Need advice on rod/main bearing job

[Flash]

Quick update -

Replaced oil sender today. 60psi cold!! I drove for about 15miles and did some slow cruising on the beach in 4HI. Temps got up to high 220s (have an overheating issue I have to tackle ). Anyway, at that temp, I'm seeing 20 idle and 35-40 at 1500 RPM cruising. When it gets back to 210 on the highway, I'm seeing 30 / 45-50 respectavly.

I'm really hoping that this is an exhaust leak. I know it's hard to explain noises, but when I passed by a construction area that had diesel powered pumps running I thought to myself that is what my engine kinda sounds like. Chattery. I've had it "diesel" before when I sank it in a water/mud hole, so not like that - that was WAY loud, but afterwards my motor seemed quieter than before I entered the hole. I almost wondered if it was a manifold crack that was sealed w/ mud. Is that even possible? It is original, so it has 16yrs and 167k on it. It sounds like it's coming from the lower end though - not top of motor and it's louder on manifold side than passenger. Previous owner said it was rod bearings and that it'd been making that noise for a lil over 2yrs. I just figured it was and after the brakes went, he said screw it and sold it before it just blew up. Guess I need to order an APN header to find out for sure.

Them are good numbers!

could be a lifter going bad or stuck, but i haven't heard you talk a bought, lack of power so my best guess is a ext leak!

get a long rubber hose and stick one end in you ear(no not jocking:laugh3: ) and then move the other end of the hose around all the ext manifold........if its leaking there, you will find it when you brush upon the bad spot!

start with it above the eng, and see of its on the passenger side or driver side to begin with. then place the one end of the hose under the intake and see what you hear! Try it it works vary well!

Flash.

 

[88xjlover]

Them are good numbers!

could be a lifter going bad or stuck, but i haven't heard you talk a bought, lack of power so my best guess is a ext leak!

get a long rubber hose and stick one end in you ear(no not jocking:laugh3: ) and then move the other end of the hose around all the ext manifold........if its leaking there, you will find it when you brush upon the bad spot!

start with it above the eng, and see of its on the passenger side or driver side to begin with. then place the one end of the hose under the intake and see what you hear! Try it it works vary well!

Flash.

Flash is right those are great oil pressure #'s.
I can't imagine mud being strong enough to seal an exhaust leak.
Another idea is a timing issue can sound like "dieseling". My old 88 had such a problem and made lotsa noise and had an oil pressure that went down to about 5 when all warmed up but I still ran and wheeled the :firedevil out of it!
Never let me down. People thought I was crazy but I just told them the Jeep had a growl. :roll:

 

[gump]

I will now share my sob story with you. I have a 90 4.0 auto, it had real low oil pressure when I bought it, but only a light lifter tick, and at 155 k I figured it'll run forever like this. It has, but the oil pressure has gotten to the point where at hot idle it's about zero and it has developed a low knock at idle, goes away with rpm and the oil pressure goes up as well. Maybe 18-20 psi cruising down the highway. So, a few months ago I decided to go for a very budget minded freshening up. Left the engine in, pulled the pan, pulled the head, looked at the crank journals and they looked ok. Replaced the main and rod bearings, replaced the rings,didn't see any cracks or other visible problems in the pistons or rods and the wristpins felt tight. Also replaced the rear main and the oil pump. Got it back together, and once I got it started (long battle and still to this day don't know what the issue was) it had better oil pressure. Still not great, but better, and the knock disappeared. For approximately 2 hours of driving. Sure enough, the knock is back, and oil pressure? What oil pressure? I'm starting to question cam bearings. I don't know, and I now have a used engine sitting in the shop waiting to be installed. I have upwards of 300 bucks into parts for the refresh, and another 100 into the used powertrain (got the engine/trans/t-case as a unit). My wife has not let me forget. My point? If I had it to do over, I would either do a complete and proper re-build or stick a cheap used engine in there.

 

[gone postal]

Yeah, I've heard the if the bearings are worn, then the next ones will either wear rapidly to the old ones state or starve the crank / rod of oil and then BOOM. Funny how engines can be so different though b/c I've seen several people on here say that they just redo theirs once a year - one guy had been doing this for the last 3 or 4 years!! If its just bearings, it's not expensive, but is a PITA and time consuming.

I'm starting to question the "bad rod bearing" story i was told by previous owner though. Is it possible to have a bad bearing and have oil pressure like I do? I'm going to search around w/ a hose tonight and see if I can narrow it down. Someone else said that a failing water pump can make a similar noise. That's what I'm worried about...not being able to narrow it down - I don't want to though new part after new part at it...

