Oil pressure relief valve experiment

Ok so I rebuilt my engine in my 49 8n about 10 year ago. I did not do the oil pump I know I should have but I just didn't so thats that. I didn't replace my oil pressure relief valve and spring either. Just like most everyone else I have 30 lbs cold and around 10 hot.

I got my new spring and plunger today so I takes the old one out and on visual inspection they are both the same length but the old one seems to be a thinner steal so i gave it the squeeze test. hmm much lighter. so I got out the wife's kitchen scale and with the old spring and plunger it took about 3 lbs to compress it until the plunger bottomed out on the scale. interesting Hmmm.

the new spring and old plunger( I used the old plunger in the test so the spring was the only difference) it topped out the scale and still had room to go. I think the scale tops out at 5 lbs. So it probably takes 6 or 7 lbs to compress the new one down.

Well that got me thinking I wonder if the tension n the old spring changes when it heats up, I figured I would spare the wife's scale from the melty circles caused by my silly experiments. I am going to say that weather or not it does is irrelevant because it was bad eithr way. It will be a week or 2 before I get it all back together(paint, rewiring general cleaning). what do you think the chances are that I start to see 40 lbs cold and 20 or better hot once its all back together and what is your experience with oil pressure and the relief valve?

The aftermarket sprangs are stiffer and would be a issue on a engine in top notch condition...

I will wager your stiffer sprang will make little to no difference if all the pressure it can make cold is 30...

Thanks for the reply Hobo. I can understand what your saying, your probably right. I was hoping it may make a little more when hot. wishful thinking maybe.
I thought I read in the F0-4 one time that there is a specific amount of pressure to compress the spring I cant seem to find it now and it may be irrelevant anyway. Thanks for stopping by. I probably should have just rebuilt the oil pump when I had it apart however many year ago that was. I think I may be a little wiser than I was back then now too so maybe its best I waited.

Since you are compressing the two springs the same amount you are measuring the spring rate. The spring rate is proportional to the wire diameter to the four power. You stated the old spring is the same length; if the out side diameter and the number of active coils is also the same for both springs then the difference you noted is due to the wire diameter.

A spring can take a set over time however, the spring rate does not change. The old spring could have been longer (more space between the coils) when it was new, in which case you would be compressing it a greater distance resulting in more force.

The operating oil temperature would not have a significate effect on the spring.

Finally - if the pumps output is not great enough to cause the relief valve to open then adding more spring pressure to hold it closed will not change the oil pressure.

very helpful input. sounds pretty thorough. thanks for stopping by.

i agree with hobo , i had an issue with oil pressure problem that i posted a couple weeks ago . after rebuilding the pump still no pressure , it was a home made relief valve . but my thinking is that if the spring is week there is not enough force to keep the plunger in place to create pressure . my case was the parts were to short . i dont want to beat a dead horse but if i ever have oil pressure problems again the valve will be checked before i do anything . one more note , an older tractor repair guy told me some people put washers behind the spring to increase pressure.
thanks

I remember reading the threads you posted about the problem you had. Springs n Things do wear out. It doesn't seem too far fetched that after 67 years of service a spring might wear out. Maybe not. It wont do no harm to just put that new spring in there. may not help much either but im wiling to take the chance. if it does help yer dern tootn im gonna let yall know about it dern good chance i'll let ya know if it doesn't do nothin either

Hobo,
Why would the stiffer springs be an issue on a "in top notch engine"? what would explain that statement? I am a little confused by it
I am not sure I understand anymore.

shownuff........coil springs don't wear out. You want more oil pressure on a 20% accurate gauge? Change yer 6-qts of oil to HEAVER oil. Modern multi-vis oil ....ie.... 10-30 is 10wt oil that acts like 30wt oil when HOT. In 1939, Ford specified 30wt detergent oil. 40wt in HOT summer climate. Yer oil pressure is a function of engine bearing clearances and oil viscosity and yer spring loaded pop-off valve. I'd change to 40wt detergent, or even 50wt oil. ......oily Dell

(quoted from post at 21:04:40 05/07/15) Ok so I rebuilt my engine in my 49 8n about 10 year ago. I did not do the oil pump I know I should have but I just didn't so thats that. I didn't replace my oil pressure relief valve and spring either. Just like most everyone else I have 30 lbs cold and around 10 hot.

