oi pressure

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fishaman
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oi pressure

Postby fishaman » Wed Jan 28, 2015 3:37 pm

Hi, my name is Jim and i have a 1950 cub. When i start it, the oil pressure goes to 25 lbs. within 10 sec., but about one minute of running and you can watch the guage slowly drop off untill it is around 5 lbs of pressure. I put new oil gears and key in it. New .002 rods and mains, and new oil pressure relief valve with spring. none of this helped. I'm wondering if anyone has any answers or ideas where i might look next or what i can do to solve this problem. Thanks.

Bob McCarty
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Re: oi pressure

Postby Bob McCarty » Wed Jan 28, 2015 3:54 pm

Fishaman, Welcome to the Forum. I'm not an engine guy, but I'm sure someone will have some answers for you shortly.

Bob
"We don't need to think more,
we need to think differently."
-Albert Einstein

fishaman
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Re: oi pressure

Postby fishaman » Wed Jan 28, 2015 4:01 pm

Thanks Rob, I sure hope so cause it's driving me crazy.

tst
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Re: oi pressure

Postby tst » Wed Jan 28, 2015 4:11 pm

First I would put another oil pressure gauge on just to verify the gauge is working normally, after that your oil pressure is mostly controlled by the main bearing to crankshaft clearance, bearings wear down with old age causing to much clearance resulting in low oil pressure
good luck Tim

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Bill Hudson
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Re: oi pressure

Postby Bill Hudson » Wed Jan 28, 2015 4:45 pm

Since you worked on your oil pump, did you replace the oil pump gasket with an OEM gasket? In this application, gasket thickness is critical. Too thick a gasket allows some oil to bypass the pump gears, lowering oil pressure.

Bill
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fishaman
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Re: oi pressure

Postby fishaman » Wed Jan 28, 2015 5:59 pm

I did put a new oil guage on and i did use a OEM gasket on the oil pump. After i did all the work it pumped the same as before the work.

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Rick Spivey
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Re: oi pressure

Postby Rick Spivey » Wed Jan 28, 2015 6:05 pm

Since you said 0.002" main and rod bearings, I assume your crankshaft was at least mic'd or plastigaged, and maybe even ground? Could you tell us what condition the crank is in? Oil pressure is a function of the clearance in the pump, and in the bearing journals.....
Rick Spivey
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bob in CT
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Re: oi pressure

Postby bob in CT » Wed Jan 28, 2015 6:36 pm

Did you take out the oil gallery plugs? That one behind the timing gear has been forgotten before but I would not expect you would see the initial bump in pressure if that one was missing.
Did you lap down the pump body and gears as an assembly? They should be flush with the only clearance provided by the gasket. This is easily done by hand with some abrasive paper and a flat surface.

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Re: oi pressure

Postby Eugene » Wed Jan 28, 2015 7:47 pm

Something was missed during engine overhaul. Suggest pulling the engine and putting on the bench or engine stand.

Remeasure everything, double and triple check. My guess is the rod and main bearings are not correctly sized.
I have an excuse. CRS.

fishaman
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Re: oil pressure

Postby fishaman » Thu Jan 29, 2015 7:03 am

Thanks for all your input everyone, I really appreciate it. Something was definitely missed somewhere. The crank looked good and was miked before the new bearings were put on. I did not lap the oil pump and gears which is something I will do. I am going to pull the engine and recheck everything and find out where the problem is. Thanks again, Jim.


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