Low Oil Pressure

Nov. 18, 1941 - MB100001 thru Mar. 6, 1942 - MB125809 NO EBAY or COMMERCIAL SALES.
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tizzard
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Low Oil Pressure

Post by tizzard » Sat Aug 13, 2022 8:51 am

Hi

Having had lots of WW2 Jeeps over the intervening years I am fully conversant with the oil pressure expectations of a Jeep (MB) when warm and cold on both tick over and when being driven. My Slat Grill has just been the subject of a reasonably extension and sympathetic restoration of in the main bodywork. When the sump was off the engineer checked the bearings etc, and declared them good with no noticeable wear. In fairness, even when very hot the engine sounds really sweet whether on tick over or when being revved. However, now that it has been driven for a while I am concerned about continuing very low oil pressure levels especially when on tick over (2-5lbs). I have flushed the engine, changed the oil and filter etc, all to no avail. At around 30MPH with an engine temperature of approximately 150c it returns around 40lbs per sq. inch, it will when being revved increase to around 60lbs but when on overrun the pressure quickly drops to around 20lbs and is a little sluggish returning to 40lbs. I would say overall the oil pressure response by gauge reading is slow.

To reiterate - it sounds sweet whatever the oil pressure with no knocks nor rumblings.

Thoughts please.

Thanks

Andy
Willys Slat Grill 123045. Body No.23765. DoD 3 - 25 - 42 .ARN No. 79545
1939 Royal Enfield WD/C 350cc solo motorcycle


mugginsmoo
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Re: Low Oil Pressure

Post by mugginsmoo » Sat Aug 13, 2022 4:36 pm

silly question but
have you tried fitting a different gauge?
personally that would be the first thing I would try, and to add I would put it straight into the block where the line to the factory gauge goes.
by doing this you are isolating the issue down to the gauge, its hard line and (where I suspect the issue is) the flexible line.
if you try to fail and succeed, what have you done?

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tizzard
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Re: Low Oil Pressure

Post by tizzard » Sun Aug 14, 2022 9:33 am

Thanks for that. I had been considering the idea but I think you are right, the investment in a repro gauge would be worthwhile :D
Willys Slat Grill 123045. Body No.23765. DoD 3 - 25 - 42 .ARN No. 79545
1939 Royal Enfield WD/C 350cc solo motorcycle

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Re: Low Oil Pressure

Post by parker007 » Sun Aug 14, 2022 12:15 pm

first 20 psi hot at idle i would not be to worried. if 10 or below better do something now. if your worried i would try a new melling oil pump, but change the oil to quality oil first.if a good pump and good oil and still low your bearings need attention.

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tizzard
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Re: Low Oil Pressure

Post by tizzard » Wed Aug 17, 2022 9:12 am

Thanks for your assistance. Are there any pitfalls in changing the oil pump?
Willys Slat Grill 123045. Body No.23765. DoD 3 - 25 - 42 .ARN No. 79545
1939 Royal Enfield WD/C 350cc solo motorcycle

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Re: Low Oil Pressure

Post by parker007 » Wed Aug 17, 2022 3:44 pm

pretty basic, just make sure you clock the gear in the correct place and then you have to start over with the distributor timing.

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tizzard
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Re: Low Oil Pressure

Post by tizzard » Fri Aug 19, 2022 5:53 am

Thanks :D
Willys Slat Grill 123045. Body No.23765. DoD 3 - 25 - 42 .ARN No. 79545
1939 Royal Enfield WD/C 350cc solo motorcycle

dinof
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Re: Low Oil Pressure

Post by dinof » Sat Aug 27, 2022 3:46 pm

Do not install oil pump dry. Fill all holes and even twirl the rod around to pull as much oil in as you can.
Use a straight weight 30wt. oil. That was the original weight used back then but will you help gauge
the pressure on the gauge.

How is the fuel pump? Mine was about 13 years old from my rebuild, but it was letting a little bit of
gas into the crankcase, diluting the oil thus lowering the pressure. Yes, it happens.
Dino Falabrino
On the "G" since 1998.
1943 GPW 102310 DOD 3-3-43
1928 Model A Roadster Pickup
1930 Model A Tudor
1968 Taco Minibike

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Re: Low Oil Pressure

Post by YLG80 » Sat Aug 27, 2022 9:52 pm

Hi Andy,
Did you check the little hole in the oil filter? It needs to have the correct diameter.
Sometimes it get bigger due the to the edges rusting or being enlarged when trying to unplug it
In that L4 engine, the oil pressure is determined by the oil flow through restrictions, i.e bearings, oil galleries, oil filter hole etc..

The flow rate is equal to the velocity multiplied by the cross section.
At idle speed, for a given cross section, the flow rate will be lower as well as the displayed pressure which is proportional to the flow rate. :wink:

The little hole calculated value (Tony Norton) is 0.055’’. Do never enlarge that hole.
See here: viewtopic.php?p=1791081#p1791081
The Tony Norton explanation is given down to the linked picture.
Yves
Last edited by YLG80 on Sat Aug 27, 2022 10:15 pm, edited 1 time in total.
Ford GPW 1943 - Louisville - DoD 12-7-43
serial 164794

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Re: Low Oil Pressure

Post by YLG80 » Sat Aug 27, 2022 10:14 pm

Here is the oil filter drawing with the hole dimensions :

THF405269_GPW-18660_WO-A-1230_OIL_FILTER_AND_BRACKET_ASSY.jpg

Tony Norton was correct in his calculation base on the bearings gaps.
Yves
Ford GPW 1943 - Louisville - DoD 12-7-43
serial 164794

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tizzard
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Re: Low Oil Pressure

Post by tizzard » Sun Aug 28, 2022 7:27 am

Phew! :shock: Thanks :D
Willys Slat Grill 123045. Body No.23765. DoD 3 - 25 - 42 .ARN No. 79545
1939 Royal Enfield WD/C 350cc solo motorcycle


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