I got my new spring and plunger today so I takes the old one out and on visual inspection they are both the same length but the old one seems to be a thinner steal so i gave it the squeeze test. hmm much lighter. so I got out the wife's kitchen scale and with the old spring and plunger it took about 3 lbs to compress it until the plunger bottomed out on the scale. interesting Hmmm.

the new spring and old plunger( I used the old plunger in the test so the spring was the only difference) it topped out the scale and still had room to go. I think the scale tops out at 5 lbs. So it probably takes 6 or 7 lbs to compress the new one down.

Well that got me thinking I wonder if the tension n the old spring changes when it heats up, I figured I would spare the wife's scale from the melty circles caused by my silly experiments. I am going to say that weather or not it does is irrelevant because it was bad eithr way. It will be a week or 2 before I get it all back together(paint, rewiring general cleaning). what do you think the chances are that I start to see 40 lbs cold and 20 or better hot once its all back together and what is your experience with oil pressure and the relief valve?

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The oil pressure relief valve is a pressure limiter not a pressure regulator. It stays on it's seat until oil pressure rises to the engineered relief pressure (generally believed to be about 45-50 PSI) at which point it opens enough to prevent the pressure from going any higher. Increasing the spring tension (valve cracking pressure) will increase the relief pressure setting but do nothing at oil pressures below the old relief setting.

The Ford tension specification for the relief valve spring (taken from the 120 CID industrial engine manual) is 44-46 ounces at a compressed length of 1.40 inches. As long as the spring has that tension at that length it is working correctly. The manual is quite specific - replace the spring if it is [b:7104130cca][u:7104130cca]less than[/u:7104130cca] [/b:7104130cca]or [b:7104130cca][u:7104130cca]greater than[/u:7104130cca][/b:7104130cca] those numbers. You have a scale and a ruler....

TOH

Arrrg!!!!!! Duplicate post deleted.....

(quoted from post at 11:41:25 05/08/15) shownuff........coil springs don't wear out. You want more oil pressure on a 20% accurate gauge? Change yer 6-qts of oil to HEAVER oil. Modern multi-vis oil ....ie.... 10-30 is 10wt oil that acts like 30wt oil when HOT. In 1939, Ford specified 30wt detergent oil. 40wt in HOT summer climate. Yer oil pressure is a function of engine bearing clearances and oil viscosity and yer spring loaded pop-off valve. I'd change to 40wt detergent, or even 50wt oil. ......oily Dell

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The do ware the ware comes from the valve riding/sliding inside the spring...

(quoted from post at 07:26:36 05/08/15)

(quoted from post at 11:41:25 05/08/15) shownuff........coil springs don't wear out. You want more oil pressure on a 20% accurate gauge? Change yer 6-qts of oil to HEAVER oil. Modern multi-vis oil ....ie.... 10-30 is 10wt oil that acts like 30wt oil when HOT. In 1939, Ford specified 30wt detergent oil. 40wt in HOT summer climate. Yer oil pressure is a function of engine bearing clearances and oil viscosity and yer spring loaded pop-off valve. I'd change to 40wt detergent, or even 50wt oil. ......oily Dell

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The do ware the ware comes from the valve riding/sliding inside the spring...

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Repeated cycling of a spring will cause metal fatigue and loss of tension - no mechanical wear required. Heating and cooling cycles do that as well. Springs have a design service life and do wear out.

TOH

My #1 reason would be overworking the oil pump and causing premature pump ware...

A N engine in excellent condition can easily make 100 psi unregulated... With a stiffer spring the pressure has a hammer effect the pressure will buzz/bounce a good test gauge tho your cheap gauge will show a steady reading...

