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Chillin with the top off.
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4,891 Posts
Discussion Starter #1 (Edited)
I have a cj7 with a rebuilt 390 amc v8. Runs like a raped ape.. Ok, Now on to the problem.. It has 50# oil pressure at start up, when it warms up it has 5.. If I rev it above 1250rpm the oil pressure comes back to 15-20 lbs.. I changed from 10w/30 to 20w/50 and it helped a little.. I ordered a oil pump kit and am going to try that tomorrow.. The engine was rebuilt approx. 20,000 miles ago and does not smoke and runs great.. I saw recipts from rebuild and am floored what it could be.. Any ideas? Thankx
 

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Chillin with the top off.
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4,891 Posts
Discussion Starter #2
I just pulled the pan and the pan and screen are clean..
Pulling the oil pump apart now..
 

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Chillin with the top off.
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4,891 Posts
Discussion Starter #4
Mechanical guage... Brand new..
I just pulled the oil pump apart and the front cover looks worn pretty good.. I think I found the culprit..
 

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Chillin with the top off.
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4,891 Posts
Discussion Starter #5
Bump. Back again. Bought a oil pump wear plate and installed it still very low pressure..
 

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Registered
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2,153 Posts
Only thing left would be a slipped bearing (that I can think of) or plugged oil filter. What was the warranty on the rebuild?
 

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Resident HVAC/R Jambi
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10,939 Posts
Did you change your filter and oil? I had no pressure, and it was a plugged filter (I have a plugged filter bypass so a bad filiter = no pressure).

Otherwise, did you check your high pressure spring and plunger?
 

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Premium Member
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4,651 Posts
mains are gone. after the oil warms up and thins out, there is too much clearance between the crank and main bearings to hold good oil pressure
#1 most likely.

Plastigage it.
 

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rapid city recovery team
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1,049 Posts
if the spring in oil pump is worn out it will cause the same problem. I have a 360 that does the samething. Replace that spring before you start pulling the crank.
 

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Premium Member
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Thge pan is already off, and he doesn't have to pull the crank to plastigage it.

I'm betting on worn mains.
 

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Chillin with the top off.
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4,891 Posts
Discussion Starter #16
OK here it what i did so far..
New mechanical guage.
Dropped pan and checked screen
Rebuilt oil pump with new gears and spring and plunger
Rebuilt oil pump with new wear plate.
Changed out timing cover with a known good one off of a 304.
Drank lots of beer and scratched my head..


I have 5-10psi at idle and 40 at 2000 rpms.. Motor runs awesome lots of torque just bad oil pressure.. I guess I will just pull it and put in another bullet..
 

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Premium Member
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4,651 Posts
Just run it if you aren't going to check anything else. 10lb/1,000 RpM is fine, and you get better than that at 2,000. I ran a MoPar 360 in my Scrambler for 3 years with barely any oil pressure at idle....
 

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Chillin with the top off.
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4,891 Posts
Discussion Starter #18
Just run it if you aren't going to check anything else. 10lb/1,000 RpM is fine, and you get better than that at 2,000. I ran a MoPar 360 in my Scrambler for 3 years with barely any oil pressure at idle....
I would but it has fresh pistons cam and everything else.. Plus at idle I can hear a little man knocking on the side of the oil pan..:tonka:
 

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Chillin with the top off.
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4,891 Posts
Discussion Starter #19
It just went so fast. Good oil pressure to no oil pressure..
 
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