ramcharger
Dismember
This piston came out of my 4.0L HO Jeep. In all my years as a mechanic, I've never seen a piston damaged like this. The top ring is gone completely, not a trace of it exists. It's as if it had dissolved.
Major Piston Damage!
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Wylde1
"No Value Added" Member
That's a mess! How bad is the cylinder?
Wylde1.
Wylde1.
ramcharger
Dismember
I think a .060 bore will clean it up. There's a depression that matches up with the part of the missing piston top that needs to be cleaned up, but the cylinder isn't near as bad as it should be.
I knew this thing needed rings but this was an unpleasant surprise. Believe it or not, it really didn't run that bad, lol.
I knew this thing needed rings but this was an unpleasant surprise. Believe it or not, it really didn't run that bad, lol.
ramcharger
Dismember
The porcelain was cracked off on the plug too. I don't know if that was the cause of this problem or an effect.
Mopower71
Speed Demon
How much nitrous were you throwing at that?
Is it possible the plug was loose?
Is it possible the plug was loose?
ramcharger
Dismember
Detonation came to mind to but it's naturally aspirated, fuel injected and computer controlled. This is the only cylinder that has this problem. All the rest were OK. They needed rings but the ridge was very minimal.
This project has just gotten expensive. This was just supposed to be a quicky re-ring and lifter job.
ramcharger
Dismember
LOL! It sure looks like a nitrous destroyed piston, doesn't it? Nope, no N20 on the Jeep.
The plug was tight when I checked it. I'm wondering if it had a bad injector causing it to lean out on that cylinder. I checked the records that the previous owner had given me last December. It was brought in at 200K for a "rough idle" issue. The dealer installed plugs, cap and rotor and wires, cleaned the throttle body and checked fuel pressure. The mechanic stated that it still runs rough and further diagnoses was necessary. As far as I know, this was the last time the plugs were changed. It has 223K on it now.
This Jeep has a massive class IV hitch on it. I wonder if they just flogged it to death in the mountains here while towing a motor home and without shifting down and on cheap gas. The rear springs are sagging bad too. I'll check that exhaust valve tomorrow and see if it's bent.
pettybludart
Well-Known Member
It might be cheaper to just find another motor out of a wreck?Just a thought.Good Luck!
demon seed
The Original Demon Seed
Hard to say if it was to lean, all the oil that piston was passing kind of mudles up the color issue, white exhaust valve is normal. Could have just been a faulty piston.
Terry
Wow.....sorry to hear this ramcharger. :scratch:
I hate opening "cans of worms", but glad you found the problem with the Jeep and am confident you can make it right. :thumbup:
I hate opening "cans of worms", but glad you found the problem with the Jeep and am confident you can make it right. :thumbup:
ramcharger
Dismember
I'm going to look around tommorow for a short block. I know a guy in town that has 'em for about a $100. Hopefully he's got one. I actually put money down on one right before I got laid off but cancleled. I sure as shoot wish I had it now.
10-4 on the oil issue mucking up the color. I suppose it could be a faulty piston Terry. I'll clean all the mung off it tomorrow for a better look at what happened here. The mystery deepens... :-D
OK, I was just thinking that it's possible that a sensor such as the TPS sensor had gone bad and the previous owners just continued to drive it. This would cause the engine to receive too much timing from the computer. They had it replaced eventually but by that time the damage was done. What do you all think? Likely scenario or pissing in the wind?
Yep, not quite what I expected to find. That piston dropped right out of the bore, lol. The good news is that I caught it before the block and crank went to scrap. The cam chain had 4 degrees of slop, the upper rod bearings were down to copper but not the lowers and the cam was getting ready to self-destruct. The main bearing and rod journals look pretty darn good. :cheers:
OK, I was just thinking that maybe the previous owners had a sensor like the TPS go bad but they just kept driving it. This would cause the engine to receive too much timing. Eventually, they had it replaced but by that time the damage was done. What do you all think? Possible or just pissing into the wind?
magnumdart
There is a bad moon on the rise.
