Low oil pressure after "rebuild"

[tmurphss]

Buckle up this is going to be a long story.... Hopefully someone has some knowledge on this, thanks in advance for any information.

I bought a 2004 TJ 4.0 5 speed a few months ago, 174k documented miles (odometer didn't work when I got it, not sure how long it didn't work but it is fixed now)
Since I bought it I had to put new cats on it (front one was broken up and plugged like has happened to others) I pulled the oil pan off to just inspect everything and replaced the bearings anyway when I was in there. (SIDE NTOE the oem rod bearings had the oil hole, the replacements did not) It then eventually it developed a knocking type sound loud when cold then quieter, when warm- I thought it was a lifter, bearings looked ok. So i decided to tear it down for an in-frame rebuild. Everything was removed except cam/timing chain, and crank.

Results of disassembly inspection were 4/6 pistons had cracked skirts, though none were broken off, and one of the lifters on #5 cylinder was difficult to get out and had some fine particles that stuck to the magnet when I removed the lifter. I cleaned all that out with the magnet. Also, on the head, the intake valve on #6 cylinder was corroded and not seating. Was going to lap the valves but I couldn't get a clean seat, so I ended up taking the head with a new set of valves to a machine shop.

For the rebuild -
I honed/deglazed the cylinders and got new pistons and rings and put them in.
Rolled in new main bearings and installed new rod bearings (these had the oiling hole in them same as OEM).
New set of lifters/rockers/pushrods
Head job, pressure checked for crack, cut new valve seats, new valves and guides, decked surface. - basically a new head

Reassembled everything and it fired right up - held 2k rpm for 20 minutes for break-in since I had new lifters. I used lucas TB zinc-plus break-in additive.

I went for a test drive and when I got to a stop sign, clutch in and engine came to idle, oil pressure went to zero and check gauges light came on, (I know its a dummy light for basically you have pressure or you don't, I believe i have read the cutoff is 6 psi?)

Got back home and went to pull the oil cap off the vale cover to make sure I could see the oil getting up to the rockers and when I went to remove the cap I could barely get it off there was so much vacuum. Once I got the cap off though, and the vacuum was equalized the pressure gauge showed ok oil pressure again and the warning went away. It turns out some time before I got it, that the front pcv fitting in the valve cover that is supposed to be open was replaced with a rear one that has the restriction orifice in it. I think this was never a problem before because the engine had enough blow-by that it got enough air to equalize, but with the new rings and good seal it was pulling a vacuum. I replaced with the correct fitting and thought it was fixed.

The next day I started it up and oil pressure read zero, again oil was getting to the rockers, so figured its the sending unit, (it had also showed zero one day when leaving work but shut it down and restarted it and it was good again, didn't think anything of it until now) replaced the sending unit and sure enough showed oil pressure again (cold), so I went for a drive again. Once it got to operating temp it again showed low pressure.

Neither the oil or coolant look milky indicating a leak on either side.

So now my next step is going to be to hook up a mechanical gauge to see what my true oil pressure is and go from there. Probably will pull the pan again to check bearings too. In the mean time I am all ears on what anyone thinks could be the problem? Could the excessive vacuum have pulled oil out of the journals during break-in and worn the bearings and now I have excessive clearance contributing to the low pressure? The original rod bearings that I took out when I replaced them had the holes in the end that allow the oil to pass through the connecting rod to oil the cam I think, the first time I replaced the bearings they didn't have these holes, read alot on that and concluded that bearing manufacturers decided they didn't need them... anyway the replacement connecting rod bearings that I put back in with this rebuild have the hole again, could that be just enough to make my oil pressure too low when warmed up?

Again sorry for such a long post and I know there are thousands of low oil pressure posts and hate to add another one but I have a sort of unique situation with the vacuum and not sure if that could be contributing to any of my problems. Thanks everyone.

