Author Topic: Not ADVISABLE to ADJUST THE PRESSURE RELIEF VALVE IN YOUR Q or U  (Read 3756 times)

chetbrz

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This is a continuation of my Post “Any Thoughts”

Cleaning and adjusting the pressure relief valve on the 1929-U was both good & bad.  It was good to clean it but very bad to adjust it and here is why.  (Use the crude diagram below for reference)

The line, which feeds the oil gauge, is between the pump output and the pressure relief valve.  Because of this the pressure relief valve only affects the pressure of the oil going to the motor parts. The gauge reading is only affected by the valve adjustment when the valve is opened to much thus causing a dangerous drop in oil pressure to the motor parts.  My assumption is that this is the reason the Plymouth Instruction Book states “…never to adjust this device…”.  The adjustment will have little affect on the gauge reading unless you completely deplete the amount of oil going to the engine bearings. 

The single eccentric in the oil pump is used to move both oil in the engine and air flow from the vacuum fuel pump.  Because of this, the total pressure out is equal to the sum of both inputs and the viscosity of the fluid.  Since the pump mixes air with the oil…, if the vacuum line is plugged up then no air is introduced to the pump and thus the pump will develop an additional 10 to 15 psi of oil pressure. (reason – air will compress at a much higher rate then oil)    Example:  Take the air out of your brake lines and they work much better.

This is exactly what the problem was with my car.   When I brought the car home it had no vacuum fuel pump and I still have not hooked it up yet.  The point being is that someone plugged the line.   Of course the last owner didn’t have the problem because he had a leaky oil pump cover gasket that introduced the needed airflow.  My problem presented itself after I replaced the leaky oil cover gasket. 

After cleaning and adjusting my pressure relief valve to minimum pressure my gauge was affected by maintaining 35 psi at idle and 50 psi at run.  Good.., absolutely not.  That meant that my engine was not getting the correct pressure at low rpm and probably at high also.   My engine starts to knock when I get into the 40 to 45 mph range and while driving it to the car show on Sunday it was starting to knock between 35 to 40.  I finally discover the above problem after the show.  I drove a total of 35 miles to and fro and most likely took some life out of my bearings.   

I intend to get everything adjusted back to spec before I run the car again.  Hopefully I didn’t do too much damage.  I am glad that the engine pressure stayed pretty close to the same otherwise I probably would have driven the car until I sized it up thinking that I fixed the problem.

The Plymouth manual is correct: 

NEVER ADJUST THE PRESSURE RELIEF VALVE IN YOUR OLD PLYMOUTH..

Chet...
« Last Edit: June 23, 2008, 04:12:03 PM by chetbrz »
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29UJohn

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Re: NEVER ADJUST THE PRESSURE RELIEF VALVE IN YOUR OLD PLYMOUTH
« Reply #1 on: June 22, 2008, 03:42:24 AM »
Chet,

I doubt you caused any damage to your car by cleaning and adjusting the oil pressure relief spring.  On a cold start at idle, it should read 35-40 lbs.  As it warms up, your idle oil pressure may drop to as low as 12-15 lbs, but should not be of concern. 

Your oil pump should not be mixing air with teh oil.  The previous owner did the  right thing by plugging the vacume port since it is not being used for the fuel pump vacume.  As for the vacume line - it does not draw much air if it is connected properly to a working vacume fuel pump.  It creates a vacume and should hold that vacume.  If air is introduced into the line in any great quantity, the pump will not draw sufficient oil from the sump. 

As for the releif valve, the problem is, you have no way of knowing if someone else had adjusted the relief valve before you obtained the car (as was the case for my engine).

The relief valve spring should be set to let off excess pressure - above 40 lbs.

However, at some point Plymouth changes where they read the pressure.  On my 29U the gage reading was taken down stream from the pressure relief valve. There is no port on mine at the pump.  When I obtained a pump off a 28Q with a port on the pump (as in yours), I was able to take pressure readings at two points - at the pump and downstream, by adding an extra pressure gage. 

I have noticed that the oil pressure at the pump may read 45lbs, while the gage reading from the downstream port measures about 38 or less.  As the engine warms up on an extended drive, the difference gets greater.  At 40 mph, the pressure at the pump still reads about 40 lbs, but my downstream reading is about 30 lbs (probably because my engine has a worn cam bearing).