Just got done putting a new engine in a '92 Laredo. Same thing wrong with piston in the original. Made noise forever but kept running. I did everthing to that engine to try to stop it from making noise including new rockers on the bad cylinder, new cam, new lifters, cleaned all the pushrods. Finally a small part of the piston lifted enough to hit the head and it really started to pound. That was it for it. It made noise when I bought it at the start of our sons college and lasted through his masters before it let loose. I usually associate the 4.0 as a good engine as our other '92 went 317,000 before we just burned out on drivng it and gave it to one of our daughters. It still got 18.2 mpg, same as new, and never used any oil. I changed the oil in it 109 times, and the rear seal every 100,000 to 120,000 miles because of leaks. If I remember correctly it was number four cylinder that had the bad piston.
retsud_043
Well-Known Member
Ouch#-o That's something you didn't need to see Joe:sad1:
I'm workin' on a guy's Cavalier that he just bought. He dove it for a couple hundred miles and noticed he was losing power.
I told him that loose spark plugs like to make holes in pistons:angry7:
I can pull off the oil filler cap feel the suction and pressure from the two cylinders:toothy10:
I'm workin' on a guy's Cavalier that he just bought. He dove it for a couple hundred miles and noticed he was losing power.
I told him that loose spark plugs like to make holes in pistons:angry7:
I can pull off the oil filler cap feel the suction and pressure from the two cylinders:toothy10:
ramcharger
Dismember
Yep, this was the #5 piston and it is a '92. It actually didn't run all that bad really and I was thinking that the noise was a collapsed lifter. It did have some blow by so I figured I'd just pull the sucker and do the rear seal, re-ring it and seal up the oil filter adapter and check the bearings. I am impressed that the cylinder wall took a beating and looks really good for what it went through. The crank looks damn good too for 225K. I wonder if Terry is right and they just had some bad castings?
ramcharger
Dismember
Wow!
magnumdart
There is a bad moon on the rise.
I never did try to figure out what the problem was. Just junked the engine when I saw the damage to the top of the piston. Could have been a spark plug problem,or maybe even a ring gap (too large or small) problem. Don't know, but I bet someone on here may have a little more imput for you so it doesn't happen to you again. Just so you know, the 4.0 head will fit the earlier carbureted models with a major gain in hp, if you go the short block route and find an older one. Who knows, they may even be less money. Just do a little research on it to make sure you mix and match correctly.
ramcharger
Dismember
That thought did run through my head, lol!
Man it sure would be interesting to find out what it was. I'll keep poking along until I find a clue...
Good news! I just got in touch with one of my Jeep cohorts from NAXJA.com and he's got a '93 he's parting out with a 4.0 HO that runs great but it is high mileage. Compression is 150 across the board. He'll let me have it for 100 bucks but I have to pull it. I can now box up my engine for a future stroker build. :cheers: I'm just glad to have the foresight to not order parts until all my ducks are in a row. A high mileage engine is like a box of chocolates, lol. :-D
camd64
Remember Landy
wow, talk about FUBAR'ed! the mysterious disappearing piston ring.
grumpuscreature
Resident Curmudgeon
Now you know what was causing the knock. Amazing what kind of damage they will run with.
ramcharger
Dismember
That ring is what has me baffled. Possibly hot combustion gases ate it up when combined with oil? Maybe an acid was formed?
Yep, that part of the mystery was solved. It really sounded more like a bad rocker, pushrod or lifter. It also explains the oil consumption (a qt. every 200 miles) and the blow by.
It really was amazing that it ran as well as it did. That sucker really did get up and go when merging into traffic. One more month or so of driving it like that and I would have ruined the block and crank though.... :read2:
74scamp360
Junior Member
wow that's buggered up bad, good luck on the rebuild!!
ramcharger
Dismember
I know a local guy here who has a business parting out Jeeps and he has a high mileage engine that runs good, but I have to pull it myself. We've already agreed on a very, very reasonable price for the whole engine so I'm just waiting on a date and time to run over there and pull it. :cheers: The engine with the bad piston will be bagged and tagged for a later stroker build. :-D Like many on here have already said, an AMC crank and rods from a 258 I6 will drop right in and give me a 4.6 L HO. :-D Some machine work will be required to fit the stock damper and it should be balanced too.
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