88 4.2 I6 LOW oil pressure

[wrangler rider]

I just rebuilt a 88 I6 AMC 258 i6 / 4.2l its 6thous over and crank is 2 thou under, just put new rings in yesterday (did 2 rebuilds 1 with wrong rings), i replaced the sending unit with a mechanical one and put in a new oil pump between rebuilds, now it starts up with 20 to 40lbs and when its hot i have between 5-0 gauge doesnt read it, screen is clean ran a old oil filter after rebuild and replaced it after 30mins of running

so what should i do? could the oil pump go bad that fast? or am i missing somethin?

it was about 100 miles between rebuilds also its a 5spd jeep

 

[Cheepjeep85]

Did you put new bearings in the bottom end, when you built it the first time did you put new cam bearings in? There are several things it could be. I wouldn't suspect the oil pump first off, if its new. Did the wrong size rings do any damage to the motor, like send a bunch of shavings through it. You say the crank was reground to 0.002, do you have the correct bearings in it. And did you make sure the rod and main caps were retorqued to the correct specs.

Drooooid...2

 

[wrangler rider]

Did you put new bearings in the bottom end, when you built it the first time did you put new cam bearings in? There are several things it could be. I wouldn't suspect the oil pump first off, if its new. Did the wrong size rings do any damage to the motor, like send a bunch of shavings through it. You say the crank was reground to 0.002, do you have the correct bearings in it. And did you make sure the rod and main caps were retorqued to the correct specs.

Drooooid...2

no shavings, didnt need cam bearing, new rod bearings, right size, and yes correct torque, i disconected the oil gauge to bleed it and i have absolutly no oil pressure what so ever, didnt even move the air bubbles in the line

 

[Cheepjeep85]

you can try a new oil pump, but I gotta feeling its something more. Generally new oil pumps just don't give up. you get oil pressure from two places the oil pump and bearings, if either one is bad you get none. If you didn't replace the cam bearings on the first rebuild, they have 23 years on em wether they look like it or not they really should have been replaced, they are just as crucial as any other bearing.

Drooooid...2

 

[Old Dog]

Did you have oil pres. after the first rebuild?

 

[fzsk4p]

I just rebuilt a 88 I6 AMC 258 i6 / 4.2l its 6thous over and crank is 2 thou under, just put new rings in yesterday (did 2 rebuilds 1 with wrong rings), i replaced the sending unit with a mechanical one and put in a new oil pump between rebuilds, now it starts up with 20 to 40lbs and when its hot i have between 5-0 gauge doesnt read it, screen is clean ran a old oil filter after rebuild and replaced it after 30mins of running

so what should i do? could the oil pump go bad that fast? or am i missing somethin?

it was about 100 miles between rebuilds also its a 5spd jeep

Let`s narrow this down. The key is that it starts and has 20-40 lbs. Then it gets warm and goes to 0-5.

So what would cause a bleed off of pressure due to the oil thinning as it gets warm ? ............

Excessive clearances in bearings would make sense.

You say you installed new rod bearings. Did I miss anything comments on the mains ?

As Cheepjeep85 mentioned the cam bearings would be a suspect. Why did you think they did not need to be replaced ?

Strongly suspect there is a clearance issue with one of the three sets of bearings. Main, rod and cam.

 

[wrangler rider]

The motor was built before I got it, and bearings were tight but even if it was bearings I would still have some presuure enough to clear the gaugesline, but I don't have anything

 

[Cheepjeep85]

Were talking clearnces in the thousands of an inch, just because they feel tight doent mean they have proper clearance.

Drooooid...2

 

[wrangler rider]

Were talking clearnces in the thousands of an inch, just because they feel tight doent mean they have proper clearance.

