4.0 engine knock

Airjunky

TJ Enthusiast
Joined
Dec 13, 2018
Messages
940
Location
Liberty Lake WA
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.
 
Put the engine at TDC on each cylinder and check for a loose rocker arm. Report back with your findings.
 
Messin around with a camera. Trying to figure out how to tell if I'm at TDC or 180 off

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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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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
 
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.
 
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.
 
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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