Oil Pump Pressure

Cacti_Ken · Posted: Fri May 13, 2011 9:21 am Post subject: Oil Pump Pressure

How can I get more pressure out of the oil pump?

The oil filter in the circuit robs pressure from the bearings. Pressure is running like 25psi. I would like to have a little more. Seems to me that would be better.

My engine was rebuilt before installing. so all the stuff was in good order.

Or maybe better to block off the oil filter. But I know that would result in too much pressure. I put a guage on it before to measure it. Just wondering if I could up the pump pressure a little more.
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idiocrates · Posted: Fri May 13, 2011 10:49 am Post subject:

I think the oil pump on one of these jeeps is classified as a gear pump...right? If so....I think a gear pump is a positive displacement pump....and as such it will pump against whatever output resistance is available until either the bypass valve opens or a gasket fails somewhere. You could probably experiment with different bypass springs until the desired openning pressure is achieved. Did you apply the modification to the timing gear oiler at the front of the oil gallery? This mod reduces the size of the openning in the fitting which should increase the resistance to the flow and effectively increase the oil pressure (if the bypass doesn't open up first).
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'?? - M38A-1

madmike · Posted: Fri May 13, 2011 11:33 am Post subject:

I would like to know if this has been a problem since there appears to be a modification procedure. I am currently going thru my engine and if there is something I should do to increase durability, I would like to do it now. Since the military likely did not run these engines without oil filters, can I assume they are designed correctly and the modification is not a military solution? Maybe a solution for a weak pump or by pass-valve or some other problem?

Cacti_Ken · Posted: Fri May 13, 2011 12:52 pm Post subject:

idiocrates · Posted: Fri May 13, 2011 1:54 pm Post subject:

The modification I was referring to was given to me by Mr. Knettle.....he basically told me, if the no.1 journal was suffering from lack of proper oiling a usual fix was to replace the .070 orifice oil fitting at the front of the block with one that had a .040 orifice....or solder or braze the .070 orifice closed and redrill it to .040. As to which way to go with the spring....here's the rub.....at idle the relief valve isn't operative because the rpm of the engine and hence the volume of output oil and the resistance of the oil gallery are all in equilibrium. At high rpm during operation, the relief valve may or may not open and close due to the increased volume of oil output while the oil gallery resistance remains constant. What needs to be determined is exactly what the range of operating volumes are as the engine transitions from idle to full rpm. Then, if you know what the pressure resistance is of the entire oil gallery you should be able to find a spring that functions somewhere between the one you have now and the pressure that will blow open a gasket somewhere. I'm inclined to think this chore has already been done and the result is the spring that came installed in your oil pump. My experience with gear pumps come from a bunch of years fighting fires and using rural gear pump equipped fire trucks. Inferior or altered by-pass valves would almost always result in equipment damage if someone slammed a nozzle closed under full rpm. It became customeary practice to crack open a tank fill valve to parallel the by-pass valve "just in case" even if it meant slightly reduced volume and pressure at the nozzle. What the reduced orifice fitting does is increase the oil gallery resistance just enough to increase the oil pressure without endangering the integrity of the pump. And really....would you ever consider running an engine without an oil filter?
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Jim

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'?? - M38A-1

Cacti_Ken · Posted: Fri May 13, 2011 2:41 pm Post subject:

Where is this .070 orifice? I didn't rebuild my engine, someone else did.

Do you think the oil filter on these engines does much filtering?

I average 1000 miles per year. I could change the oil yearly.

But does the oil return from the oil filter housing have to be in place to oil anything up front?
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skyjeep50 · Member Joined: Feb 20, 2007 Posts: 606 Location: Illinois

The oil return line lubricates the camshaft drive chain - you don't want to lose that oil flow. You mention just 25 lbs oil pressure - when it is warmed up or cold? If the engine and oil is at operating pressure, 25 psi is not bad. And how are you determining the pressure, make sure your gauge is accurate.
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1951 M38

Cacti_Ken · Posted: Fri May 13, 2011 5:53 pm Post subject:

Check my photo gallery on page 3 for oil pressure test.
I had a new good gauge.

I said previously it was running like 25psi. It's a really almost 30 at high revs from the test I did awhile back. I was hoping to crank that up a little more and have at least 30 at idle.
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wesk · Posted: Fri May 13, 2011 10:17 pm Post subject:

This discussion has went on before Ken.

1-The oil jet for the cam gear was originally .070 on early L134's but was changed to .040 in the 50's. This was done to increase oil flow/pressure to the #1 rod bearing. The civvy manuals explain this.

2-The oil filter is a partial flow system which means not all the oil is directed through the filter on the same trip around the system. Filtering is a good thing no matter what system you use.

