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Rebuilt 3.0 low oil pressure

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Bfeils

Member
So I did a partial rebuild on a 3.0 where in I replaced the pistons, rings , connecting rod bearings, and crank bearings.

It seemed to be going pretty well good compression (185 on all cylinders) started right up, had some carb problems but a rebuild fixed that. I did a couple test runs at the lake to figure things out and was satisfied enough to take the family out. A couple hours into our trip I noticed the oil pressure waning. It had been around 40psi but was now hovering around 20 even dipping to 10 no matter the rpm. We cut the trip short because of that and a broken alternator belt.
Today I changed the oil and filter but it didn't seem to make a difference.
The pressure seems better cold at 35-40 but gets worse the longer it runs.

Anyone have any insights? I've never had an oil pressure problem in my vehicles so I'm not sure where to start.
 
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The oil pressure gauge relies on a variable potentiometer for it's signal..... (i.e., the sender unit)
It may be possible that the gauge or sender is bad.... or the circuit to the gauge has an issue.

Before assuming that the oil pump and/or something within the engine is bad, temporarily install a mechanical gauge as to verify actual pressure.
 
RicardoMarine said:
The oil pressure gauge relies on a variable potentiometer for it's signal..... (i.e., the sender unit)
It may be possible that the gauge or sender is bad.... or the circuit to the gauge has an issue.

Before assuming that the oil pump and/or something within the engine is bad, temporarily install a mechanical gauge as to verify actual pressure.
Click to expand...


Well I'm also getting some lifter noise when the pressure drops now that I ran it in the hose in my garage. Sadly I think it's more than a gauge issue.
 
So, this is interesting. I put half a can of sea foam in the crankcase and the pressure seems to have gone up. Now it's at about 35 at idle. Oddly, it doesn't go up much with throttle. Maybe 40psi at 2000rpm and then stays there.
Does anybody have any insight what that might indicate?

Edit to add... when i turn off the motor and give it five seconds and restart it the pressure is low for 5 seconds and then bounces right back up and stays there. If I throttle it up at all while its low I hear lifter rattles.
 
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So I'm a little hopeful now. I've let the sea foam sit for a day and now it seems to be pretty good. Maybe a stuck lifter for a few seconds after starting. Here's a video I made to show the behavior. You'll notice with headphones on that is a bit noisy after start but with a blip of throttle the pressure pops up another 5 or so psi and the noise goes away and doesn't come back.

Please give me your opinions. It runs beautifully I'd hate to tear it back down if it's not necessary.

https://youtu.be/_f0zLquaZFc
 
Just to update: all symptoms are gone. I believe I ran it too long without changing oil after the rebuild. I think the assembly lube was causing problems.
 
....or the spring loaded ball in the oil pump pressure regulator got stuck partially open with some crap that the seafoam cleared.
 
This is taking us back to July, but I have to ask...... what is a "partial rebuild"?

As for the oil pressure being low due to the assembly lube...... that would be highly unlikely!

As for hearing the rattle...... how did you make the initial cam follower "plunger" depth adjustment?


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Partial rebuild meaning the engine had two with stuck piston rings so I replaced the pistons, rings, crank and rod bearings. Never took the cam out. Cylinder walls still had factory cross hatch so I didn't machine anything. I adjusted the valves per the service manual. I think the noise was one or more lifters not pumping up reliably when the pressure was low.
 
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Bfeils said:
Partial rebuild meaning the engine had two with stuck piston rings so I replaced the pistons, rings, crank and rod bearings. Never took the cam out. Cylinder walls still had factory cross hatch so I didn't machine anything.
OK.... thank you for clarifying that!

I adjusted the valves per the service manual.
Service manuals often suggest setting more than one cylinder's cam followers (aka lifters) per crank position.
You will do much better if you adjust for one cylinder at a time.

Example:
Bring #1 cylinder around to TDC C/S (C/S = compression stroke)
This places those two cam lobes at the bottom of base circle.

Now adjust both Intake and Exhaust cam followers by first adjusting for ZERO rocker arm/valve stem lash.
Next, further tighten the rocker arm nut to OEM spec as to set the cam follower's plunger depth.
(the plunger depth is what we are actually adjusting for...... not any valve adjustment)

Since this is a 4 cylinder engine, (360 Xs 2 = 720 divided by 4 = 180) now roll the crank around 180* to #3 cylinder @ TDC C/S.
Make the same adjustment as you did to #1.

The firing order is 1-3-4-2, so the next cylinder in line will be #4.
Do the same to each cylinder until you finish up with #2.

I think the noise was one or more lifters not pumping up reliably when the pressure was low.
The oil pressure within a cam follower chamber remains ambient until the camshaft actually begins to operate the valve.
Once the cam lobe begins to move the valve from it's seat, the pressure underneath the plunger increases due to the work load.
In other words, it is the "trapped" oil within the follower that holds the plunger's position during valve operation.
Once the valve has been operated (opened and closed), the pressure beneath the plunger returns to ambient.
Click to expand...



Here's a neat little GIF file that shows us the actual operation of a hydraulic cam follower (aka tappet, lifter, etc).
Use the pause button so that you can read the text at the right side.

It begins with no oil of which allows the plunger to move freely and to bottom out.
As oil enters the chamber, all lash is eliminated and the plunger begins to work hydraulically.
(read text at 9 seconds into the video)


https://www.youtube.com/watch?v=lorANZ1Tptw



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Thanks, that's good info. Yeah the way the manual has you do it is top dead center on one cylinder and you set 5 valves and then on another cylinder the other three. I don't remember the exact procedure though.
 
I just use the screw driver method! Put your finger in the #1 plug hole and turn the crank until you feel compression the stick a skinny screwdriver in the hole turn the crank until the piston in all the way up. Adjust those rockers then just follow the firing order with the screwdriver.
 
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Bfeils said:
Thanks, that's good info. Yeah the way the manual has you do it is top dead center on one cylinder and you set 5 valves and then on another cylinder the other three. I don't remember the exact procedure though.

In many circles, this is known as the "cheater" method. It is used by those who want a short-cut.
I find it hard to believe that an Engineer would actually recommend using it when the 8, 6 or 4 stop procedure is so simlpe and easy! :mad:
Click to expand...

kimcrwbr1 said:
I just use the screw driver method! Put your finger in the #1 plug hole and turn the crank until you feel compression the stick a skinny screwdriver in the hole turn the crank until the piston in all the way up. Adjust those rockers then just follow the firing order with the screwdriver.

Easy/cheesy once TDC C/S has been established.

A 4 cycle engine passes all cylinders through complete cycles in 720* of crankshaft rotation.
Divide 720* by the number of cylinders.

Bring #1 around to TDC C/S.

On a V-8, mark the balancer off in increments of 90* (a white paint pen works well)
Adjust #1, roll crank around to the next marking, and adjust the next cylinder in the firing order.

On a 6 cylinder, mark the balancer off in increments of 120*.
Adjust #1, roll crank around to the next marking, and adjust the next cylinder in the firing order.

On a 4 cylinder, mark the balancer off in increments of 180*.
Adjust #1, roll crank around to the next marking, and adjust the next cylinder in the firing order.

These are known as the 8 stop, 6 stop and 4 stop procedures.
Use this procedure, and you won't need to go back through them dynamically.
Click to expand...



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