NOT ADVISABLE TO ADJUST THE PRESSURE RELIEF VALVE IN YOUR Q or U

[johnRFain29U]

Good info Chet!

My 29U engine has the pressure gage line coming off the engine block downstream from the relief valve and adjacent to the rear main bearing.  However, I obtained an earlier replacement oil pump (from Walt) and it has the oil pressure gage port coming off the pump oil outlet.  I added a second oil gage line and attached a modern oil gage to it, so that now I can see the presure at both points.

The oil pressure at the pump is almost always between 40-45 lbs at operating speeds, while the oil pressure at the downstream gage starts out at 40 lbs cold, but after the engine is warmed up good, it drops to as low as 28 lbs at 30-40 mph.  On a hot day after a long drive, at low idle the oil pressure drops to about 10-12 lbs.

 

[elmo]

Chet  is right on the later six cyl flatheads (i'm not sure from what year but it is at least 1935) the relief valve was not adjustable, and as he said they were color coded. the standard spring was unpainted, lighter than standard was painted red , heavier than standard was painted green . I have heard of some owners whose car has low oil pressure fitting a thin washer under the spring, it increases the oil pressure at the guage quite dramatically, but it is the same as screwing in the adjustment it is only disguising the original problem. this is taken from a 1935 Motors Repair Manual .
If high or low oil pressure is indicated on  the guage, and the proper amount and viscosity  of oil is in the crank case , the cause may be due to:  1, broken oil lines
      2, leaky connection in oil lines
      3, defective oil guage
      4, clogged oil pump or strainer screen
      5, worn oil pump gears
      6, loose main, rod or camshaft bearings.
      7, thicker than standard oil pump cover gasket
      8, oil pressure relief valve plunger sticking .
      9, distorted main bearing caps.
an accumulation  of oxide sometimes plugs the small hole in the oil guage connection this may be opened with a thin wire , the guage line should be free of oil when reinstalled .. 
I know this advise is for 1935 up but the principle should be the same for the earlier models

[30U sedan]

Thanks Chet, for all the information, this makes me feel alot better.

Dale

[chetbrz]

Sorry it took so long to reply........been very busy lately.

I have enjoyed catching up on all the fine information that has been entered since then.
But, I didn't see anything about how to adjust the relief valve.
Does anyone know the correct way to do that?
Do you think I would be safe if I just centered the adjustment screw with the cotter pin.
I also noticed that when I adjusted the screw in....there doesn't seem to be any resistance against the back of the screw.
Is this normal?
Does anyone have a drawing of the relief valve parts and how they work?
Sorry about all of the questions.....Just trying to get it right.

Dale

Dale,? What I have learned...

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.? Turning 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.

Good luck,? Chet...

[johnRFain29U]

Chet,

20 psi at idle on a hot engine is plenty.? 20-40 psi on a hot engine sounds great.

Glad your engine's knock cleared up.?

[30U sedan]

Sorry it took so long to reply........been very busy lately.

I have enjoyed catching up on all the fine information that has been entered since then.

But, I didn't see anything about how to adjust the relief valve.

Does anyone know the correct way to do that?

Do you think I would be safe if I just centered the adjustment screw with the cotter pin.

I also noticed that when I adjusted the screw in....there doesn't seem to be any resistance against the back of the screw.

Is this normal?

Does anyone have a drawing of the relief valve parts and how they work?

Sorry about all of the questions.....Just trying to get it right.

Dale

[chetbrz]

My six runs,on the original car guage, 45 psi at 45 mph 'cold' start (21C/70F)/30 psi at 50 mph when warmed up after maybe 10 miles ambient summer temps/15 psi on idle. I also use 30 SAE oil.
? I was going to post a reply the other day to warn you that you were bandading the high oil? pressure problem and the most likely problem was gum and you were starving your journals and who knows what else. The high pressure was 'back pressure' caused by the oil 'hitting a wall'. The 'wall' being gummed up orfices. As you say you still can not be sure all the oiling passages are open and with a babitted engine you're looking at a world of grief. Us sixes can just replace the inserts if there's not a great deal of scoring but you'd be into possible rebabbitting.
? ?I would pull the caps and using a fine water jet from one of those pressure washers hooked up to the house hot water,I would try to blast out all the passages in the engine before driving much more. The camshaft shaft bearings are a beggar to replace because of all the teardown required. Shops use hot water to do the same thing so you won't hurt anything.? ?

What do you think of this procedure for cleaning out the engine oil ports and bearings ?? ?I might do this when the engine is ready for some additional oil.

