new rod bearings for the 4.0

I have a 89 cherokee with 203,000 miles.. I bought it and it seems to have a quiet knock coming from the low end of the motor. I am thinking it is a loose rod bearing. I've driven the Jeep about 600 miles since I bought it and the knock hasn't changed. Also I only hear it when it is idling. I am thinking of replacing the bearings to eliminate that knock and make sure it dosent get worse ! I want this motor to last me another 100,000 miles

Anyone done this ? Good idea to do it ? What else should I do while I'm at it ?

Thanks !
Dan

dan89XJ said:

I have a 89 cherokee with 203,000 miles.. I bought it and it seems to have a quiet knock coming from the low end of the motor. I am thinking it is a loose rod bearing. I've driven the Jeep about 600 miles since I bought it and the knock hasn't changed. Also I only hear it when it is idling. I am thinking of replacing the bearings to eliminate that knock and make sure it dosent get worse ! I want this motor to last me another 100,000 miles

Anyone done this ? Good idea to do it ? What else should I do while I'm at it ?

Thanks !
Dan

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Sounds more like a wrist pin? I've seen them knock for long times and never get considerably worse. I have a 454 that has a hollow knock at idle and it is a sloppy wrist pin. It's been doin it for 40K and has never gotten louder. Make sure to know if it's knocking at crank or cam speed! If it was a rod it WILL get louder once it starts making noise! Rod knocks are almost always terminal. Good Luck!

FUNKYTEE5

If you hear it only at idle, it may not be a rod bearing. If you have an automatic transmission, drop the inspection cover (at the bottom of the bell housing) and check to be sure the bolts holding the torque converter to the flex plate (flywheel) are tight. If not, take them out, apply Loctite, reinstall and torque to spec. If the bolts appear tight, inspect the flex plate for an annular crack right around the outer perimeter of the reinforcing ring for the bolts holding the flex plate to the crankshaft.

Both of these problems causes a knocking sound that sounds like a rod, but is heard only at idle. Put the engine in gear and apply a slight amount of throttle against the brakes, and the load on the trasmission takes out any free play and the noise stops.

Somebody within the past couple of days just had the same problem, and his was loose (and missing) torque converter bolts. He even posted nice pics to guide you. Look for a thread with a title something like "OMG! What am I missing?"

dan89XJ said:

I have a 89 cherokee with 203,000 miles.. I bought it and it seems to have a quiet knock coming from the low end of the motor. I am thinking it is a loose rod bearing. I've driven the Jeep about 600 miles since I bought it and the knock hasn't changed. Also I only hear it when it is idling. I am thinking of replacing the bearings to eliminate that knock and make sure it dosent get worse ! I want this motor to last me another 100,000 miles

Anyone done this ? Good idea to do it ? What else should I do while I'm at it ?

Thanks !
Dan

Click to expand...

Loose rod bearing clearances are usually accompanied by low oil pressure especially when the engine's at idle. What oil pressure does your engine have when hot?

dan89XJ said:

I have a 89 cherokee with 203,000 miles.. I bought it and it seems to have a quiet knock coming from the low end of the motor. I am thinking it is a loose rod bearing. I've driven the Jeep about 600 miles since I bought it and the knock hasn't changed. Also I only hear it when it is idling. I am thinking of replacing the bearings to eliminate that knock and make sure it dosent get worse ! I want this motor to last me another 100,000 miles

Anyone done this ? Good idea to do it ? What else should I do while I'm at it ?

Thanks !
Dan

Click to expand...

Marginal rod bearing clearances will result in knocking noise that goes away under load and full de-acceleration (engine braking) conditions. It will sound-out mostly at "feather-speed" or coasting in gear on the road. I know, I've driven 2-3 engines with bad rod bearings. Once they get really bad, they will knock loudly at all speeds, low oil pressure, etc.