These engines are pretty hardy.  A worn engine may run fine on 25-30 lbs of oil pressure hot, and 10 lbs at idle, with no detriment.  Idealy we all want our engines to be "like new", and a completely rebuilt engine should be.  But extreme excess oil pressure is not a good thing.

If I were you, I would plug that oil vacume port,a nd adjust the oil pressure releif spring to about 45 lbs when hot and running about 40 mph.  Obviouisly, this is a trial and erro thing, so make adjustments small - half a turn at a time and test drive hot.
« Last Edit: June 22, 2008, 03:46:35 AM by 29UJohn »
John
1929U 4 Dr

chetbrz

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The final resolution & corrections to previous statements.
« Reply #2 on: June 23, 2008, 03:52:52 PM »
Thanks John for the information, that was very helpful,

The point I was trying to make previously is that when faced with oil pressure problems adjusting the pressure relief valve is not the correct answer or wasn’t in my case.

The problem I was having was that my oil pressure was too high and by lowering the pressure without resolving the reason for the high oil pressure, especially in the 28Q & 29U which measure oil pressure before the valve, is a major mistake.   

As discovered over the weekend the oil path in my engine was gummed up and restricting the flow of oil to the bearing caps.  This was the reason for the high-pressure reading between the pump and the valve.  With the restricted oil flow going to the bearings all the pressure was applied against the only other path.., the pressure relief valve.   By lowering the pressure to minimum I still couldn’t get the operating pressure range correct.  (Never could get the pressure below 35-40 psi at slow idle) But by adjusting the pressure down I was in effect starving the bearings of what little oil they were getting.

Over the weekend I cleaned out the oil path as best I could with out removing the main bearing caps.  Through the use of high-pressure oil & air flow I was able to restore good flow through the engine.  I am still not 100% sure that all restriction has been removed.   After washing out the clog I was able to adjust my pressure relief valve quite a bit in from the minimum pressure setting I had prior.  (which is screwed out to the point that one more half turn and the Carter pin would no longer fit into the pin hole)

After some experimentation I was able to read 45 maximum psi (with a modern gauge) between the pump and the pressure relief valve both at medium and high rpm.  The pressure relief valve is now set at a more reasonable mechanical position and is neither at Max or Min but someplace in the middle.  The old gauge in the car reads 50 psi to the modern gauge’s reading of 45 psi. 

Current operating conditions using the old gauge, which reads 5 psi high on the high end of the scale:

Straight 30 weight oil

Cold engine slow idle:   35 psi
Cold engine high rpm:   50 psi  ( gauge no longer maxs out )

Hot engine slow idle:   25 psi
Hot engine high rpm   45 psi  ( gauge no longer maxs out )

The probable reality is 30 to 45 cold and 20 to 40 hot.  My engine bearings have quieted down so I think my problem is now finally fixed. 

Some corrections to previous statements.

I guess never say never but before you fool with pressure relief valve settings truly understand what is causing your oil pressure problem.  I believe the setting very rarely changes for no reason.

After further experimentation and observation the vacuum side of the fuel pump presents little affect on the oil pumps ability to provide adequate oil pressure.   My initial theory concerning plugging off the vacuum side of the pump was inaccurate. 

John,

When you have a chance could you provide a picture of where your oil gauge line is attached to your engine.  Hopefully there is a plug in mine that will allow me to measure pressure after the pressure relief valve.

Tks,  Chet...
« Last Edit: June 23, 2008, 04:21:17 PM by chetbrz »
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chetbrz

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What I have learned from all of this...
« Reply #3 on: June 24, 2008, 03:34:44 PM »
What I have learned from this adventure...

The pressure relief valve is nothing more then a plug held in place by a spring.  When oil pressure is applied to the plug it will push in depending on the tension of the spring.  When the plug is pushed in.., an outlet to the engine’s oil sump is exposed and excess oil pressure is drained off into the crankcase.

Theoretically the spring is designed for a defined tension and the adjustment is available for a minor compensation.  I believe when you get into the later 6 cylinder flatheads I was told that the valve wasn’t adjustable although three different spring weights were available.  The springs were color coded

My Observations:

  • The valve is least effective at low rpm which produces minimum oil pressure.  If you wish to increase your low idle oil pressure the relief valve will have little to no affect.
  • The relief valve is designed to drain off excess pressure and is most affective at high rpm when your pump is providing maximum oil pressure to the engine.