 Run the engine to bring up the temperature close to normal run temperature then shut it down.
 Add a quart of kerosene to the oil once the dipstick says it?s about ready for an additional qt.
 Crank in the pressure relief adjustment to force all pressure to the engine components.
 Fire up the motor and run it at high rpm for a minute or two.
 Shut it down, drain the oil, and replace with fresh.
 Readjust the pressure relief valve back to nominal position.

Chet...

[chetbrz]

I think my mistakes are worth posting here for those that have been following my odyssey.

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.?

Sorry for all my rambling but it does help me focus my thoughts.

Thanks to all who made comments, Chet?

[chetbrz]

I'm worried that my oil pressure relief valve may not be working at all.......
How do I check it?

Thanks,

THIS IS THE GREATEST BOARD........

I am sure your valve is working.., if not you might be experiencing problems like Yours truly.? The pump is capable of developing quite a lot of pressure and the values you are reporting seem OK to me.

Turning the screw in will raise the pressure and backing it out will lower the pressure.? I would adjust it back to where it was, that is if you remember which way you turned it and the number of turns.? But it sounds like you are OK.? Maybe try a straight 30 or 40 weight oil for the summer.?

Chet...

PS...? I changed the title of the post?, I guess never say never because there is always an exception.

[chetbrz]

Could you give more info on the pressure relief valve? My engine has had low oil pressure (20-30 lbs) since I replaced the bad copper tubing and replaced a leaking gasket on the oil pump.
I tried to adjust the relief valve but it seems to have no effect.
How does the valve work?
What do I need to do to reset it correctly?
Any ideas how to get the oil pressure back up?

I have just the opposite problem. With the relief valve set to minimum I can?t seem to get the pressure down below 50 psi at run without starving the bearings for oil.? I think I must have a clog in the engine system.? Before I parked the car in the garage I cranked the pressure relief valve in for Maximum pressure.? My thought was that maybe if there is some obstruction that maybe I could wash it out.? I drove the car about a half of mile at low and high speed.? The engine never sounded so quite.? What I intend to do now is attach an accurate oil gauge and adjust the pressure back down to a reasonable level. (30 at idle and 40 at run) Then I will be dropping the oil pan and checking the connecting rod bearings.? If they are in anyway loose I might be able to remove a shim or two to tighten up the system.? I have been thinking about piping in some high pressure air (30 ? 40 psi ) to evaluate the oil ports to the bearings.

My Take on things that may cause low oil pressure are either a bad pump or a bad bearing allowing the oil flow to squirt back into the oil pan.? ?If this is the case you will never build up pressure, its like having a leak in the garden hose.? ?

LOL,? Chet...

PS...? The pressures that you are reporting seem OK.? Different oil viscosity will affect the pressure at run.? Is your engine quiet or do you hear some bearing knock at high speed. ???

[30U sedan]

I'm worried that my oil pressure relief valve may not be working at all.......
How do I check it?

Thanks,

THIS IS THE GREATEST BOARD........

[30U sedan]

Pressure was around 40-45 lbs at start-up....... after engine warmed up it was around 30-40 lbs.

Now it is around 40-45 lbs at start-up...... after engine warms up it is around 20-30 lbs

[elmo]

What was your oil pressure before replacing the tubing , i havn't got a 30u hand book but do have one for a 29 dodge which i know is a 6 cyl   it says the oil pressure should be between 20-30 lbs at normal running speeds, the oil pressure for the later 36 on ply was only 30-45 lbs at normal runing speeds

[30U sedan]

Could you give more info on the pressure relief valve? My engine has had low oil pressure (20-30 lbs) since I replaced the bad copper tubing and replaced a leaking gasket on the oil pump.

I tried to adjust the relief valve but it seems to have no effect.

How does the valve work?

What do I need to do to reset it correctly?

Any ideas how to get the oil pressure back up?

[chetbrz]

Pat,

Thanks Pat, Yes I did mean those cars with the vacuum fuel system Q & U.  If these systems need to be adjusted it is most likely due to other issues within the engine?s oil system.   I guess the Plymouth people knew what they were talking about when they wrote the Plymouth Instruction Book.

Tks,  Chet?

[36 Ply]

Chet-

First of all, and most important, I hope that your engine is OK.

Secondly, thanks for posting the warning. I suspect that some folks would be too embarrassed to do so, fearing that it would invite criticism or ridicule. So thanks for clueing us all in to possible consequences.

Thirdly, is it your opinion that your warning would only apply to Plymouths with vacuum fuel pumps, or also to later Plymouths with mechanical fuel pumps (my Plymouth smarts, such as they are, don't go any earlier than 1936).

Thanks again for the warning, and good luck with your engine.

Regards,

Pat O'Connor

[chetbrz]

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...