Help Diagnosing Engine Knock

JKP

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I think they should all be at the same height. If that is the only one at that height, I would guess burned valve or seat which means the head will have to be pulled.
 

SkylinesSuck

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So… I’m going to follow thru with the service bulletin, but does this indicate a bad valve seat? Why would the spring present itself higher? If I understand it’s sitting higher that means the valve is not stuck open but closed father than it should be?

I’m sure the answer would present itself with pulling the head but that’s a farther job than I might be willing to get into at this point.
Something similar to this could be holding the one valve open (down) a bit.

593687b4_df82_4019_adca_15234072c689_90ef5d9b8c359b114eb2a47aed19b45434aa07dc.jpeg
 

oconnef

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Something similar to this could be holding the one valve open (down) a bit.

View attachment 332034
That makes sense. Could the same be true if the valve is too far up? Once the rocker arms were off. You can see the exhaust valve was farther UP than down. If the “seat” is busted or burned, could that happen?

I guess I’m not 100% opposed to pulling the head, I just don’t know if there’s more trouble lurking on the bottom end as well.
 

pagrey

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One is high or one is low. I think installed height is around 1.6" Valves bend or stretch, seats get damaged and chunks of pistons or rings embed themselves in crazy places. I think you're going to find some interesting stuff when you pull the head. If you have a bore scope or are able to see there is a tiny possibility something crazy is wedged in there and when you pull the intake you'll be able to get at it but that's a Hail Mary for sure.

Edit: I have a feeling a bore scope in the spark plug hole would see some damage on the piston unfortunately you probably wont be able to look at the valve/seat.
 
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SkylinesSuck

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After breaking many things, one thing I can say is that things can break weird. No telling until you get a good look at what's going on. Any way you slice it that head is coming off I think.
 
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oconnef

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A little recap/catch up…

Ended up pulling the head and found a bad exhaust valve as expected. They also found a crack in the head. Boo. (Shout out to Cylinder Head Exchange in Sun Valley, CA).

I ended up getting a rebuilt head and installing with little issue, but now I’m getting the P0421 - which is basically a catalyst failure. Had a suspicion this would happen with misfire running for so long. Luckily there’s a Jeep junkyard nearby as well so I’m pulling the cats off of a junker and should be able to finally get back to CEL zero!

Ended up changing the lifters and everything in the top end. Hope to do the chain, cam and low end components eventually. Probably should’ve done it at the same time, but I was on a race to drivability.

There’s still some knock which I’m 99% certain is chain slap now. Cylinder bores looked fantastic and no evidence of blown piston rings or anything.

* added some before and after of the piston cleaning.

44F6D252-1A94-4D4D-9B7D-48D28EC3F6DE.jpeg


E4688D9E-9968-4B2E-AE02-FA62359D46ED.jpeg


7D4F4C1B-A427-46BE-A3E8-08D52B03627A.jpeg
 

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BJeepTJ

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That's me! Glad you found the thread! Thanks for sharing your experience as well!

Wow, just made it through this thread. Lots of good info here. I have the exact sound on my jeep 98 Manual 4.0 with 135K Miles, it started after and oil change and can't seem to get rid of it. Did you ever find the source?
 

fourpointzero

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Wow, just made it through this thread. Lots of good info here. I have the exact sound on my jeep 98 Manual 4.0 with 135K Miles, it started after and oil change and can't seem to get rid of it. Did you ever find the source?

Just keep driving and worry not. I have a similar "knock" and after a thorough warmup, it's gone. Restart after sitting a fee minutes and its there again, till its not.

Im almost at 200k and have a low end kock since the Jeep was at 129k. Some of them are noisy. I've yet to hear of one detonating because of said noise. If anyone can contest that, please have at it. ✌️
 
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The Goblin

The Goblin

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Wow, just made it through this thread. Lots of good info here. I have the exact sound on my jeep 98 Manual 4.0 with 135K Miles, it started after and oil change and can't seem to get rid of it. Did you ever find the source?