From discussing this subject with others who own 28 to 30U Plymouths.  I have founded out that in the earlier modal cars the oil pressure gauge is connected between the oil pump and the pressure relief valve.  On the later modals it is connected to the engine oil path after the pressure relief valve.  In my opinion the later connection between the valve and the engine path is the better of the two designs. 

My suggestions before you do anything.

  • Determine what your problem is before you compensate with an adjustment.  The adjustment may provide a better reading on your gauge but basically may not help your oil problem or provide better oil flow.
  • For high-pressure problems the most likely cause is clogged or restricted engine oil paths.  For low-pressure oil issues you may have leaky bearing caps which are allowing the oil pressure to bleed off or possibly a worn out oil pump.

A good rule of thumb that I have always used in my professional life as well as with my hobbies is “If it ain’t broke…, don’t fix it.  My oil pressure odyssey was started because of excessive and escalating bearing knock and not the gauge readings.   Sorry I don’t mean to lecture just pointing out that this is an area that should be very rarely played with.

What I have learned and been told by others during the course of my trouble shooting.

  • Pressure between the pump and the valve should be no more then 45 psi at high rpm.
  • Pressure in the engine path should not be higher then 40 psi and could be as low as 28-30 at high rpm.
  • Since the low pressure reading isn’t affected by the valve I have been told that pressure as low as 10 psi with a hot engine at low idle was acceptable and presented no problems.
  • Don’t trust your old gauge.  After 70+ years of service it stands to reason that it wouldn’t be dead accurate.  Hook up a new modern high quality auto gauge to evaluate your actual pressure readings.

Adjust for maximum pressure at high rpm.  Whether the oil is cold or warm the Maximum pressure should not exceed 45 psi before the valve and 40 psi after the valve.  Probably checking the adjustment with a warm engine might be best but shouldn’t matter, pressure is pressure at any temperature.  Turing the screw in will increase the pressure reading and turning the screw out will decrease the reading.  Feeling little resistance against the screw is normal and not a problem.

My thanks to everyone who provided information and discussion points to this topic both from this site, through email, and from the POC forum. 

Chet...
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29UJohn

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Re: Not ADVISABLE to ADJUST THE PRESSURE RELIEF VALVE IN YOUR Q or U
« Reply #4 on: July 03, 2008, 05:13:12 AM »
Chet,

It is hard to get a good picture of where the oil gage ine is connected to my engine - because the connection is hidden by the Starter. 

On my engine - the best way to descibe the location - there is an oil galley plug just above the oil relief valve.  If you draw an imaginary line from that plug straight back to the rear of the engine bock, the oil gage port is located there - at least it is on my engine.  It is so close to the starter that the oil line curves around the starter before going up and through the firewall.

PS - Note the brake fluid tank - it is different from any other I have seen, but it matches the description in the manual.  Even has a built in dipstick marked at 1/4, 1/2, 3/4, and full.

John
« Last Edit: July 03, 2008, 05:22:00 AM by 29UJohn »
John
1929U 4 Dr

chetbrz

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Re: Not ADVISABLE to ADJUST THE PRESSURE RELIEF VALVE IN YOUR Q or U
« Reply #5 on: July 03, 2008, 02:45:17 PM »
Chet,

 there is an oil galley plug just above the oil relief valve.  If you draw an imaginary line from that plug straight back to the rear of the engine bock, the oil gage port is located there - at least it is on my engine.    John

Thanks John,   

When I get a chance I will check this out and see if I have the plug.  It would be interesting to check the oil pressure after the valve. 

Interesting hydraulic oil reservoir.  This is the first time I have seen this.  The only other one’s I have seen are the tin can type and the early Chrysler one’s.

Happy 4th.    Chet…
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Satillite70

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Re: Not ADVISABLE to ADJUST THE PRESSURE RELIEF VALVE IN YOUR Q or U
« Reply #6 on: July 07, 2008, 04:43:23 AM »

    Something I just noticed in the photos on Chet's website, the oil pickup filter is totally different from mine.  Mine is a simple stainless steel open-top, perforated cylinder attached to the drain plug which seems to be magnatized.

    I also noted that my brake master cylinder is different, and matched the drawings in my owners manual.  They must have changed the design in '29.  The inlet port on top is not set in at an angle, it enters at a perfect 90 degrees as do the other two fittings, the outlet port and the pressure switch.

