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4.0 engine knock


Airjunky

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Dec 13, 2018
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Driving home from work on Thursday and the engine started developing a knock. Initially it sounded like it was low on oil, idled fine but sounded like valves when the engine got over 2500 or 3000 RPMs. Oil pressure was good, around 40 psi. I pulled over & checked the oil, no leaks, and was full. In the next few miles, the noise changed to a loud ticking. This weekend I pulled the valve cover and found the rockers & push rods were good, overall looked really good. I drained the oil and opened up the filter..... nothing very clean, no chunks. I did a compression test and compression came in from 120 - 140 psi..... #3 & 4 being the lower psi. Listening to it, it seems like it's coming from the front of the engine, maybe a timing chain tensioner?
Been doing a bunch of reading and listening to videos. Whether it be a timing chain, wrist pin, broken piston skirt, or whatever, it sounds like it's new engine time.
Dammit.
 

Daryl

2004 Rubicon
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Put the engine at TDC on each cylinder and check for a loose rocker arm. Report back with your findings.
 
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Airjunky

Airjunky

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I’m thinking something wrong with the valvetrain. Bad cam, lifter or ? How many miles on the engine?
That's kind of what I was thinking when the first noise started. Then I think something broke loose.
116k miles on it.
 

Nimbley

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Roll the engine over a little and watch the lifters. Intake valve will close before TDC. Exhaust valve will open after TDC. Generally a lower end knock will be a lower frequency and a top end noise will be a higher frequency. Think bass versus treble. In the video it kinda sounds like a collapsed lifter.
 
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Medali

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Tunis, Tunisia
Sorry to tell you, but it's exactly the same sound I heard one day before my engine creaked and broke ... In the end it was a broken piston due to the connecting rod that no more turns around its axis ... It was probably due to a problem with engine oil ...

Envoyé de mon MHA-L29 en utilisant Tapatalk
 
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Airjunky

Airjunky

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Sorry to tell you, but it's exactly the same sound I heard one day before my engine creaked and broke ... In the end it was a broken piston due to the connecting rod that no more turns around its axis ... It was probably due to a problem with engine oil ...

Envoyé de mon MHA-L29 en utilisant Tapatalk
I parked the Jeep a week or so ago. Hoping to pull the exhaust and oil pan to see what happened. Bought an engine stand from a neighbor. Need to get off my ass and get to dismantling the damn thing.
 
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Airjunky

Airjunky

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Got on the Jeep this morning and drained the oil, removed the exhaust, oil pan, starter and battery. Nothing glaringly obviously wrong, other than the wood screw in the bottom hole of the scatter shield & the loose bolts on the exhaust manifold/header. Still no chunks in the oil pan. And couldn't find anything bent or broken.
 

astjp2

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With the pan off, look up at the cam lobes, roll the enigne over BY HAND with a ratchet and socket on the crank pulley large bolt, if you have a wiped lobe, you will see it because it will be round instead of egg shaped. if not you can check the lifters, they do collapse and not hold pressure causing a click. rock the crank back and forth and watch each rod, you may see excessive play in the rod to crank position.
 
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dbbd1

go away...
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With the pan off, would the piston skirts be able to be seen?
 
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Airjunky

Airjunky

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With the pan off, would the piston skirts be able to be seen?
Yea, depends on how low the piston is.
I'll pull the plugs & turn it over. Should be cool.
My buddy thinks it was an exhaust leak. Two of the 4 bolts were hand tight or less.
 
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