Drooooid...2

oh well that doesnt help lol im not a computer i cant find that

 

[Cheepjeep85]

What it boils down to is this, you can try putting an oil pump in it, if you want, its the cheapest easiest thing you can do. its most likely not your problem, but bearings. if the cam bearings have never been replaced then almost a full rebuild will be needed. That means pulling it out (well I suppose you good leave it in but it'll be a pia), having the crank checked, having new cam bearings installed, and new rod and main bearings. Since it has been bored recently id probably go with another new set of rings, depending on how new they are and if you can remove the pistons without breaking them, you can probably reuse the timing set (assuming its recently new), you might be able to reuse the cam and lifters (again asuming they are recently new, and a machine shop checks out the cam), and you should be able to reuse everything else, but gaskets of course.

You should do some research on egine building, so you will now how to assemble everything, and measure for proper clearances (ie using plastigauge). I'm sure there are some good books out there on the subject. The haynes manual has some good info in there, and there are plenty of internet resources.

Drooooid...2

 

[wrangler rider]

ok so i put 20 50 oil in it and ran here till no pressure, pulled the pan and pump checked the pump no problems, pulled off a main bearing cap, and totally shot, they were great when i did the rebuild, also has new rings with 60miles on em, pifter, timing set, ect
so now i can pull the crank machine it and reinstall it for like 200$ and i dont know what the cam looks like

so now i can either scrap the motor and start all over, try to fix it and still possible not have oil pressure and waste about $400, or sell it all out right and start over with a new truck, what do yall think i should do?

 

[fzsk4p]

ok so i put 20 50 oil in it and ran here till no pressure, pulled the pan and pump checked the pump no problems, pulled off a main bearing cap, and totally shot, they were great when i did the rebuild, also has new rings with 60miles on em, pifter, timing set, ect
so now i can pull the crank machine it and reinstall it for like 200$ and i dont know what the cam looks like

so now i can either scrap the motor and start all over, try to fix it and still possible not have oil pressure and waste about $400, or sell it all out right and start over with a new truck, what do yall think i should do?

Take it down, rebuild it with good parts and run it for another 200,000 miles.

 

[Cheepjeep85]

Take it down, rebuild it with good parts and run it for another 200,000 miles.

Exactly, rebuild it right and you'll be happy with it garaunteed.


Drooooid...2

 

[wrangler rider]

Ight ill let you know whzt I decide on, I got the money but id rather spend it on my charger

 

[Cheepjeep85]

Ah the cj is more important

Drooooid...2

 

[Tommy]

Might be off the wall here but there may be a floaty where your gauge line attaches to the motor. It may get sucked into the line after it starts which would cause the gauge to read 0. Just a thought. I usually look for the simple things first. You didn't say if the motor was running good and reading no pressure. Is there oil moving in the top end while it's running? I think I would do more digging before I started tearing it down. Just a thought.

Tommy

 

[fzsk4p]

ok so i put 20 50 oil in it and ran here till no pressure, pulled the pan and pump checked the pump no problems, pulled off a main bearing cap, and totally shot, they were great when i did the rebuild, also has new rings with 60miles on em, pifter, timing set, ect
so now i can pull the crank machine it and reinstall it for like 200$ and i dont know what the cam looks like

so now i can either scrap the motor and start all over, try to fix it and still possible not have oil pressure and waste about $400, or sell it all out right and start over with a new truck, what do yall think i should do?

Might be off the wall here but there may be a floaty where your gauge line attaches to the motor. It may get sucked into the line after it starts which would cause the gauge to read 0. Just a thought. I usually look for the simple things first. You didn't say if the motor was running good and reading no pressure. Is there oil moving in the top end while it's running? I think I would do more digging before I started tearing it down. Just a thought.

Tommy

Anit no oil gonna be heading up top with mains that are shot. Abnd with worn mains the problem is only gonna get worese.

 

[Tommy]

My bad. I didn't see the post where he found the problem. Only got to the bottom of the first page when I replied. Didn't see it going to page two.

Tommy

 

[fzsk4p]

My bad. I didn't see the post where he found the problem. Only got to the bottom of the first page when I replied. Didn't see it going to page two.

Tommy

No worries Tommy.

Suspect the OP got (was given) mismatched parts and is now having to do the job over again.

 

[Cheepjeep85]

That's my guess to^^^^. You have a cranked turned you gotta make sure the bearings are exactly right, and needs to be verified with plastigauge.

Drooooid...2