You can google "is too much oil pressure bad" and make up your own mine....

Making to much OP is not a bad issue to have on a N because its EZ to overcome... I had rather know I can make more than cannot... This is one part I want OEM not a so called original knock off...

after further inspection I see that on the outside of the spring at about the third and starting on the 4th coil down
there is a shiny spot where it was rubbing against something causing a flat spot. That tells me that it was not
staying on its seat, it was moving, at a lower pressure than required. So I measured it and compressed it and got
about 32 oz. at 1.4 inches. I think we are making progress now.

Springs do have a service life and do wear out. If the spring is worn out and breaking its seat at, we'll say about
35 lbs just as an example so now this worn spring is not relieving excessive pressure it is in a way regulating it
because it breaks its seal to soon letting that pressure leak past and keeping it from operating as it should. Does
that make sense. I think telling people that it doesn't wear out is a bad road to go down.

(quoted from post at 09:58:28 05/08/15) after further inspection I see that on the outside of the spring at about the third and starting on the 4th coil down
there is a shiny spot where it was rubbing against something causing a flat spot. That tells me that it was not
staying on its seat, it was moving, at a lower pressure than required. So I measured it and compressed it and got
about 32 oz. at 1.4 inches. I think we are making progress now.

Springs do have a service life and do wear out. If the spring is worn out and breaking its seat at, we'll say about
35 lbs just as an example so now this worn spring is not relieving excessive pressure it is in a way regulating it
because it breaks its seal to soon letting that pressure leak past and keeping it from operating as it should. Does
that make sense. I think telling people that it doesn't wear out is a bad road to go down.

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o "H" with all the theorizing & technical "reasoning" here............it is NOT your relief valve/spring that causes a drop from 30 to 10 PSI as engine warms up. Furthermore, on the big IF that a new spring brings it up to 40 cold, my case of beer says it will still drop to 10 hot.

My #1 reason would be overworking the oil pump and causing premature pump ware...

A N engine in excellent condition can easily make 100 psi unregulated...

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I have a over worn N motor that would start with no oil pressure . A few seconds after it started you could hear the motor lug down as the oil pressure kicked in .

I have heard , but not confirmed that a small block v8 uses 5 horsepower to turn the oil pump at a normal load . The topic I was reading was bronze gears and high volume oil pumps vs motor ware .

High oil pressure sounds good and has it's bragging rites I recon , but but you will pay for it in oil pump ware and horsepower consumption .

In my unscientific opinion anything over 30 psi is costing you .

(quoted from post at 09:58:28 05/08/15) after further inspection I see that on the outside of the spring at about the third and starting on the 4th coil down
there is a shiny spot where it was rubbing against something causing a flat spot. That tells me that it was not
staying on its seat, it was moving, at a lower pressure than required. So I measured it and compressed it and got
about 32 oz. at 1.4 inches. I think we are making progress now.

Springs do have a service life and do wear out. If the spring is worn out and breaking its seat at, we'll say about
35 lbs just as an example so now this worn spring is not relieving excessive pressure it is in a way regulating it
because it breaks its seal to soon letting that pressure leak past and keeping it from operating as it should. Does
that make sense. I think telling people that it doesn't wear out is a bad road to go down.

Click to expand...

You are tilting at windmills. The spring is not the cause of your 30 PSI cold/10 PSI hot oil pressure. The cause is excessive oil clearances and/or insufficient volume from the oil pump.

TOH

you are probably right and it may not be anything at all, I am fine with it only having 10 lbs.

It sure is a fact that the old spring is worn and is going to be replaced.
By the looks of the shiny flattened wear mark on the spring it must have been moving, it didn't get that way from
staying still and if it was moving then its quite possible that the plunger was loosing its seat. If its loosing
its seat and im only making 30 lbs it isn't working properly, further down the road that could be why the timing
cover is gunked up with a coating of dirt and oil.

