piston replacement on Jeep 4.0

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I have a '98 Cherokee with 181k miles. I bought it last summer to use as a winter beater, but last fall, the #6 piston broke (found a couple pieces of the skirt in the oil pan). It sat all winter, as my garage is unheated. Now I need to decide what to do with it. My options seem to be: 1. pull the head and replace the piston, 2. do a full rebuild, or 3. find a good used engine.

I was originally going to rebuild, but honestly, I'm starting to lean toward option 1. I'm not normally one to take the cheap-n-dirty way out, but I'm considering it here because: the Jeep is in decent shape, but certainly not perfect; only using it in the winter, I won't put on a lot of miles; I don't own an engine hoist, though could probably borrow one; and of course, less $!

I've rebuilt engines before, but never just replaced a piston in the vehicle like this. For anyone who has, how did it turn out? Any thoughts are appreciated!
 
You can rent a hoist at most rental yards. I would have the head gone through and do a rebuild or just find a used replacement if it were me. I don't think just replacing one piston is a good idea. More pistons could be cracked and you would never know.
 
I've never replaced one piston, but i once re-ringed a suzuki samauri with the engine in the vehicle. If you want to avoid pulling the engine i think i'd replace the piston and the rings on the other 5. Since you have it apart. Also give you a chance to examine the other pistons. Thats a really durable engine and a piston coming apart is odd.
 
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You can always start pulling all pistons out and messure all 6 and compare them to factory data and max wear data. If the 5 pistons not harmed are within data there will be no problem just changing the rings.
 
I agree with bvance554. Whatever condition caused a piston skirt to crack and break was probably not limited to one cylinder, so I'd be cautious and at least check the other 5. Hopefully they will just need a re-ring. While the head is off get a valve job and then stick it back together. This is if you have enough time. Else I'd think about another engine. Good Luck!
 
You can do just one piston. There's no telling how long till another one breaks as this is fairly common on the 4.0. Don't forget to hone the bore and clean the crank well before putting the rod back on.
 
Originally Posted By: bvance554
I've never replaced one piston, but i once re-ringed a suzuki samauri with the engine in the vehicle. If you want to avoid pulling the engine i think i'd replace the piston and the rings on the other 5. Since you have it apart. Also give you a chance to examine the other pistons. Thats a really durable engine and a piston coming apart is odd.


You would think so but 4.0 pistons crack more than you think. Somewhere along the line mopar changed the design or something. Cracking a skirt is somewhat common though. Seems like the problem is commonly late 90's early 2000's

I would probably just get a used engine. The skirt could have damaged the cylinder or other stuff since it traveled all the way to the pan in pieces.
 
You already know what the right way to do the job is. I guess the real question is how long do you plan on keeping it, and is it worth the risk of another piston failing? Once you open it up and inspect it your decision should be easier.
 
Do you have all summer to mess with this, since it's your winter vehicle? If so, I might be tempted to pull the head, and pull all six pistons. If the inside of the motor is trashed, you could rent a hoist and replace with a junkyard motor. Or if its not trashed, replace the pistons and rings and put it back on the road for minimal cost, while being able to say you rebuilt it yourself.

Pulling the engine is probably the easiest and fastest, but I'm not sure about the cheapest. I don't know how much of a core charge there is on a junkyard motor, nor if your engine would be suitable for a core anymore--I'd ask. And then ask if they'd take it after you pulled the head off and the six pistons. If the don't care, you're out nothing by disassembling your motor. IOW, you could go down the path of piston replacement, and then if you throw in the towel, have lost nothing (it was a broken motor in the first place, after all).
 
Originally Posted By: Chris142
You can do just one piston. There's no telling how long till another one breaks as this is fairly common on the 4.0. Don't forget to hone the bore and clean the crank well before putting the rod back on.


Yup. A friend of mine cracked a piston skirt in his 2001 Wrangler. He bought an engine and just replaced one piston and bearing ... it still knocked.



Originally Posted By: robshelton
I agree with bvance554. Whatever condition caused a piston skirt to crack and break was probably not limited to one cylinder, so I'd be cautious and at least check the other 5. Hopefully they will just need a re-ring. While the head is off get a valve job and then stick it back together. This is if you have enough time. Else I'd think about another engine. Good Luck!


It's a 96+ 4.0 ... they enjoy tossing piston skirts.
 
The Good, the Bad and the Ugly -

The Good. About 15 years ago, my brother had a jeep with the inline six. Number one piston went bad. He replaced the number one piston and drove the vehicle another 50,000 miles with no problems and finally sold said vehicle.

The Bad. About 20 years ago, I had a 1968 International Pick up truck with the straight six. Cylinder number three always burned a huge amount of oil and constantly fouled the spark plug. I thought it might have broken rings, so finally dropped the oil pan and discoveredd pieces of the piston skirt in the pan. Like yours, the piston skirt on the number three was gone. I pulled the other pistons which revealed ALL piston skirts were cracked. I towed the truck to the junkyard and sold it for scrape.

The Ugly. Have you ever seen a 1968 International?
 
I have a reman engine in my Jeep as a piston skirt let go and caused the engine to completely fail.

Can't you drop the oil pan and pull the head without pulling the engine? Then you can remove the piston after reaming the ridge?

You will need to see the condition of the cylinder wall to see if its gouged. If so another engine or have the engine rebuilt (boring the cylinders).

The position of the rings moved in some manufacturing year and that allows for more wobble when the mileage gets up there. That is what causes the cracked skirt.

A reman engine is pretty reasonable at RockAuto.
 
If you are going to open it up you might as well do all new pistons, rings and have the head sent out and a decent valve job done. Do new crank bearings and any associated seals as well. Then you will have a reliable engine.
 
Originally Posted By: Doog
If you are going to open it up you might as well do all new pistons, rings and have the head sent out and a decent valve job done. Do new crank bearings and any associated seals as well. Then you will have a reliable engine.


I have two thoughts on this idea:
1) The wear in the cylinder walls is likely to cause more failures and the cylinders need to be bored.
2) New pistons from another company are not likely to have the same problem.
 
i would absolutely NOT waste your time fixing one piston. rebuild the thing and dont worry about it 2000 miles from now when the next one blows.
 
I guess the big question would be, what does the body look like? If you've got body rot going on, I would go as cheap and easy as possible. You have to remove the head for the one piston, so the other pistons will pop right out and you can give them a once over. If they look good, I'd slap on a set of rings and pop 'em right back in. While they're out and the pan is down, it would still be a good idea to at least replace the rod bearings.
 
Thanks guys, appreciate all the advice. I will pull the head and go from there.
 
Post pictures
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I would only buy a reman engine, or take the existing engine to the local automotive machinist and have everything done, including reboring all cylinders and having oversize pistons fitted.
 
I thought these engines were "unkillable"
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Failing piston skirts don't strike me as the mark of an "invincible" engine.
 
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