 

[ColoJeep]

Welcome to the Forum.
Did you "mike " (measure) each crank journal for the rods and the main bearings?
What size bearings did you purchase?
Also did you Plasticgage the mains and rods to check for in spec clearances ?
Have you rebuilt an engine before?
I am trying to gather a little information to assist you and the problem.
Hopefully I am not coming across like a Dick but this dosen't seem to add up.

I don't think " vacuum " is a contributing issue but you could leave the oil cap off and run
the engine and check pressures. Vacuum couldn't build in the engine with the cap removed.

 

[tmurphss]

I guess my reply didn’t go through, you’re not coming off as a dick at all I appreciate your response.

So far I have fixed the vacuum issue and installed the correct pcv fitting at the front of the valve cover. Cap is easily removed now.

This is my first time digging into an engine this deep. It was originally just going to be replacing lifters until I found the piston damage and head damage.

Prior to the rebuild there was not an oil pressure issue that I know of but I guess it could have been as low as 6 psi and still shown fine…

Since there was no issue prior to the rebuild with standard bearings I went back with standard bearings but these rod bearings do have the oiling hole where the first replacement set didn’t…

For this same reason I didn’t do any plastigauge or mic the journals, wouldnt have been able to on the mains anyway since it was still in the block, I just rolled the bearings in one at a time.

My next move is going to try to make sure the hole that the oil pressure sensor/switch threads in is clean and install a mechanical gauge to see what my true pressure is…

Again thanks for the response.

 

[ColoJeep]

Okay, now we have some basis to move ahead!
I appreciate your willingness to address your issues! Everyone starts somewhere, unfortunately you are starting
at a place FAR beyond your experience level.
For decades car manufactures have built engines with varying sizes of main and rod bearing sizes to reduce waste and downtime on the assemblely line.
Engines can have standard bearings, all undersize bearings, or a mix of everything.
Example, you could have a 4.0 that has 6 standard main bearings and 1 .020 undersize bearing, while having 4 .010 undersize rod bearings an 2 .020 undersize bearings.
Rebuilders measure and then grind all the journals to a uniform undersize size, ( eg. all .020 or .030 undersze )
With all these variables, you MUST measure and fit bearings accordingly or get a uniformly ground crank and matching bearings.
Hopefully nothings is damaged in your engine and you can get everything correct.
I suggest you READ , READ , Read, everything you can on engine rebuilding before you proceed.
Piston ring endgaps are another thing rookies overlook.
I wish you well and look forward to see how you address your engine!
Again Welcome to the Forum and Jeep Madness !!

 

[tmurphss]

Thanks for your response, I didn’t go into it completely blind I did research and watched many videos on YouTube before hand. I have engine experience, just haven’t gone this deep before.

The bearings that came out were standard, stamped std on the opposite of the bearing surface so I went back with them. I didn’t think I would be able to plastigauge the mains with the engine still in place. Normally you do it upside down for easy access and also then gravity isn’t pulling the crank down, figured that wouldn’t give accurate readings trying to plastigauge from underneath?

Are you saying that there could be a mix of different bearings from the factory?

 

[ColoJeep]

Are you saying that there could be a mix of different bearings from the factory?

There can be a mix of bearing inserts on EACH Journal! There are color codes painted on the adjacent cheek toward the rear end of the crankshaft.
For example, on a main bearing 1-6 with a green mark would use a .001 undersize upper insert and a .002 undersize lower insert.
A red mark would use a .010 undersize upper insert and a .010 undersize lower insert.
An orange mark would use a .001 undersize upper insert and a standard size lower insert !

At the end of the day miking each journal to determine the proper inserts are critical.
I am glad to hear you have some experience!

 

[pagrey]

For this same reason I didn’t do any plastigauge or mic the journals, wouldnt have been able to on the mains anyway since it was still in the block, I just rolled the bearings in one at a time.

You can use plastigauge on the mains when they are in the block. I've never really heard of anyone putting new bearings in an engine and not checking the clearances. Youtube is not a good resource for rebuilding an engine in my opinion.

