Help diagnosing engine knock

IrishWake

TJ Enthusiast
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A couple of weeks ago, I started noticing a ticking/knocking noise while driving home from a trip that became apparent around 1700 RPM, peaked at 2000 RPM, and was drowned out by engine/wind noise above that. Engine temperatures were perfect and oil pressure was within what I would call normal (at least normal for the past 15,000 miles I've driven it). I popped the hood when I got home and the noise scared me enough to not drive it, and oil level was low (checked before the trip and it was fine). I parked it, and life got in the way for the next few weeks.

I'm finally getting around to trying to diagnose it, and as you're probably aware, every youtube video for 4.0 engine knock either doesn't record the actual noise, or it has 15 different diagnoses from 15 different people who "drove their brother's jeep once." I've found similar-sounding videos where the culprit was everything from lifter/rocker noise, to CPS, to exhaust leak, to piston slap and broken skirts. I wanted to post here to see if anyone had an idea before I get the time to tear this down and look at everything.

What I notice:
  • When driving, I only hear it nearing 2000 RPM. Always under acceleration, never when I'm constant at 2000 or decelerating through it
  • Noise happens cold, hot, does not seem to change with temp
  • From under the hood, it sounds noiser on the driver side
  • Using a mechanics stethoscope, it sounds loudest on the valve cover in the back half of the engine, but to the ear, the bottom of the engine sounds louder. Oil pan picks up no noise with stethoscope
  • No metal flakes in oil or magnetic particles.

I was planning to take apart the top end and see if anything had excess play or was stuck/collapsed, but have not yet had the time. I live in an apartment and am not "supposed" to work on a vehicle, so anything bottom end I will need to take it to a friend or a shop. Is it worth taking the top apart when I get time, or should I be expecting bottom end and just drive it to a better working location while it's still in one piece? (trailer is an option, but I do have to get it out of a parking garage). Any thoughts or suggestions for further diagnosis are appreciated
 
Well. Just read your breakdown. And almost exactly like mine.
Long time, many opinions and diagnosis,
Sounds the same. I would have a mechanic drop that oil pan Pronto, look at crank rod bearings. Mine had 126k.
Ran great, didn't smoke, throw any codes, but that knock.
One piston cracked, all bearings burned.
Just finishing my break in on my newly rebuilt 4.0, 500 miles on it. $4500 later.

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Ask @SamwiseGamJeep about his-

Also sharp avatar guy.
I should've said "Only good news appreciated" :LOL: . And thank you, I wish she was running as good as she looked in that pic...

Well. Just read your breakdown. And almost exactly like mine.
Long time, many opinions and diagnosis,
Sounds the same. I would have a mechanic drop that oil pan Pronto, look at crank rod bearings. Mine had 126k.
Ran great, didn't smoke, throw any codes, but that knock.
One piston cracked, all bearings burned.
Just finishing my break in on my newly rebuilt 4.0, 500 miles on it. $4500 later.
Oh boy. I've been reading through your thread the past hour, looks like I'm in for a treat. Thanks for weighing in, I guess I got a bit luckier with 200k, although luck does not seem to be on any of our sides. In talking to some friends, I may be able to source a donor 4.0, although I don't know the history. I'll probably get it there this weekend or next to take er apart and see what we find, then assess rebuild/replace/reman options. Not sure what shop reputations are around here yet.
 
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I should've said "Only good news appreciated" :LOL: . And thank you, I wish she was running as good as she looked in that pic...


Oh boy. I've been reading through your thread the past hour, looks like I'm in for a treat. Thanks for weighing in, I guess I got a bit luckier with 200k, although luck does not seem to be on any of our sides. One of the friends who has offered to help potentially has a donor 4.0, although I don't know the history. I'll probably get it there this weekend or next to take er apart and see what we find, then assess rebuild/replace/reman options. Not sure what shop reputations are around here yet.
Good deal man. Hate to be the bearer of the bad stuff.
And glad you went through the thread, was going to suggest that. Lot's of info that's not in there, but you get the jist. The pistons, and balancing, are a must. He is running fantastic. Good luck to you, and hope you have a kind, patient, understanding wife like I do.
Although after a year restoring this jeep, then the motor? Tested her immensely!
That was about the end of her rope.
The good news is, I sold my four wheeler, a golf cart, and three kayaks to pay for the motor build!
 
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I should've said "Only good news appreciated" :LOL: . And thank you, I wish she was running as good as she looked in that pic...


Oh boy. I've been reading through your thread the past hour, looks like I'm in for a treat. Thanks for weighing in, I guess I got a bit luckier with 200k, although luck does not seem to be on any of our sides. In talking to some friends, I may be able to source a donor 4.0, although I don't know the history. I'll probably get it there this weekend or next to take er apart and see what we find, then assess rebuild/replace/reman options. Not sure what shop reputations are around here yet.
Not trying to be a buzzkill, and it is unusual when these don’t run way north of 250,000 miles. Hate to see premature failures.
 
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Good deal man. Hate to be the bearer of the bad stuff.
And glad you went through the thread, was going to suggest that. Lot's of info that's not in there, but you get the jist. The pistons, and balancing, are a must. He is running fantastic. Good luck to you, and hope you have a kind, patient, understanding wife like I do.
Although after a year restoring this jeep, then the motor? Tested her immensely!
That was about the end of her rope.
The good news is, I sold my four wheeler, a golf cart, and three kayaks to pay for the motor build!
Don't have the wife to worry about yet, although I also don't have golf carts and four wheelers to help finance this. So... tradeoffs, I guess?

Not trying to be a buzzkill, and it is unusual when these don’t run way north of 250,000 miles. Hate to see premature failures.
I was kinda surprised, too. I never knew the early life of this Jeep, so I always assumed some sort of premature failure would happen, but I was hoping to make it until I had a garage or at least a driveway again to call my own to work on it. A friend came today to pick it up, it's going to another friend's house for us to tear down this weekend. He mentioned he has a headless WJ block with moderate miles taking up space, depending on how it looks I might go that route + a clearwater head. Any non-obvious pitfalls of going this route? He is checking the serial tonight to confirm it actually is from the WJ. Scratch that, it's a ZJ block. Guess I'll confirm the problem and start looking at the expensive options
 
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