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Unread 02-05-2012, 04:55 PM   #1
JeepJon15
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4.2 yj engine knock, cracked head?

I just posted a thread today with questions about a spring lift, but it looks like my saved money is going towards my newest problem.

i have an 88 4.2 auto.

A couple days ago i put a half qt of oil in to top off, and it seems i left the oil cap off. Today i stop at the gas station, when i go to pull out the engine has a quiet knock, which gets much louder when i accelerate so i take the first right 10 feet down the road and park it, as a large puff of smoke flows from the jeep.

So it only knocked for about 10 seconds before i shut it off. I put some oil in and got a ride to my local autoparts store for a new oil cap. After i got oil in it and the cap on i tried it and, surprise surprise, the knock is still there. When i push the gas oil comes out of a small hole in the exhaust just under the manifold.

I asked a mechanic friend, he said let it completely cool down and there is a slim chance it will run normally, but if problem persists its likely a cracked/warped head.

What is my best course of action here? I want to keep the jeep, so do i rebuild? replace? I'd like to do it myself, i have people i can get help from. Also, i dont have a lot of money but i have about a grand put away.

I'll try and start it in a couple hours and hope for the best, but being realistic i expect i have a major project ahead of me.

Thanks for any suggestions.
Jon.

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Unread 02-05-2012, 06:47 PM   #2
jay-h
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So oil is actually coming out the exhaust?

It's a little unclear what is going on. Pulling the head is a start, it's not that hard. The rest depends on what you find. If you do simply have a cracked head or head gasket, that's a straightforward fix.

If the engine is bad, my personal choice is to get a re-man from a reliable rebuilder. You get what is pretty much a new engine, and don't have to fuss with fixing yours or (perhaps) finding more problems once you open it up.

The cheapest fix is a running junkyard engine if you can find one, but unless your budget is strongly limited, I'd stick with the re-man.
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Unread 02-05-2012, 07:56 PM   #3
Old4X
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Where is the knock coming from exactly?

High on the engine, low, front, rear?

Your smoke probably came from the oil spill.

Loss of oiling rarely causes head damage, bearing damage is most likely. This is why it is important to locate knock location.
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Unread 02-05-2012, 10:23 PM   #4
JeepJon15
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Ill narrow down where the noise is coming from tomorrow.

And yes the oil seemed to come out of a hole in the exhaust after i put oil back in it and revved the engine a little.

Today was a busy day so after i had her toed back i didnt have much time to look at it. Ill have some better info tomorrow.

Thanks guys.
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Unread 02-05-2012, 10:24 PM   #5
JeepJon15
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Ill narrow down where the noise is coming from tomorrow.

And yes the oil seemed to come out of a hole in the exhaust after i put oil back in it and revved the engine a little.

Today was a busy day so after i had her toed back i didnt have much time to look at it. Ill have some better info tomorrow.

Thanks guys.
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Unread 02-06-2012, 12:49 PM   #6
JeepJon15
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Reporting back. I just started it, and it still starts fine, but the LOUD knock is still there and it smokes a little bit with a smell that seems to have both oil and coolant in it.

From what i can tell its coming from the middle to rear of the engine, seems louder toward the passenger side. It sounds really bad so i dont want to run it for more than a minute until i'm instructed otherwise.

I've thought it over, and it turns out it wont kill me if i have to get rid of the jeep. Though if i do another is in the near future. Before this problem, i was saving to redo the suspension, so its not like once i get the engine together im good to go. Basically if its 1000+ to get it running again i have to wash my hands of it; its my daily driver and i cant afford to have her in the garage long enough for me to learn to rebuild an engine.

Without taking the engine apart, is there anything else i can give you guys to help diagnose the problem?
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Unread 02-06-2012, 01:10 PM   #7
lobukjeep
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Did you check to see if you had coolant in your oil?You could have popped a head gasket dumping coolant in your oil which in turn could have wiped a bearing.Causing your rod knock.At least from reading it sounds you might have a rod knock.Here's what you can try.Apply park brake Start Jeep.Pull #1 plug wire off(without getting shocked).Did the knock lessen?If not,put wire back on.Go to #2 wire do the same thing.Do that for all cylinders.Eventually you will get to the cylinder that i am guessing has the rod knock.When you get to the cylinder that has the rod knock and you pull the plug wire off it will get noticeably quieter."IF" it does that then you know that you have a rod knock and what cylinder it is.Then you know what your dealing with.
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Unread 02-06-2012, 01:31 PM   #8
JeepJon15
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Ill try that, but it will take a minute to check all the plugs. Does that mean i probably wont be doing any more significant damage by letting it run?