 

[Gollywomper]

When I tore down a samurai motor there was no 2 bearings the same size in the whole motor. They put them together with near perfection when new. I guess that is why we get 200k out of them and never will repeat that on a rebuild.

 

[Jezza]

When I tore down a samurai motor there was no 2 bearings the same size in the whole motor. They put them together with near perfection when new. I guess that is why we get 200k out of them and never will repeat that on a rebuild.

The bearings in Japanese engines are far more precise. My S2000 has 6 or 7 different sizes of standard bearings. Each size is only 0.0001" or so thicker than the last. The bearing colors used during assembly are stamped in the crank.

 

[tmurphss]

Thanks for the replies everyone, I knew going into it it would be half-assed rebuild not completely pulling the engine, but not having an oil pressure problem before hand and all the cap bearings being standard, I just went back with it and didn't think checking would be needed. lesson learned haha. I had no idea that there could be mixed bearings from factory.

My plan is to verify true oil pressure with a mechanical gauge and go from there. if it is in fact low, I'll probably pull the pan and start plastigauging the mains.

If it comes down to it and i need some .001 bearings, does anyone have a source for them? I can't find any anywhere other than OEM mopar ones for like 20-30 bucks each...

 

[Gollywomper]

You may have to buy individual bearing which will cost more. This why rebuilds are an All or NOTHING thing in my book. Bearing swaps are no longer an easy deal these days

 

[ColoJeep]

My plan is to verify true oil pressure with a mechanical gauge and go from there. if it is in fact low, I'll probably pull the pan and start plastigauging the mains.

At this point why not Plasticgauge mains and rods?
You still don't know where the oil pressure loss is from.
The engine had oil pressure before you effected it.

 

[tmurphss]

The mechanical gauge will verify that it is not a faulty sending unit, as I have read that sometimes aftermarket ones can be picky. I replaced mine because it showed zero even when revving and I knew there was oil because i could see it flowing on top of the rockers, so I replaced it with a parts store cheap one and it showed pressure again, so I know at least the original was bad. The odds are that the new one is working properly and I am right around 6 psi idle pressure since the gauge will bounce good/bad at hot idle, the mechanical gauge will verify that.

On the note of having pressure before, that is true, as far as I know.... The FSM spec calls for hot idle pressure of 13 psi, but if the dummy gauge doesn't show anything except above or below 6 psi, I could have had hot idle pressure at 8 psi or something before and not known it and gauge still show to be good, so I am going to hook a mechanical gauge up more just for my own curiosity on this as well.

if the mechanical gauge shows pressure to be ok, then I will try to replace the sending unit with a Mopar replacement, if it shows low I will begin the clearance checking.

 

[Paul Land]

Buckle up this is going to be a long story.... Hopefully someone has some knowledge on this, thanks in advance for any information.

I bought a 2004 TJ 4.0 5 speed a few months ago, 174k documented miles (odometer didn't work when I got it, not sure how long it didn't work but it is fixed now)
Since I bought it I had to put new cats on it (front one was broken up and plugged like has happened to others) I pulled the oil pan off to just inspect everything and replaced the bearings anyway when I was in there. (SIDE NTOE the oem rod bearings had the oil hole, the replacements did not) It then eventually it developed a knocking type sound loud when cold then quieter, when warm- I thought it was a lifter, bearings looked ok. So i decided to tear it down for an in-frame rebuild. Everything was removed except cam/timing chain, and crank.

Results of disassembly inspection were 4/6 pistons had cracked skirts, though none were broken off, and one of the lifters on #5 cylinder was difficult to get out and had some fine particles that stuck to the magnet when I removed the lifter. I cleaned all that out with the magnet. Also, on the head, the intake valve on #6 cylinder was corroded and not seating. Was going to lap the valves but I couldn't get a clean seat, so I ended up taking the head with a new set of valves to a machine shop.

