4.0 Engine Rebuild?

KotaClewis

KotaClewis

New member
Hey Everyone!
So I have had my Jeep Grand Cherokee for over a year now and I've fallen completely in love with it. When I purchased the Jeep, it had 185k miles on it for $1000, it had a check engine light for the gas cap and a replaced transmission 30k ago. It ran great. I've put a little over 15k on it and it receaches 203k today. However last winter when it was cold and starting up for the first time every morning, I could hear a faint but noticeable knocking or ticking noise coming from mid to low engine. Also my oil pressure would sit around 60 and rise to 75 while driving cold.

The noise went away after a few minutes of driving and pressure would hang around 40-55, but it would happen every morning. It's gotten much worse this winter. The knocking is much more noticeable while driving while cold. Even when I let her warm up to operating temp she still knocks until I've driven a few miles.

I asked my dad and few people at my favorite AutoZone what they think it is and the consensus is that it's a worn bearing and that an oil blockage could be somewhere in the engine causing oil pressure rises. The people at AutoZone say it could be multiple bearings because of the noise pattern.

So I'm debating whether I could rebuild or replace or completely give up and get a new Jeep. I really love this Jeep and I really wanna keep it and build it but I'm not sure if a quality engine rebuild is a good option. I'm trying to work and go to school so having the Jeep be out of commision for a while could be an issue.

Any help would be appreciated so much.

Thanks! -Dakota

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High mileage 4.0s are prone to cracked piston skirts. (I’ve rebuilt a few myself for this reason). Also the oil pumps are known to go bad so if you rebuild I’d suggest replacing that as well.

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Pretty easy to check if this is your issue, drop your oil pan and you’ll find chunks of piston. While you’re there you can check the main rod bearings by grabbing and trying to wiggle the rods on the crank.

Pop the head off pop the bad piston out swap a new one onto the rod a few new gaskets rebuild good to go. Even the head bolts are reusable once. I did all 6 pistons, new valve stems, new lifters, oil pump, etc for under 300.




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Snboarder113 said:
High mileage 4.0s are prone to cracked piston skirts. (I’ve rebuilt a few myself for this reason). Also the oil pumps are known to go bad so if you rebuild I’d suggest replacing that as well.

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Pretty easy to check if this is your issue, drop your oil pan and you’ll find chunks of piston. While you’re there you can check the main rod bearings by grabbing and trying to wiggle the rods on the crank.

Pop the head off pop the bad piston out swap a new one onto the rod a few new gaskets rebuild good to go. Even the head bolts are reusable once. I did all 6 pistons, new valve stems, new lifters, oil pump, etc for under 300.




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Click to expand...
Would broken piston skirts result in a slight scraping noise? I've heard this a little too and I was figuring it was the oil struggling to get to the top of the engine while it was thick and preventing decent lubrication on start up. I'll definitely do this and inspect the main bearings while the pan is off and look for any metal. I'm hoping it's not bad and that a new oil pump might help oil flow to where it needs to go. I've heard they get clogged up with sludge over time.

Thank you for the advice, I really appreciate it. Fingers crossed that I can fix it!

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I developed a rod knock at 225K on my 4.0 when the engine got hot and thinned out the oil. Maybe a noisy lifter or a rod bearing. It's about $1400 to do a full rebuild if that's the route you go.
 
^^^This. My MJ, which I love, has 245,000 and it’s gonna need some love (lifters). $1,400 is a good number and it’s money well spent. Good luck!
 
BABOOZLE said:
I developed a rod knock at 225K on my 4.0 when the engine got hot and thinned out the oil. Maybe a noisy lifter or a rod bearing. It's about $1400 to do a full rebuild if that's the route you go.
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I could probably save up that amount in the next few months with tax returns coming up. I'll definitely consider a rebuild, I love this Jeep and I'll drive it until the wheels fall off.

Thanks!

Sent from my SM-G955U using WAYALIFE mobile app
 
Budget for:
  • Everything
  • The kitchen sink


Expect:
  • Cracked skirts
  • Bad oil pump
  • At least two collapsed lifters
  • Stretched timing chain
  • Worn cam lobe
  • Cracked valve seats
  • Head deck and refresh
  • New cam, valvetrain

As long as 4.0's last, I've yet to open a high-mileage one that didn't need a valvetrain and cam due to wear and oil starvation. If you're going to tear the thing apart, you might as well refresh everything you can possibly pull off the short block. Motor work is never cheap, but you get what you pay for. It's a good learning experience in patience and general maintenance knowledge, plus it's cool as hell to say you built that motor from the bare block.
 
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