I had a guy build a ramp for me the center support was 1.5 inches too long so it held the decking up a bit. he
gnawed away at the top of the 2x8 support to lower the board so it hit the other supports without that hump in it.
then a couple decking boards were to short so he put some 2x8 in there and pieced all the decking together on top
of that. it was solid and would work, all the decking was at different heights, the bottom two boards were a 2x4
and a 2x8 with an angle gnawed into it. Looked like heck. it would work but was it right? that's kinda where I am
at with this spring, it would work but was it correct?

This isn't really about raising oil pressure but more about the operation of a part. Ive never had more than 30lbs
of pressure so there should be no wear on the spring it should never compress but it has. I'm not sure I would go
around telling people springs don't wear out, maybe they wear in. I appreciate all the replies and discussion. I'm
just going to move along.

(quoted from post at 13:44:43 05/08/15) you are probably right and it may not be anything at all, I am fine with it only having 10 lbs.

<snip>

This isn't really about raising oil pressure but more about the operation of a part. Ive never had more than 30lbs
of pressure so there should be no wear on the spring [b:5ddda7f0a4][u:5ddda7f0a4]it should never compress but it has[/u:5ddda7f0a4][/b:5ddda7f0a4].

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It is designed to compress every time you start a cold engine. That is why it is in the system - it compresses and relieves cold oil pressure. If it didn't it would be worthless. What makes you think the wear marks didn't occur BEFORE your engine was worn to the point that the cold oil pressure never hit 45+ PSI and cracked the valve? After all it's only been 50 odd years. You have the specifications - use them.

TOH

When I bought my 9n. It also had low oil pressure hot. And like you I checked the plunger and spring. I found someone had ground a
large grove in the plunger. I replaced the spring and plunger. I might have gained 3-4 pounds of pressure. (don't really remember)

Thinking the pump was bad I tore my 9n down. The pump was nice and tight. Digging deeper in the engine. I found the main bearings
to be loose. The machine shop ground my crank 20 under. They said my pump couldn't be any tighter even if it was rebuilt. The pump
was left as is. Put in new bearings and rings. It now has 60 pounds hot or cold.

I'm not speaking for Hobo, but I believe what he meant by "top notch" was an engine without clearance wear or a new engine. A stiffer spring would mean higher than normal pressure and that isn't good. I have seen oil filters balloon and heard of them being blown off.

put an OEM spring and plunger in.
Check its seat for mars or burrs.
run it
your oil pressure after 2 hours of work on a warm day..
....is your oil pressure.
Nothing you do up front will change that.
Gotta go into the engine to fix that.
Heavy oil will gain you only a little time, and maybe a lb or two on that warm day.
(change the 50w oil in your Harley after some riding on a 90 degree day.....hey what happened to my 50w....this looks like brown water lol)

like to add, [i:ef589d5ef8]sudden[/i:ef589d5ef8] changes always need a look.
had a JD 2-cyl that suddenly had half its normal oil pressure.
A small piece of debris got stuck under the relief plunger and was holding it off its seat.

(reply to post at 08:54:43 05/09/15)

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The tip of the plunger is spose to have a flat spot its a built in leak to supply the cam gear lube...

Given that I have a 2N that needs a rebuild (oil pressure problems), I decided replacing the plunger and spring would be an interesting experiment.

Fresh 15W-40 oil with a bottle of STP for good measure (tried this before this experiment).

Before:
Cold Idle - 15 psi
Cold Full Throttle - 20 psi
Hot Full Throttle - 0 psi

After:
Cold Idle - 45 psi
Cold Full Throttle - 50 psi (not sure if the gauge was pegged)
Hot Idle - 0 psi
Hot Full Throttle - 2 psi

Maybe it would have helped prolong the engine life if it had been done earlier, but it's not going to work this time. I see a rebuild in the future.

Coincidentally, just saw an 8N with ROPS that I'm going to take a closer look at. Looks pretty clean, but only showed 10 psi of oil pressure at idle. Going to see if it drops much as it warms up. Hoping not as it's nice otherwise.