Ill be back with more info shortly.

Thanks
Jon

edit: thought id mention that i have ever seen the thermostat get above normal. It went from running like usual to the knock with no in-between.
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Unread 02-06-2012, 01:43 PM   #9
JeepJon15
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More info, as promised. Now it wont start.

It turns, and i hear the knock as it turns but i cant get it to fire up.

I know there isnt much to go on here. But any advise you guys can give me would be awesome.

Is a 1000 dollar budget to small to get it running again? Like i said before, i dont have the luxury of slowly fixing it, its my daily driver. Scrap it? Sell it? Part it? Or can it be fixed without breaking the bank.

I love the jeep, but i need something to get me to work and back every day. (6 miles each way, not far).
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Unread 02-06-2012, 04:07 PM   #10
lobukjeep
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6 miles??? I think i could Huffy that if it meant scrapping my jeep.But in all seriousness it depends how much work you want to do.It's definitely doable with lots of change to spare if you do the work yourself.The hard part is diagnoses.Good diagnoses will save you tens of thousands in your life time.Well i would start with the basics.It cranks but no start now??Find out if you have lack of spark air or fuel.Chances are you have air.So spark or fuel could be the culprit.If you have both of them then you have a more complicated problem.I would do a compression check.Pull your spark plugs out one by one.See what your plugs look like.They can tell you a lot. But like i said ...start basic. and let us know what you find.
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Unread 02-06-2012, 04:09 PM   #11
JeepJon15
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Update. I pulled the oil pan and looked around. When i started poking around cylinder #3 some coolent trickled out. This lead me to look INSIDE the oil pan which i had pushed aside. What looks like a portion of the 3rd piston is in pieces in my oil pan.

So i'm pretty sure i've found the problem. Where do i go from here? I've never done engine work like this. So keeping my budget in mind should i dig in, or have someone else dig in? I really dont mind doing work, but i cant be working on it for weeks.

Poor jeep...


EDIT: Lobukjeep: I do huffy it sometimes in the summer hah. But still, point is its my only vehicle... your wisdom please?
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Unread 02-06-2012, 04:49 PM   #12
lovett86
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if its just the piston then u can put a used one back in it, but take a look at the cylinder walls for scoring and damage and take a look at the rod bearing for damage, your gonna have to pull the head off to put a piston in it, also take off your oil filter and see if it is full of metal
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Unread 02-06-2012, 06:56 PM   #13
Peter Nuss
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Buy a camera, take pictures of what you found and post them. You guessing what you have and everyone else guessing what you mean is not the best way to diagnose a problem. If you have coolant in the oil, you have a bad head gasket, or a cracked head or block. No other reason for coolant in the oil. If time is really a problem, just buy a junk yard engine with a warranty and switch them out. Don't bother looking for the problem it will only waste time. You could buy a 4.0 put a carb on and drive it.
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Unread 02-06-2012, 08:10 PM   #14
Old4X
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Quote:
Originally Posted by Peter Nuss View Post
You could buy a 4.0 put a carb on and drive it.
You can do this cheaper than fixing what you have.
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Unread 02-06-2012, 08:22 PM   #15
laybackman
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You detonted a piston on a motor that is 24 yeqrs old and has had how many cowboys beat on it, and it just detonated a pistin? That cylinder is already completely worn out and now it most likely has a deep gouge in it from that pistion ping-ponging around inside it's cylinder. My guess is you dewswtroyed that cylinder wall beyond repair and also possobly cracked the cylinder wall, hence the oil and anti-freeze cocktail.

Now even if this motor is salvagable which I'll bet it isin't, do you have the skills to pull it out take it apart get it rebuilt re-assemble it then tuck it back into your YJ?

The best adivce was already given IMHO, spend no $$$ on this engine but upgrade to a newer 4.0

I would not spend a dime on that motor.
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