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Knocking Noise

T

thatxjguy

NAXJA Forum User
Location
Florida
This isn't my Jeep, but my noise is 100% identical to this one.

https://www.youtube.com/watch?v=nFLAEJZ1J4g

Last night, I removed the flex plate inspection cover to try and tighten the torque converter. That was obviously the easier thing to do, so that's why I tried it first. No luck, that knock is still there.

Has anyone else had this exact style noise and knows what it is?
 
I don't know what it is but my advice is to buy an automotive stethoscope & listen to the engine (with noise present) at about 25 different places. Top of pistons (each), mid block, oil pan, bell housing, etc. Might not tell you exactly what it is but it will narrow it down some.
 
So I used a hollow piece of stainless steel tube as a stethoscope. I put it all along the bottom of the oil pan where all 6 cylinders are. I heard nothing.

Then, I put it against the flex plate inspection cover. The knocking sound was as loud as could be.

Now... I already tightened my torque converter as tight as I could possibly get it.

What could possibly be making the sound?
 
Flex plate is probably cracked / broken. Pull the inspection plate off, turn the motor by hand and clean the flex plate well enough you'd be able to see any cracks.
 
yossarian19 said:
Flex plate is probably cracked / broken. Pull the inspection plate off, turn the motor by hand and clean the flex plate well enough you'd be able to see any cracks.
Click to expand...

It's fine, checked it out, pulled all the bolts to clean them and applied blue loctite. The noise is worse in the video than it actually is.
 
Just because mine sounds the same..
Is there a DIY or walk through that you guys know about for checking the flex plate bolts.

Dono too to much about my XJ yet.. Still trying to learn and read
But I would love to kill this sound
 
Yeah I'm looking into the flex plate as the issue.

Basically, yesterday I was able to narrow down with a stethoscope that the sound isn't coming from the bottom end of the motor.

It's coming from the transmission near the flex plate inspection cover. So it's one of two things – the flex plate or the torque converter, and I already tightened the torque converter. So I'm leaning towards flex plate.

In the mean time, just in case, I will be running Lucas oil additive to thicken the oil I use. That will basically answer my question right then and there about whether or not it's the motor. If it's a rod, the thicker oil additive will help quiet it down. If the noise persists, I know it's in the transmission.
 
i've seen 2 flex plates cracked in a circle around the crank flange, and the 2 peices held eachother like a puzzle. the surfaces just beat eachother up and that is the noise you hear. it made noise at idle, noise when on and off the throttle, and when shifting the trans and mostly went away for the most part under load.
i cant hear your video so i'm just telling wha t ive heard.
grab the flex plate and turn it back and forth with someone watching the engine front pulley. the more it wears the more it is noticeable with that method. or you may feel a slight "click" if you try to move it quickly.
how lose were the TC bolts? if they run lose they can elongate the flexplate holes which may continue to rattle even when they are tight but it would lessen the noise if that were the case so that would be an indicator as well.

also, your theory about the additive isnt totally correct. increasing your oil viscosity can quiet down a bearing noise, but if you have worn wrist pins or lower cylinder piston slap it wont do anything at all..
 
I ran some Lucas oil additive to thicken the oil a bit, and the knocking is still pretty noticeable. It didn't really change anything.

Does anyone have experience with this kind of noise and a possible problem and solution?
 
It's the flex plate, mine sounds the same. I decided to run it till something breaks. Mine is worse when everything is cold and practically goes a way when warm. It hasn't gotten worse in the past 1000 miles, so i'm not worried.
 
thatxjguy said:
Here's another video, this one is actually my Jeep and not someone else's.

The problem is still existent to this day:

https://www.youtube.com/watch?v=yFyxA9EMOqc

I'm still open to any suggestions. I have looked into the flex plate and I don't believe that's the case.
Click to expand...

When was your timing chain replaced? I am in the middle of tearing down my LJ's front end since that it what I suspect it is now.
 
disconnect injectors one at a time and see if the noise goes away. If it does, its likely the bottom end. If not, then well your list of 1000 possible causes is down to only about 900
 
thatxjguy said:
I've never replaced it before. I suspect it's never been replaced in the vehicle's entire service life.
Click to expand...

There was about 1" of deflection in my MJ's timing chain when I rebuilt the motor. 0.5" is the replacement point.

I just got the timing cover off my LJ. Over 0.5" of deflection in the chain, rub marks on the cover, and one of the mounting tabs for the chain guide broke off causing it to slap against the inside of the cover. I do not know if that will solve my knocking noise yet, but I have fixed four different noise sources over the past two days. :p
 
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