Chris

chetbrz

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Re: Not ADVISABLE to ADJUST THE PRESSURE RELIEF VALVE IN YOUR Q or U
« Reply #7 on: July 07, 2008, 08:53:44 PM »

    Something I just noticed in the photos on Chet's website, the oil pickup filter is totally different from mine.  Mine is a simple stainless steel open-top, perforated cylinder attached to the drain plug which seems to be magnatized.

    I also noted that my brake master cylinder is different, and matched the drawings in my owners manual.  They must have changed the design in '29.  The inlet port on top is not set in at an angle, it enters at a perfect 90 degrees as do the other two fittings, the outlet port and the pressure switch.

Chris

Yes.., the earlier 28’s had the Master cylinder you described. 

Also the motors were different from the 28-Q to the 29-U.

1928 - Maxwell Engine 170.3 Cubic In. 

1929 - 175.4 Cubic In.  Plymouth U,  This block is basically the same through the 196.1 ci engine offered in 1930-1932.  Mostly Bore & stroke differences only.  Some new holes added with the fitting of the water pump for the 30-U )

Chet...
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ski

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Re: Not ADVISABLE to ADJUST THE PRESSURE RELIEF VALVE IN YOUR Q or U
« Reply #8 on: August 08, 2014, 07:01:00 PM »
Old topic but here's a new picture.

SteveG

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Re: Not ADVISABLE to ADJUST THE PRESSURE RELIEF VALVE IN YOUR Q or U
« Reply #9 on: August 09, 2014, 05:24:06 AM »
Excellent Posts!

I have been messing around with the oil pressure issues for the last 11/2 years. No cents in kicking that dead horse...

Forward flash to the present day performance.

Engine reads 32 lbs. cold and a steady 28-30 lbs. warmed up and cruising 35 to 45 mph. (stock gauge is connected after the oil pump, on the line that goes to the center cam bearing.)

Hot idle around is 18 to 22 lbs.

Hot weather affects the oil pressures. Ambient temperature at 90 degrees or above drop the readings about 5 lbs.

I am using 20w 50 oil.

After reading all your posts, I think I may leave well enough alone.

What do you guys think?

SteveG

 


racertb

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Re: Not ADVISABLE to ADJUST THE PRESSURE RELIEF VALVE IN YOUR Q or U
« Reply #10 on: August 09, 2014, 05:10:04 PM »
20w-50 might be a little too heavy, just my opinion.

ski

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Re: Not ADVISABLE to ADJUST THE PRESSURE RELIEF VALVE IN YOUR Q or U
« Reply #11 on: August 09, 2014, 05:31:20 PM »
I was thinking the same thing.

SteveG

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Re: Not ADVISABLE to ADJUST THE PRESSURE RELIEF VALVE IN YOUR Q or U
« Reply #12 on: August 10, 2014, 03:56:17 AM »
20w-50 might be a little too heavy, just my opinion.

Thanx for your opinion.

I have tried a lot of different brands and weights. Seems I get higher oil pressure using heavier weight oil, especially in hot weather.

Perhaps heavier oil just flows slower causing higher pressure with a negative gain. I really do not know.

Can anyone tell what effect does oil weight have on oil pressure?

SteveG

« Last Edit: August 10, 2014, 03:59:15 AM by SteveG »

Des28Qau

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Re: Not ADVISABLE to ADJUST THE PRESSURE RELIEF VALVE IN YOUR Q or U
« Reply #13 on: August 10, 2014, 05:05:15 PM »
Hi Guys , Different opinions on oils has and will go on for ever .
As a Mechanic I do not recall getting much trade training on oil properties etc, .
C#? is Diesel & S#? is petrol grading the higher the second alpha ( ie SE or SH etc ) the better the oil for a modern engine, but dose not mean better for our old girls.
Remember oil flow is as important as oil preasure. ( Water flows better than grease )
Here is a re-post of a link I got from this site some time ago which is very ( probably over ) informative .
http://www.bobistheoilguy.com/motor-oil-101/
Regards Des
Des

racertb

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Re: Not ADVISABLE to ADJUST THE PRESSURE RELIEF VALVE IN YOUR Q or U
« Reply #14 on: August 10, 2014, 05:57:30 PM »
That link is a good read.  I think I posted that a while back :)

I know some guys like Rotella or Shell diesel oil 15w-40 because of the zinc content.  I was going to try it as well, but decided to stay with my QS 10w-30 I've been using for years after I read that article.  Still, everyone will have their own flavor that they like.

I was thinking of trying QS Defy 10w-30 because of its zinc content and because it's a synthetic blend, but not sure yet.