 

[XJXJ]

Bearing job? 4.0 is one of the most tight tolerance engines I've ever seen regarding main/rod bearings. Ain't no way you'll help anything by changing bearings in frame and/or without a crank grind and precision bearing fit. Factory used different bearings on different journals to achieve exact tolerances. I think they're even color coded. And let's not forget align bore and/or deflection while we're in there?

Forget guesswork, forget what the seller told you - a loose rod might knock a little at idle, barely any knock as load is applied and the loudest knock when feathering the throttle while cruising. In other words it will change depending on the engine load & speed. I've had several engines (not 4.0's) to learn sound of bad rod bearings.

You probably have piston or timing chain slapping around but crankshaft is the least of my worry in regard to 4.0 problems.

Mine is 300k miles and still running very well - head or oilpan never off.

If radiator is 8-10 years old, due to lime scale buildup insulating things inside, it's not gonna cool anything like it should and overheating will always be a problem after replacing everything else (water pump, thermostat, fan clutch, etc.) Get a NEW radiator.

Until you get some experience never be too sure of anything!

 

[gone postal]

Bearing job? 4.0 is one of the most tight tolerance engines I've ever seen regarding main/rod bearings. Ain't no way you'll help anything by changing bearings in frame and/or without a crank grind and precision bearing fit. Factory used different bearings on different journals to achieve exact tolerances. I think they're even color coded. And let's not forget align bore and/or deflection while we're in there?

Forget guesswork, forget what the seller told you - a loose rod might knock a little at idle, barely any knock as load is applied and the loudest knock when feathering the throttle while cruising. In other words it will change depending on the engine load & speed. I've had several engines (not 4.0's) to learn sound of bad rod bearings.

You probably have piston or timing chain slapping around but crankshaft is the least of my worry in regard to 4.0 problems.

Mine is 300k miles and still running very well - head or oilpan never off.

If radiator is 8-10 years old, due to lime scale buildup insulating things inside, it's not gonna cool anything like it should and overheating will always be a problem after replacing everything else (water pump, thermostat, fan clutch, etc.) Get a NEW radiator.

Until you get some experience never be too sure of anything!

I appreciate your help. The knock is constant - idle, running, load, etc. It gets faster as the revs increase, so it's gotta be mechanically linked. It seems loudest when cold.

I'm in the process of moving right now, so I haven't had a chance to mess with it - lot going on w/ packing, closing on the house, etc. I'll be able to tear into it next weekend. I know it's been somewhat neglected, so I'm going to pull the radiator and replace that, mech. fan clutch, hoses and timing chain. I know that all of those minus chain need to be done and the chain can't hurt. Worse case scenario and this thing blows, it's not like those items will go to waste.

 

[nick86]

One last scenerio, and an easy check. If it is an auto, I have had loose torque converter bolt sound just like a bad rod. Even had machine guy listen to it and swear it was a rod. Found bolts loose while starting to pull motor. This has happened twice to me . Once w/ small block chevy, and once on my cj5.

 

[gone postal]

One last scenerio, and an easy check. If it is an auto, I have had loose torque converter bolt sound just like a bad rod. Even had machine guy listen to it and swear it was a rod. Found bolts loose while starting to pull motor. This has happened twice to me . Once w/ small block chevy, and once on my cj5.

already tightened them down. I retested for them too by holding the brake and pushing go pedal to load up the tranny. If they are loose, then it'll stop pinging when under load. I'm sure you already know that, but in case someone that doesn't stumbles across the thread...

 

[XJXJ]

I appreciate your help. The knock is constant - idle, running, load, etc. It gets faster as the revs increase, so it's gotta be mechanically linked. It seems loudest when cold.

Constant? Unless it's a really, really bad rod journal (oil pressure near zero) it's not that. Probably piston slap, common on many 4.0's and usually worse when cold, follows RPM. Timing chain is very high wear item in that engine and since it doesn't bang valves to pistons if it breaks it's not a high priority in many garage. Of course, if the chain's banging into the housing, you need to correct that and periodically renewing oil seals is always a good thing to do with that engine anyway.

Mechanic stethoscope or just hard/soft tubing held to your ear can help locate sources of mechanical noise more easily.

Careful compression test and ultimately a calibrated leakdown test is very reliable for qualifying engine condition without major teardown work. Depends on who's interpreting results but good data can reveal it all.

great, reliable vehicles when you get 'em running good.