For the rebuild -
I honed/deglazed the cylinders and got new pistons and rings and put them in.
Rolled in new main bearings and installed new rod bearings (these had the oiling hole in them same as OEM).
New set of lifters/rockers/pushrods
Head job, pressure checked for crack, cut new valve seats, new valves and guides, decked surface. - basically a new head

Reassembled everything and it fired right up - held 2k rpm for 20 minutes for break-in since I had new lifters. I used lucas TB zinc-plus break-in additive.

I went for a test drive and when I got to a stop sign, clutch in and engine came to idle, oil pressure went to zero and check gauges light came on, (I know its a dummy light for basically you have pressure or you don't, I believe i have read the cutoff is 6 psi?)

Got back home and went to pull the oil cap off the vale cover to make sure I could see the oil getting up to the rockers and when I went to remove the cap I could barely get it off there was so much vacuum. Once I got the cap off though, and the vacuum was equalized the pressure gauge showed ok oil pressure again and the warning went away. It turns out some time before I got it, that the front pcv fitting in the valve cover that is supposed to be open was replaced with a rear one that has the restriction orifice in it. I think this was never a problem before because the engine had enough blow-by that it got enough air to equalize, but with the new rings and good seal it was pulling a vacuum. I replaced with the correct fitting and thought it was fixed.

The next day I started it up and oil pressure read zero, again oil was getting to the rockers, so figured its the sending unit, (it had also showed zero one day when leaving work but shut it down and restarted it and it was good again, didn't think anything of it until now) replaced the sending unit and sure enough showed oil pressure again (cold), so I went for a drive again. Once it got to operating temp it again showed low pressure.

Neither the oil or coolant look milky indicating a leak on either side.

So now my next step is going to be to hook up a mechanical gauge to see what my true oil pressure is and go from there. Probably will pull the pan again to check bearings too. In the mean time I am all ears on what anyone thinks could be the problem? Could the excessive vacuum have pulled oil out of the journals during break-in and worn the bearings and now I have excessive clearance contributing to the low pressure? The original rod bearings that I took out when I replaced them had the holes in the end that allow the oil to pass through the connecting rod to oil the cam I think, the first time I replaced the bearings they didn't have these holes, read alot on that and concluded that bearing manufacturers decided they didn't need them... anyway the replacement connecting rod bearings that I put back in with this rebuild have the hole again, could that be just enough to make my oil pressure too low when warmed up?

Again sorry for such a long post and I know there are thousands of low oil pressure posts and hate to add another one but I have a sort of unique situation with the vacuum and not sure if that could be contributing to any of my problems. Thanks everyone.

I had low pressure after Chevy 350 rebuild, turned out leak at Main Bearing.

 

[Clarythedrill]

There is a Youtube channel called Jeep Solid, and he has a series on rebuilding a stock 4.0 and a stroker. The year model is not the same as yours, but the process is the same. It is a great resource to use if you are rebuilding an engine with not previous experience.

 

[tmurphss]

There is a Youtube channel called Jeep Solid, and he has a series on rebuilding a stock 4.0 and a stroker. The year model is not the same as yours, but the process is the same. It is a great resource to use if you are rebuilding an engine with not previous experience.

I actually watched his whole set of videos before I started, was very informative.

 

[tmurphss]

Follow up for everyone. I ended up pulling the jeep back into the shop and pulled the pan, rolled in mopar .001 oversized main bearings. And buttoned it up. Drove around and all was good until hot, not engine coolant temp hot but oil temp hot, like after driving 20-30 minutes. Then the oil pressure would flutter and zero out if it idled for a couple seconds. I drove to work a couple days and it would only drop out once I got to work and stopped and idled in the parking spot. I remembered reading about faulty sensors right out of the box, and I had replaced mine in the original troubleshooting with a parts store cheap one. So for grins I replaced back with the stock sensor. I have driven it a few more times since then and the gauge hasn’t dropped out yet. Plan to hook a gauge up to it this week one day after the drive home when it’s hot to see what it truly is at idle, but for now ignorance is bliss and gauge is good so I am too….