Not my first rodeo. Was a machinist for many years and have built many motors. Inside mics and outside mics, dial indicator for thrust, feeler gauges for side clearance on rods. No snap gauges or plastigage (except for verification). All plugs appear to be in place and there was great oil flow to the heads when I spun up the oil pump. I am relatively new to LA motors, so certainly don't know everything - the little quirks and fixes and that sort of thing. Like it took me a minute to figure out only one head at a time gets oiled - till I rolled the motor over and got oil to the other side! So......pretty certain the clearances are right. I coulda missed something I suppose, but between me and the guy I work with we have at least 60 years experience. It could still happen tho. Thanks for your input!
low oil pressure
- Thread starter DARTLARRY
- Start date
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nm9stheham
Well-Known Member
Stock pickup? If so, then it can set on the bottom of the pan and be OK; it draws through the side opening, not the bottom.
Can you share some actual pressure readings? 45-55 psi stone cold at low idle would be possible for the lower pump spring pressure.
Standard main bearings with groove on the top half only? Actual bearing clearances that were set/found? We're just checking everything but can't do that without actual info provided by you.
And there are plugs on the front and rear of the 2 oil galleries that can get left out. The one in front of the distributor shaft is the most common to get left out but the 2 in front are also forgotten with varying results.
The filter bypass or drain back are not at all likely.
Did you use ARP main studs by any chance? They are problematic for jacking up one side of the oil pump mounting to the rear main cap.
Can you share some actual pressure readings? 45-55 psi stone cold at low idle would be possible for the lower pump spring pressure.
Standard main bearings with groove on the top half only? Actual bearing clearances that were set/found? We're just checking everything but can't do that without actual info provided by you.
And there are plugs on the front and rear of the 2 oil galleries that can get left out. The one in front of the distributor shaft is the most common to get left out but the 2 in front are also forgotten with varying results.
The filter bypass or drain back are not at all likely.
Did you use ARP main studs by any chance? They are problematic for jacking up one side of the oil pump mounting to the rear main cap.
furrystump
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Oil plug under the oil pressure sending unit?
The oil pressure stone cold (does not idle low cold - big cam and a bit balky when cold ) runs about 45-55+ blip the throttle and it goes up just a few pounds to just under 60# (probably the low press spring 57#) As it heats up, the pressure gradually falls to around 10# at idle (1150 rpm in neutral)
Cruising down the road at about 60 it is running ~ 25#. (No tach in the car just yet - trying to find a good tach and inconspicuous place to mount it. Trying for a relatively stock appearance.) 24" tires and 3.23 gears.
ARP bolts - not studs. Will double check the seating of the oil pump flange when I remove the motor (been tied up with other projects)
Good to know about the pickup - didn't really give it a good look - was more concerned with the windage tray.
I will check on the clearances, but they were well within spec and - to be honest, I do not remember the type mains I put in - I will look that up when I get to the shop - but believe they were the top half grooved stock type bearings. Cleveite P perhaps?
Thank you for your input!
RT
25 years racing, a dozen or so race cars, 5 championships and more also rans than I care to think about!
DARTLARRY
Well-Known Member
update: pulled intake to check lifters, in doing so i stripped out 2 intake bolts. I had a fresh set of heads on the bench, so i just swapped them. I didn't change cam, lifters look fine, just changed heads. I now have 40psi of oil pressure when warm, this makes no sense to me.
nm9stheham
Well-Known Member
You're right... does not compute.
- Did you touch the distributor or intermediate shaft during this process?
DARTLARRY
Well-Known Member
I am leaning towards cam bearings now, It still has a tick when cold.
Not sure if you fixed your issue and this is an old thread but I’m researching because my motor does the same thing with a new standard melling72 pump. Could be the lifters/push rods. I have the comp cam amc style lifters that came with my xe256 cam kit using the stock stamp steel rockers and 7.5” push rods non oil thru and what’s happening as I understand it there’s not enough preload on the lifters to block that oil bleeding from the lifter cup when the engine gets hot. So I may go to a 7.550” push rod to see if that makes a difference. Apparently the newer AMC lifters are .020 smaller in the cup area than the stock style, check your preload before tearing your engine apart might be a simple fix worth checking it out.
DARTLARRY
Well-Known Member
I replaced the oil pump, with a new Melling 72, it has plenty of pressure now.
still has a tick in the valvetrain, i may need to check the pushrod length.
still has a tick in the valvetrain, i may need to check the pushrod length.
nm9stheham
Well-Known Member
Interesting... sometimes those little quirky things show up. Never thought of that one....
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