3-Try not to compare todays oil pressures (50 to 70 PSI) on todays very close tolerance bearings with the oil pressure (25 to 45) common to pre 1940 engine designs. They are not even close to each other.

4-The oil filter plays an important lubrication role on WWII engines with timing chains but that does not apply to this engine with timing gears. That .040 jet takes care of the gear oiling needs.

5-Where can your oil pressure go?
A-Excess bearing clearance.
B-Excess cam journal to cam bore clearance.
C-Worn lifter bodies and lifter bores.
D-Loose or missing internal oil gallery plugs and of course a loose or
missing timing gear oil jet.
E-Worn oil pump.
F-weak oil pressure relief valve spring.
G-Foreign particles holding relief valve off it's seat.
H-Loose rear cam journal welsh plug.

As you can see you have a lot of things to check for their correctness before you will need to consider modifying anything on the engine.

I'd start with a review of what actually was done during the overhaul and what used parts met what tolerances that were re-installed. You will want to know the precise dimensions that hopefully were properly recorded during the overhaul teardown and inspection. Things like the #2 & #3 cam journal bores were not equipped with bearings and once they exceed their max tolerance diameters the resulting low oil pressure is what you will see. Same goes for worn beyond allowable tolerance lifter bores. Ford 302 cam bearings can be fitted to the #2 and #3 cam journal bores to close that gap and there are oversized lifters available to fit those worn lifter bores.
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Wes K
45 MB, 51 M38, 54 M37, 66 M101A1, 60 CJ5, 76 DJ5D, 47Bantam T3-C & 5? M100

Mjeeps photo album: http://www.willysmjeeps.com/v2/modules.php?set_albumName=Wes-Knettle&op=modload&name=gallery&file=index&include=view_album.php

Cacti_Ken · Posted: Mon May 16, 2011 8:55 pm Post subject:

Sorry Wes I was too lazy to do a search. The engine rebuild was done eight years and 4000 miles back. A new oil pump was installed. Along with rebore and piston kit. Rod and journal brgs, and cam brgs. New valves and valve guides. I don't recall what else.

Your right I am comparing it to the pressure on modern engines. I really can't complain about the performance of it. The oil doesn't get black like it was doing during breakin period. So I'm leaving well enough alone.
About 5 gallons of gas used in 133 miles in overdrive ain't too bad.
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wesk · Posted: Mon May 16, 2011 10:44 pm Post subject:

26 miles per gallon is unheard of on the 4 banger Willys. What's your secret?
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Wes K
45 MB, 51 M38, 54 M37, 66 M101A1, 60 CJ5, 76 DJ5D, 47Bantam T3-C & 5? M100

Mjeeps photo album: http://www.willysmjeeps.com/v2/modules.php?set_albumName=Wes-Knettle&op=modload&name=gallery&file=index&include=view_album.php

maeserik · Posted: Tue May 17, 2011 12:19 am Post subject:

ken, do not worry about the oilpressure. A friend of mine has just 5 psi and 25 psi at full speed for several years on his CJ3a. The gauge is already replaced to be sure. The engine runs smooth, much power and no smoke or special noise...he said when there is oilpressue the lubrication in the bearings is OK. On my M38 i have about 25 on idle and on roadspeed the needle is at the end off the scale ( 60 psi gauge ). Or the sender or the gauge are not so good, but when i see the needdle moviing to the right there is oilpressue and thats the most important.

My M38 is now 5 years restored, and since that time once a year new oil and grease that is all what i have done. The only thing what i do not like is the noise the exchaust pipe makes ( resonation because no rubber components between pipe and frame )

i use 25W50 mineral oil
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1942 GPW 71336 my son's jeep restored now
1951 M38 MC11891
1953 VW beetle (genuine german Käfer )
1957 fantastic wife

http://www.surfacezero.com/g503/showgallery.php?cat=1865

and this webside

Cacti_Ken · Posted: Tue May 17, 2011 3:14 pm Post subject:

Yeah that does look way out in left field.

Sorry for the miscalculation, does make me look bad for sure. You must have thought this guy is lying out his axx.
It's more like 6.5 gal. I didn't include the 1.5 gallons I used to top it off at the end.
I stopped twice to go to rest room during the trip. I put gas back in each time.

1st stop put in 2.5 gal., 2nd stop put in 2.5 gal., at home put in 1.5 gal.
My odometer was 36091.0 on start and 36224.8 on return. 134miles and 6.5 gal.

I contribute the milage to the overdrive. I also had About 1.5 gal of 100 octane in it when I started out along with about an oz. of marvel mystery oil and a little lead substitute.

On another trip back in March I did 88 miles and use right at 4 gallons. I mostly did 40 & 45mph.
I checked the speed against my TomTom. The speed and odometer agree with the TomTom GPS.
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