AMC 401 not holding oil pressure -

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post #1 of 7 Old 03-01-2009, 10:31 AM Thread Starter
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AMC 401 not holding oil pressure

I just replaced a 360 with a 401 in my cj7 but it won't hold very much oil pressure, below 10lbs at idle right now. Was wondering if this oil pressure is to be expected or if anyone has had this problem? also curious if anyone knows of where to find high volume oil pump? thanks

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post #2 of 7 Old 03-01-2009, 11:42 AM
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There is one advertised on AM Racing's site:

Spensive though.
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post #3 of 7 Old 03-01-2009, 11:48 AM
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Did you use the oil pump from the 360? If not, and you still have the 360, you might want to swap it over. My 401 idles at 30psi and holds at about 60psi at 2500 RPM. Good luck and let us know what you find out.

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post #4 of 7 Old 03-01-2009, 12:00 PM
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On my 360, I bought the pump gears from NAPA. I followed the assembly instructions, and at hot idle(650rpm) theres about 22psi, and anything over about 1500rpm, 58-60psi. This is with a fully warmed up motor, 90 degrees out, with Shell Rotella 15/40. I think my manual calls for 13 minimum, and 70 max, but I could be wrong.
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post #5 of 7 Old 03-01-2009, 02:30 PM
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IF the gauge is accurate and the oil pump bypass is working correct than I'd have to say you have bearing issues. I passed on several junkyard 360s in waggies that wouldn't hold oil pressure warm.

Did you pull the pan on the 401 and check a couple bearings before installing it?
Inspection kept me from installing a 360 that would have suffered the same fate once.

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post #6 of 7 Old 03-01-2009, 04:38 PM
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First thing I would do is make certain that the pressure gauge is giving the correct reading. A mechanical gauge is where I would start. I believe in checking the cheapest items first.

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post #7 of 7 Old 03-01-2009, 06:45 PM
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Originally Posted by wyocj View Post
I just replaced a 360 with a 401 in my cj7 but it won't hold very much oil pressure, below 10lbs at idle right now. Was wondering if this oil pressure is to be expected or if anyone has had this problem? also curious if anyone knows of where to find high volume oil pump? thanks
Depending on how your engine clearances are set up,
You should expect between 10 & 25 PSIG at idle.

Don't know what year engine you have, but if it is '86 or older, the pressure bypass will open around 65 PSIG, so don't expect much over that at any time.

AMC V-8 engines have the oil pump built into the front timing cover, and they are made of aluminum.
Being aluminum means they move around, open up clearances, and do strange things when they get cold/warm...

Bearing clearances aren't often the biggest problem,
Often times lifter bore clearances are the largest problem in the engine.
Lifters are 16 large 'Leaks' in an AMC engine, especially if the engine is '86 or older...

Cam bearings can be large losses too, but if you are going to tear down enough to take the cam bearings out,
Might as well do the mains/rods at the same time and plug up those leaks also!
Bearing shells are cheap and easy to install...

Anyway, just replacing the oil pump WITH THE CORRECT FLOOR PLATE GASKET will often make a large difference...
Consider a 'Mid Plate' for the oil pump floor plate/filter head component,
And don't forget to service the bypass spring/plunger when you have the bottom off the oil pump.
A sticking open bypass valve can cause some pretty bad problems...

Since all that is on the OUTSIDE of the engine/timing cover and easy to change, it's the 'Easiest' way to check/do things...
If that doesn't help, the worst you have done is set up a fresh oil pump for when your engine is rebuilt/refreshed...

High Pressure pumps for a stock AMC engine is a myth.
Since the oil pump body is cast right into the front cover, there is no way to increase the speed the pump turns, or it's displacement...

Your best bet is a tight, well fitting pump to the existing housing,
Swap for a housing that isn't eaten up (if that is the problem)...

There ARE some rotor/impeller designs out there SLIGHTLY more efficient at the same speed and in the same space restrictions,
But in the long run, the 'Gains' really won't help an engine bleeding to death internally...
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