV back in the housing.
Unfortunately I have no weights or device to easily check the operating force but at least the two springs had very similar strengths.

Regarding the quality of the reproduction parts, I concur with you about the low quality.
You correctly saw a piece of swarf that I had to detach from the valve!

Regarding the bore aspect, I am not sure it is as bad as it looks in the picture, but yes there are marks.
Here are two other pictures, one with the top of the bore without the valve:

IMG_20220828_171556 (2).jpg (207.44 KiB) Viewed 3735 times

and another one with the OPRV reassembled (in a different position compared to when disassembled):

IMG_20220830_105037 (2).jpg (201.99 KiB) Viewed 3735 times

I have checked that the valve can easily rotate in the bore when seated without the spring (not when compressed by the spring though, there is too much force).
I hope that those marks do not keep the valve stuck in open position.
Actually there is a small dimensional tolerance between the fins of the valve and the bore, allowing in principle such movements until the valve is seated.

I will make a reassembly, test the oil pressure, and report.

[chrisfell]

I bought a replacement spring many years ago. It was fitted only briefly. I placed a thick washer under the old spring, which has kept the by pass valve closed up to 60psi ever since.

[paydase]

Thank you Chris.
So same advice than Andrew if the pressure provided by the spring stops short of that required to close the valve.
I take good note of it.

[abowie]

My notes from a couple of years ago. This was on a newly rebuilt engine.

Oil pressure relief valve spring.

Measured at 9.5lb/in

Spring is 2.00 long.

Compressed length in housing is 0.75"

So calculated to need 12lb to compress it. Used kitchen scales and rod. Almost EXACTLY 12lb needed to move valve.

Hole is about 0.450. Area is 0.160in2

So cracking pressure is 75psi which is within the ballpark of 20% over for 60psi.

QED.

Installed 2 60 thou spacers. Increased pressure by around 10 psi

[abowie]

I've reread this thread. If I have things correct:

You have low oil pressure confirmed by using a different known accurate sender.

You have not confirmed this using a manual gauge, possibly not excluding an electrical fault with the gauge.

You wonder if this is due to a faulty overpressure valve. You also wonder if this may be due to a worn out motor.

You have removed and inspected the spring and valve head and seat. They look OK and the spring force is within the range you'd expect.

You have bought a new spring and valve head and you are not 100% happy with the quality.

If you just replace your old valve spring and head you're back where you started from and you get no new information.

Since you have gone to the trouble of buying new parts, why not fit one or both components and see if they make any difference? If they do, it adds evidence that the overpressure valve is the problem. If not, engine wear looks the more likely cause.

You could easily do an off car comparison of the force required to open the valve, as I did. Assemble the valve components into the housing. Place a rod of the correct dimensions into the valve and push down onto the valve until you see it open. If you do this on a set of kitchen scales it will give you the opening force, which I measured at 12lb. You can easily compare the different springs and heads.

[DWW]

I have heard somewhere of another test to ascertain whether the valve is operating correctly by clamping the oil return hose and seeing if the gauge reading increases, if it does it may mean the problem lies within the valve.

[Heuer]

Yes, you heard it here. Clamp the hose and check the oil pressure.

[abowie]

Yes, you heard it here. Clamp the hose and check the oil pressure.

Don't clamp it completely as that makes oil go everywhere. Ask me how I know :-)

[DWW]

"Yes, you heard it here. Clamp the hose and check the oil pressure."

"Don't clamp it completely as that makes oil go everywhere. Ask me how I know :-)"

[paydase]

Thank you everybody for the useful comments and advices.

I had read about the clamping trick.
But I was wondering how adequate stopping of the oil flow could be ensured as the hose looks to me to be thick and it would be necessary to practically flatten it, with risks to tear the rubber.
Also, if the hose is not flattened enough (OK, not completely), there would still be substantial leaking through the remaining hose opening, possibly more than what would happen with debris in the OPRV seating.
So the clamping test would be effective only if the spring would be so weak that the leaking through the OPRV would be substantial...
Comments?

Concerning the strength test of the spring I was hesitating to unbolt again the OPRV to do such a test (I have already reassembled it with the OEM spring and valve), as I fear that successive torqueings of the copper washers may damage them.
On my oil filter casing, there are indeed two (?) copper washers to seal the big bolt securing the OPRV and they look to me already stretched and difficult to extract/replace them:

IMG_20220828_165522 (2).jpg (194.19 KiB) Viewed 3543 times

Such washers are not sold by the usuals and I am not sure that it is easy to find washer(s) with the correct specs.
Maybe an alternative would be to anneal them in situ with a gas torch?
Please advise.

Also I have not received comments on the "cork" present on the outside part of the oil filter housing.
Any advice?