I wouldn't be surprised if there might be some piston slap going on here? It's easy to confuse and hard to identify any sound and especially knocking noises. Loose timing chain? Flex-plate, as mentioned.

Servicing 4.0 rod bearings in-frame wouldn't go very well. The actual bearing sizes are individually fitted from the factory so getting the proper working clearances under the vehicle is gonna be nearly impossible. I've never done that, but I wouldn't even try.

XJXJ said:

Servicing 4.0 rod bearings in-frame wouldn't go very well. The actual bearing sizes are individually fitted from the factory so getting the proper working clearances under the vehicle is gonna be nearly impossible. I've never done that, but I wouldn't even try.

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I would try it.

A lot of members have done rod bearings in-place. I know two North Atlantic Chapter members who did it. No problems, other than getting the oil pan off without bending the lip too severely.

I recently did a bearing job with a friend of mine to his '94 XJ with a 4.0. His oil pressure light was blinking at hot idle, around 180k miles on it. He was famous for the 15k mile oil change with whatever was cheapest. The engine made no audible knocking noises, but as it turns out the rod bearings were shot. The bearings must have to be really shot to make noise. If I were you I would measure the hot idle oil pressure with a mechanical gauge before assuming it's the rod bearings.

We did the rods, mains, high-volume oil pump, and rear main seal. The main bearings looked decent, but the rod bearings on the top side were all down to copper. We didn't worry about matching up all of the bearing sizes exactly, we just bought standard size bearings and put them in. The bearings in the engine were mixed about 50:50 standard size and 0.001" over. I figured that the replacement bearings were going to fit better than the bearings that were in it, and oversized bearings were going to be a crap-shoot without actually plastiguaging it. In hindsight next time I might just purchase all 0.001" over bearings. The high-volume oil pump didn't want to fit in the pan, so I had to modify the pan a little with a ball-pien hammer and grind a little off of the edge of the pump.

On a stock XJ the pan can be a real SOB to get out. We ended up jacking on the bellhousing to lift the motor away from the axle, with the axle hanging all the way down.

All is well now but boy was it a lot of work. My friend loves the clutch feel now that it doesn't have oil pouring on it from the rear main. The new-found oil pressure has shown the oil filter adapter o-rings to be in need of replacement.

I had 1 bolt 1/8 out on the flywheel and it was making a loud knock at idle only. make sure you check this first.....Jason

Thanks for the tips guys..

I did check the oil pressure with a manual gauge, I got 30psi at idle.. but the engien wasnt hot.

I'll check the flywheel..

I'll be sure to schedual a good amount of time to do this rod bearing job. It sounds like it'll be diffcult because of that pan.

Thanks again,
Dan

dan89XJ said:

Thanks for the tips guys..

I did check the oil pressure with a manual gauge, I got 30psi at idle.. but the engien wasnt hot.

I'll check the flywheel..

I'll be sure to schedual a good amount of time to do this rod bearing job. It sounds like it'll be diffcult because of that pan.

Thanks again,
Dan

Click to expand...

If it isn't the rod's or the flywheel I put money on a sloppy wristpin. Just a guess, but i've seen it before

FUNKYTEE5

dan89XJ said:

Thanks for the tips guys..

I did check the oil pressure with a manual gauge, I got 30psi at idle.. but the engien wasnt hot.

I'll check the flywheel..

I'll be sure to schedual a good amount of time to do this rod bearing job. It sounds like it'll be diffcult because of that pan.

Thanks again,
Dan

Click to expand...

If it isn't the rod's or the flywheel I'll put money on a sloppy wristpin. Just a guess, but i've seen it before

FUNKYTEE5

Try this first! I got a 96 last June and the first time I changed the oil it sounded like a diesel. After replacing the rod bearings, yes they were mixed also, and high volume oil pump that fit fine I still had the knock(s). What ended up quieting the engine down was Restore. It was like magic as I poured it into the running engine the knocks dissappeared. You need to use it at every oil change. I think my problem was piston slap.

JoBo