Im changing the connecting rod bearings in my 4.0 and I am having trouble getting the caps to go back on. They came off relatively easy when pulled straight down with a little force and grip, but only go back like half way. Theres not even enough thread to start the nuts. Do these need to be pressed on? I cant find any youtube videos that illustrate this step. Seems like everyone just slides them on. Im talking only about the rods not the mains. Engine is in the vehicle.

 

Well that is a bold venture, and I am interested to follow this and see how you do. Was the object to restore oil pressure?
Are you having the same difficulty with all 6 caps? You do have to put them on the same way they came off, I would hope you marked them with a punch or stamp 1-6 first?. Also they have to go on with the same side pointed to front.

Try rotating the crank up to get the best shot at them?

 

Engine had a pretty bad head gasket leak, for an unknown length of time when I bought it, and Im not ready to rebuild it just yet. Im hoping to use it as a daily for a couple months first. Finished the top half but it sounded like some rods were knocking and I needed to do the rear main seal anyway, so I went on an exploratory mission. Bearings were definitely worn so $30 to change them out seemed reasonable. Mine are marked with 1-6 stamps already and its pretty easy to tell which way is correct because of the lock tabs and oil hole being on opposite sides. I did try the other way around just to see but same thing.

 

Well it sounds odd but this is nothing I have done before to this engine anyway. Maybe a machine shop could guide you. Cant think of anything off my head at the moment. Are you sure you had a rod knock and not piston slap? If you did have a rod knock,..there might be alot more damaged than just the bearings.

 

Will they fit on without the new bearings? Suspect the new bearings.
If you have the infamous 0331 head are you sure the head wasn't cracked?

 

Honestly, Im not sure of anything lol. I figured since I was in there for the rms anyway, might as well take a look. Could be the torque converter, could be pistons. I do know that the bearings are worn down to the brass but not unevenly and the crank is smooth like butter so idk. Kinda assuming it wouldnt hurt to change em but not sure if it will solve any problems. I asked my mechanic and he thinks a stud is just a little crooked. Gunna try to put a little pressure on the studs and cross my toes. Hoping i dont do more damage than i had. Definitely planning to up my oil viscosity and use some lucas until i can rebuild this completely. Cylinders dont look too shabby.

 

If its a 2001 and some 2000s just about every 0331 head ends up cracking its a very very very well known defect. If your rods are bent too you're in deep do do there. If the heads off I would consider replacing the pistons, check the crank for out of round journal, bent rod, ..man ..you in deep there. maybe new block and head.

 

97grand4.0 you win! It was the new bearings!! Too thick. Goes on just fine with the old bearing. Damn, that was some grey hair i could have avoided if i had stopped to use my brain 😜...so im guessing undersized bearings is what I need, not standard?

 

Are we talking about a single cylinder here or are they all like this?

 

Looks like they are all. I was going one at a time but ive pulled three and all the same so far. The standard is .0057 and the under sized go from .003-.001. Hard to get a good measurement but the old ones were about .001 ish but those are pretty worn. I ordered a couple to compare but i guess i’ll find out for sure with some plastguage. My book is for older models but its pretty consistently .001-.002 of tolerance for the oil clearance. Wish i would have thought of this before but its ok, im learning.

 

If you're trying to fix the rms, fix the rms. Changing the rod bearings isn't going to fix a rod knock anyhow, if you have one, which you probably don't. And if you did, the thing to do would be plastigage them all to find one with way excessive clearance. And then take the crank out and check it, check rod, piston, etc etc.
I could be wrong, but dont bearings come in OE size, and oversize, not UNDER size, in increments of .010 not .001. So if you put oversize bearings in without plasti=gauging first to see what the actual clearances are, number one you don't even know if you NEED bearings at all, number 2, you would replace with the same size that was in there when it was built. So I guess Im not understanding at all when you say "The standard is .0057 and the under sized go from .003-.001"

 

BTW , 10 oversize bearings would require you to turn the crank 10 under.

 

Oh ya, .01-.03 whoops. But yes they do come undersized. What I cant seem to find is the numbers on the original ones. I just assumed that standard was the same but they are significantly thicker than the originals. At first I thought that was because they were new and not worn down but they do not allow the cap to go on even with force so I have to figure they are not correct. With the digital gauge the old ones read around .012 and the new standard ones came out to .057. My goal was to put the same size as what I had on there. When I first took them off, I was just looking for a smoking gun but since I had them off, I figured it wouldn't hurt to change them. I believe you are right that I never had a rod knock to begin with. Problem is that Im very inexperienced and not good at diagnosing so Im using process of elimination instead. My next best guess is my torque converter which actually makes more sense because it was having some issues shifting properly. I only paid $400 for this jeep and the education Im getting by digging in is helping me a lot, but theres a pretty good chance that it will still be loud and rough when Im done. Head was not cracked, I dont think. Pistons and cylinders “looked” decent. But I love your suggestion to use the plastiguage to determine if one is bad. I was going to do that after installing the new bearings anyway...I’ll go ahead and do that first.

 

99% of the time, the bearing will say what size they are on the backside of them. Can you post some pictures of the back of both the old and new bearings? Or do you know what part number your new bearings are?

 

I looked at rockauto, they do call them undersize, but that can only mean that they are oversize because the cranks are never going to be larger than they were from the factory. so that’s just the way they call them. As mentioned they most likely will say on the back what size they are. For that matter you can't assume that it was never rebuilt, either, and there could be different sizes for different years? I why you always, always check your final assy with plastigage.
If your head has the 0331 on the casting, you should just assume it is defective and replace it with one that is not the 0331. There are whole threads on this, and you can find where to find the numbers on the head.
Which is why you should test and not assume you had a bad head gasket, which I doubt.
I also doubt you had a rod knock, more likely piston slap, if it improved when warmed up.