Welcome to the “got-a-random-knocking-sound-in-my-Jeep-and-I-can’t-figure-it-out” family. ;)

Lots of great info here. Hopefully you can figure yours out. If not, I agree with fourpointzero, worry not and carry on!

If you do figure something out, please share here so we can all learn.

Thanks!
 
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CODE5

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I'm hoping on board as well... UGH.

I had a blown head gasket and a cracked cylinder head. Repaired it all myself and installed the new cylinder head. I now have a sound I didn't have before... The engine (4.0L) now has a horrible knock/tick that will not go away. It does it cold/hot and seems to increase with the rpms of the engine. When I looked down into the valve cover I swear it looks like its not getting much oil to the top end of my engine. Would lots of sludge clog up an oil pump and cause this tick? I added MMO to the oil and it might have quieted some other noises but this still seems unaffected...

Here is a video I got of it.

 

bromel

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I'm hoping on board as well... UGH.

I had a blown head gasket and a cracked cylinder head. Repaired it all myself and installed the new cylinder head. I now have a sound I didn't have before... The engine (4.0L) now has a horrible knock/tick that will not go away. It does it cold/hot and seems to increase with the rpms of the engine. When I looked down into the valve cover I swear it looks like its not getting much oil to the top end of my engine. Would lots of sludge clog up an oil pump and cause this tick? I added MMO to the oil and it might have quieted some other noises but this still seems unaffected...

Here is a video I got of it.


Are you sure that's not an exhaust leak? Could be that or a stuck lifter, but that is not the noise in question from this thread.
 
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oconnef

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To me, the exhaust leaks sounds more like air puffing against your teeth or something. Easy enough to diagnose anyhow with smoke test or using carb cleaner or whatever the gurus here suggest around the exhaust/intake manifold gasket and where the carbs meet that manifold.
Lifter tick, IMO, sounds more like a mechanical tick. You *could* run the engine with the valve cover off and visually inspect to see if the oil is moving up the push rods, but that can be (really) messy. (I fashioned an aluminum foil "bowl" around the head when I did this to minimize splashing)

That noise (almost like a diesel) is almost dead on what I hear on mine. I believe it to be a fair, but not deadly, amount of piston slap. I recently did a top end rebuild and the only thing I noticed is that the piston chambers seemed to be smooth rather than cross-hatched - which could result in poor lubrication/oil movement: https://dannysengineportal.com/cylinder-bore-deglazing-purpose-crosshatch-roughness-and-angle/

It's worth noting I'm north of 280K miles as well, so it's certainly understandable if the piston rings have worn or the tolerance slop is there.

I plan on doing the lower end later to fix the leak in the rear main seal and oil pan gasket - but those are negligible too - not severe enough be leak more than a few drops between changes. At that time, I also wouldn't be shocked if the pistons need replacing and I'll consider, but still, she runs! So it's hard to justify and "unneeded" repair job based solely on sound. I'll try to record the sound for comparison.
 

CODE5

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Are you sure that's not an exhaust leak? Could be that or a stuck lifter, but that is not the noise in question from this thread.

I’m going to try the shop vac in the tail pipe and soapy water on the exhaust manifold to find some bubbles… I took it for it’s first test drive and after I got it warmed up oil pressure goes down from 40 to 20 to 0 at idle. So I guess I’ve got bigger problems 🤦🏻‍
 

SkylinesSuck

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Just get some help, wait until it's cold, then start it up and have someone hold an old towel balled up in the exhaust tip while you move your hand around near the exhaust manifold and feel for warm air blowing on it. It'll be obvious although it might be leaking in a direction that's hard to get to.
 

oconnef

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If* you're oil pump (OPDA) is going out, it's not a hard fix at all, just make sure to check some youtube videos on tips, as well as this forum. It's cheap (<200), but just pay attention to the calibration of it.

It could also be the source of some noise.
 

HusaBinPhartin

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Bought one with this piston slap noise. How many miles have you guys put on your jeep since the noise started? Also how long you think the motor will last?