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Unread 08-30-2010, 11:39 AM   #1
migsk8
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can i replace the rods and bearing from the bottom ?

ok so today as i was leaving the back i was accelerating like a grandma like usual, the jeep started shaking for a split second from the motor, i saw ton of black smoke come out from the rear view mirror, so i shut it off and guided into a parking spot. i look under the jeep and oil is pouring everywhere. this is what i find.



so my question to you guys is, if i threw a rod, can i replace the bearing and broken rod from the bottom of the jeep without even taking out the motor ?


what would be the easiest way to go about this ? i dont know exactly what happened yet but that is my guess, it blew up about 30 minutes ago and im about to tow it home in a little bit.

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Unread 08-30-2010, 11:44 AM   #2
Tony89
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I'm going to guess if you threw a rod like that, the chances of the block and crank still being ok, are probably about as good as my chances of the cherokee taking flight on the way home today.

To answer your question, no. The motor will have to be pulled and disassembled to check the block, crank, and possibly head.
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Unread 08-30-2010, 11:46 AM   #3
robsjeepxj
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You can do all the work with the motor in the jeep if that's how you want to do it , it will be a lot harder to work on that way though, but I don't think you can get the pistons and rods out from the bottom you'll need to pull the head. You can replace the bearings on the big end of the rods and the crank bearings from the bottom but that probably won't help you much I don't think.
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Unread 08-30-2010, 11:48 AM   #4
Saudade
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The easiest way would be to find a JY motor of a compatible year and swap it out.

While "technically" you could change the rod out, you have to drop the tranny so you can lower the crack to remove the piston (assuming it's not laying in the pan). IMO, it would entain so much work that pulling the motor would be easier.
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Unread 08-30-2010, 11:52 AM   #5
robsjeepxj
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I remember having to hone down the ridge on the top of the cylinder to get the pistons out the top, I would think it would be impossible to get it out from the bottom. Have you done this? And gotten the new piston in with all the new rings intact?
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Unread 08-30-2010, 12:54 PM   #6
fishermanfloyd
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That engine is junk without machine work.
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Unread 08-30-2010, 01:09 PM   #7
AZ Jeff
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1. you MAY be able to REMOVE the piston from the bottom, but you sure WILL NOT get it back IN from the bottom
2. the crankshaft is almost certainly screwed up on journal for the broken rod. You will not be able to sucessfully replace that bearing and have it last without having the journal ground for trueness.

For the above reasons, your engine cannot be repaired without the services of a machine shop and pulling the head.

One question for you, out of curiousity------

Aside from the shaking you reported, wasn't the engine making a ton of BAD NOISES before it failed? Rods RARELY break without giving warning sounds unless you are revving the engine to or past redline when they let loose.
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Unread 08-30-2010, 01:22 PM   #8
lowicz96
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Take the oil pan and head off to see the damage. A buddy and i replaced a broken rod in a hydrolocked heap and hes been driving for awhile. We just took a piston and rod from a spare motor and put it in a stock height YJ, it smoke a little but is probably the valve stem seals. The jeep didnt come with the oil pan but i think it was trashed too. Just be careful with the bearing sizes, piston size/rings and use assembly lube.

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Unread 08-30-2010, 02:27 PM   #9
rmack
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no, the engine needs to be pulled, inspected and cleaned to get the schrapnal out before you ever replace anything.
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Unread 08-30-2010, 03:15 PM   #10
migsk8
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Quote:
Originally Posted by AZ Jeff View Post
1. you MAY be able to REMOVE the piston from the bottom, but you sure WILL NOT get it back IN from the bottom
2. the crankshaft is almost certainly screwed up on journal for the broken rod. You will not be able to sucessfully replace that bearing and have it last without having the journal ground for trueness.

For the above reasons, your engine cannot be repaired without the services of a machine shop and pulling the head.

One question for you, out of curiousity------

Aside from the shaking you reported, wasn't the engine making a ton of BAD NOISES before it failed? Rods RARELY break without giving warning sounds unless you are revving the engine to or past redline when they let loose.
there was no noise pointing out rod knock, i was at about 1,800 rpms when it went. it was just a sudden split second shake then a boom. thats it.
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Unread 08-30-2010, 03:17 PM   #11
migsk8
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well crap, so pretty much buy a used motor and put it in.FML im so broke right now, anybody know where i can get a pretty good price on a used 4.0 for my 99 ?
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Unread 08-30-2010, 04:55 PM   #12
menace2
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Quote:
Originally Posted by migsk8 View Post
there was no noise pointing out rod knock, i was at about 1,800 rpms when it went. it was just a sudden split second shake then a boom. thats it.
Sometimes a cap or cap screw will just let go like that. I had a 4-banger do it, no warning.
The head does have to come off to replace the rod/piston. It can be done with the block in the Jeep though.
Just get a used motor. They are cheap and everywhere. The junkyards are full of 4.0 Jeeps these days. Insurance companies total older ones when body work is close to bluebook.
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Unread 08-30-2010, 05:00 PM   #13
migsk8
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will any 4.0 fit in it with all the accessories ? i still wanna keep my cruise control and all that =)
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Unread 08-30-2010, 05:09 PM   #14
menace2
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Almost. There are a couple of threads going on this, one guy just finished.
You don't say anywhere what year you have.
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Unread 08-30-2010, 05:50 PM   #15
migsk8
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its a 99, what motors are compatible with my accesories ? im guessing like 97-00. i dont want a 01 for obvious reasons i dont want to happen again
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