ayoung16

So I was hearing a ticking/rattle, from where I thought was coming from the bellhousing. So I took it to jeep guy that knows them in and out to check/ replace flex plate.. We'll as the title suggests, it's a broken piston skirt and in way related to the torque converter or flexplate. The 4.0 has 185k miles and runs fine and strong, just tick tickie ti tick tick at idle... The jeep guy said, "just drive it dude, it will run forever like that". So my question is who else out there has or is dealing with this and any thoughts or concerns that go along with it.

Turbo X_J

"The jeep guy said, "just drive it dude, it will run forever like that"."

Sure why not he won't be the one stranded when the engine finally gives up, sounds like it's time for a rebuild.

peep

A broken piston skirt is a roulette wheel.
The odds are stacked against you.
We're all "the jeep guy" and we know them inside and out, we all have our opinions and we are not always right.
There is no wishing it right. Turbo giving it to you straight.

bigbadon

How did the mechanic confirm that it was a broken skirt? Was that his opinion or did he drop the oil pan and look?

F1Addict

The tick you hear is the piston rocking back and forth within the cylinder bore. It will eventually score the bore and require a full engine rebuild including cylinder honing. On the other hand, you can replace the piston now, before much damage is done, without having to pull the engine.

At the very least, drop the pan and pull the bits of skirt out of there so they don't get pulled back up into the crank.

ayoung16

Stethoscope, trained ear and experience with his personal 4.0s. He's older and more experience than myself plus he builds woods jeeps and is a friend so I mean yes people have opinions and very we'll could be wrong but I don't think he is out to get me, ya know. He was saying just drive it till it has no power and burns a lot of oil then rebuild. Tho I do agree with turbo that a rebuild will be in the future, since it runs fine and has more power than the other 4.0 tj I've owned I can't just stomach rebuilding right now. That's what got me so torn is that it runs beautifully other than the piston slap. I appreciate y'all's input was just wondering other experience with this problem and thoughts.

Turbo X_J

If the piston locks up in the bore & kicks the rod through the block the rebuild option is off the table.

peep

I don't mean to imply your friend was trying to steer you wrong. Some additional investigating is required to get confirmation on the multiple possible / probable cause suggestions on the table. The ticki could even be an exhaust leak? At 185K your engine is worth taking care of. Mines got three times the mileage and yes it has multiple noises. Multiple noises like me, I'm old too, and I'm wrong lots. The stethoscope is an excellent tool for investigation. Plan to spend some time investigating to find the true cause, don't run hard in the meantime. If it is a failing piston then final failure will be catastrophic. Hope you find a lesser reason.

Radi

Pull the pan and look. Mine was a cracked skirt that would surely have turned into a broken piston down the road.
The noise difference between cracked and broken is large, BTW. Broken skirt sounds like a chunk of sheet metal in a bicycle spoke. Thwak wak wak wak. You can't miss it. Problem is one day the first will turn into the second with no warning.
You could replace the weak piston in less than a day at minimal cost and put the full rebuild off for an indefinite period.
If you can remove and reinstall the head you can do the piston swap.

ayoung16

I will be pulling the pan tomorrow at the shop. And more than likely replacing the piston. Thanks for the input

5-90

1) It's not a piston "skirt" - it's a piston kilt! The AMC engines are pretty much the definition of "manly." Manly men don't wear skirts, but they have been known to wear kilts... (Me wife sez I look good in mine - Ross & MacLeod...)

2) I'd get a semi-rigid borescope (if I could,) you want it to be 24-36" long and have a head smaller than 0.480" (7/16" would be about the outside.) That way, you could snake it up through the sump drain at your next oil change and see just how much of it is broken - if you're lucky, you can hook it down and see the broken piece. If not, hook it up and check each cylinder individually. That will allow you to check and see which piston lost a piece, and how much (compare one side to the other.)

3) If the broken bit is less than an inch or so long, you'll probably be fine. The pistons are cast aluminum, so the iron cylinder walls will help to burnish the broken edge and cylinder damage should be minimal to non-existent.

The 6-242 is a relatively low-compression & low-RPM engine, so piston rocking shouldn't be a big issue for a small break. I'd just want to visually check it - but I'm funny that way...

DFlintstone

Boy, in some company I might seem to know a bit about engines, here I feel like a tadpole! Radi actually ran his original rings when he changed pistons to make it another ...bit. Anyway mine has been making a good rap for over 100,000 miles and 12 years. Partly why there was a good price. This it's at it's worst, in cold an hr after being hot. About 276K. Lifter maybe.

I'd do a wet/dry compression test before I pulled anything apart. Anyway here's mine

bigbadon

Common sound for alot of 4.0s....some more subtle. Not exactly sure what it is ( piston slap usually quiets down as engine warms). Mine has a had a similar sound but not as loud and 4 psi oil pressure for years. Mine has become a quest to see how far it can go and when and if it does blow I'll just drop in a new motor. I agree with your mechanic,"just drive it".

PocketsEmpty

you can't be sure it's a broken piston kilt unless you drop the pan and look. Plain and simple.

Good luck replacing it! you'll be happy that you did....if that's ultimately the issue

ayoung16

Mine sounds exactly like lintstone's clip... To a tee... As close as it could be over a YouTube clip

Finally I hear some sense from non doom sayers (no offense we all have our opinions)

I'm going to drive it till it takes a crap and when the next oil change comes around I'm going to pull the pan and check for bits and pieces.
And probably unless there is a giant chunk down there, keep on driving it.