sambroom

TO ANYONE WHO JUST FOUND THIS THREAD FOR THE FIRST TIME: The issue was confirmed to be a bad thrust bearing and thrust face on the crank. Bugout4x4 and dave1123 were extremely helpful getting me through swapping the crank and main/rod bearings to resolve the issue, and subsequent issues, including a gov pressure solenoid code, which turned out was caused by a squashed wire. I learned a lot in this process and did my best to record it. I hope this experience can help others as well.


2004 Jeep Grand Cherokee 4.0 Automatic.

This is frustrating. I just finished installing a new-to-me engine with 60k miles. It started right up after I finished, I let it heat up as I added coolant to make sure the thermostat opened up, and everything seemed to be going great. It got up to operating temp and still running smooth as silk, so I hopped in to take it for a drive... When I went to put it into reverse, it made a terrible sound. It sounded like an air hammer on a frying pan. It went away the instant I put it back in park. I quickly found that the sound was the flex plate/torque converter bolts were hitting the mud guard while in gear. So here are the exact symptoms:

It happens in drive, neutral, and reverse, but not park.

It doesn't happen the instant I put it in gear every time, but eventually it will happen.

If I do drive it, the sound intensifies as load increases.

So far I have pulled off the inspection part of the mud guard and attempted to bend the accessible parts of the mudguard forward and more out of the way.... No change. In park, there appears to be at least 1/4 of an inch of clearance between the flex plate bolts and the mudguard at the bottom, so unless there is a section of mudflap that is closer near the top and out of sight, it seems my flex plate is somehow moving at least 1/4 of an inch forward when the engine is in gear.

I'm using my original flex plate. No cracks and perfectly flat by my measurement, though I can see about a 16th of an inch of vertical wobble as it runs.

The torque converter is properly installed. No question there. After the bell housing was bolted up, the torque converter spun freely until I bolted it to the flex plate.

So what am I looking at here? Thrust bearing? Or could it be something more simple?

Are there any tests I can do to narrow it down before I go pulling it apart again?

If it is a thrust bearing, can I replace it with the engine in the frame? Is there a way to get the oil pan off without removing the front axle? Please help.

sambroom

Just had a thought. My old motor was just worn out, not blown. I don't think it could have a bad thrust bearing because the crank shaft play is extremely small, and more to the point, it didn't let the flex plate get at the mudguard when it was in. I wonder if I ought to go ahead and drop the pan and attempt to remove the thrust bearing from the old engine for practice, and then install it in the new(er) engine if it is in good shape. Am I looking at a difficult job here? I can't find any writeups on doing this with the engine still in the frame, and I'm seriously not wanting to pull it again, or even drop the tranny if I can help it.

dave1123

Where's the shiny spots? Is it possible the starter mounting bolt is too long? I doubt the thrust bearing is the problem, but you can check it by prying on the crankshaft damper on the front. The torque converter is pressurized in any position except park so it could be moving forward slightly, but that should be only 1/32" at most or whatever the flexplate bends. Try a shorter starter bolt and see if that cures your problem. Maybe you used the wrong one.

sambroom

Good idea on checking the play from the front. I had it in my dumb brain that I would have to drop the tranny to check from the back. It is possible I used the wrong bolt. I had two of each... Maybe I used a transmission bell housing-block bolt. I'll pull the starter bolts and see if either of the tips are shiny. I looked for shiny spots as best I could in a short time yesterday. I think I saw one on the flexplate itself, outside of the tc bolts... I also thought I saw metal dust on the bolt heads, but that may have been me seeing what I expected to see in part. I'll take a real thorough look today.

I have the front end of the jeep on stands to give me room to work underneath. Would it be a bad idea to put the rear on stands also so I can get under it while its in gear to see what is happening? or maybe just put it in neutral?

sambroom

Oh whoops, the starter bolts wouldn't be shiny on the end if they were too long, they would be pushing the mudguard out though. I'll check them

sambroom

UPDATE. It's the thrust bearing. The crank moves forward at least 1/8 an inch.


I compared the movement to the old block sitting in the garage, and that one didn't move at all that I could detect.

So what am I looking at here? Am I going to have to pull this engine again? or is there a way to do the thrust bearing with the engine in the frame under the oil pan? I'm super frustrated because I paid top dollar for this engine since it was advertised as "like new" condition, and changing the engine out on this jeep was no picnic for me!

Bugout4x4

I have mine tore down in frame right now. But I had the head off already so this gave me room to jack the engine up just barely enough to get the pan off to change the bearings. I lifted the body as much as I could and unhooked the shocks to drop the axle down more, I don't know if there would have been enough room to get it off if the head had still been on it though? It was still a wrestle to get the pan out. Honestly, Of I ever do it again for any reason the engine is coming out where I can stand and work on it.

Something else... You might find the rods need to be changed also. Having it out will be much easier to work on if so.

sambroom

I guess another question is whether the thrust faces on my crank could be worn out as well... That would be really bad news.

Bugout4x4

The Bearings are designed to wear easier and faster than the crank, and putting in new bearings might help for several thousand miles more. But unfortunately this is one of those situations where you won't know anything at all for sure until you get inside and check it over good.

sambroom

Well getting the oil pan off wasn't as hard as I thought (good because I needed a little win), I just put the body on high stands, unbolted the shocks at the top, and pulled the starter. It came right down with a wiggle.


NOW. I have no idea what I'm doing when it comes to working on a bottom end. which one even is the thrust bearing? I read position 2, but is that from the front or back? it looks like I am going to need to remove the oil sump, anything I need to watch out for there? and there is that long bracket... Is there a crash course of "watch out for this" I need to know about? I'm reading the service manual now...

Bugout4x4

Great! it looks pretty clean too! I would take the time to check everyone of those bearings while it is off. Especially the bearings in the rods. I tore mine down and the rod cap bearings were like NEW and I said "cool", then I pushed the rod and piston up a little and checked the bearing in the rod and they were way way into the brass. Now I know for sure where my oil pressure was going after it warmed up. lol

Do you have a dial caliper to check your wear on the thrust faces?

dave1123

The thrust bearing clearance should be .0015" to .0065"! Notice the number of zeros! I've been thru all the specs I've got and didn't find any for the thrust bearing width, just check the endplay after installing a new one. If that's too much, replace the crankshaft! Everything is numbered from the front. I'm thinking you could put the new bearing on the crank journal and check the side clearance with feeler gauges.

That long bracket you speak of is a bearing cap stabilizer. This is not the first time I've heard of thrust bearing failure with the 4.0. I've never seen it on any but engines that run with manual transmissions and it's usually caused by holding down the clutch for long periods. I wonder if this engine is out of a Wrangler.

Bugout4x4

Yeah, I just went through this, I found out the same thing. I was fortunate though and was able to chase down all the exact measurement details from the new bearing manufacturer. Then I had to get out my calipers and a piece of paper and do some math to find my difference. lol

sambroom

It is out of a wrangler, but it was an automatic. I read the service manual, and now I have my old engine on the stand, upside down to practice. I'm to the point now where its time to remove the upper bearing. Im looking for a cotter pin haha. I already stuck in feeler gauges on the old block, after tapping the crank forward as far as it could go, and could stick in a .005 in gauge, but not a .006. So I guess its technically in spec, but only just. I read somewhere that it is a bad idea to used brand new bearings on an old crank... should I try to use the one from my old engine? or will I damage it getting it out?

sambroom

actually, I think what ill do is rent a dial caliper and see what kind of gap im looking at between the faces, then order a bearing to fit. Any suggestions where to get one?