Uh Oh... cracked cylinder head!!

[NeXJ]

UPDATE - advice please...(?)

Okay, so the head was torn down by the mechanic (I'm going to look at it tomorrow) and he told me that No.2 cylinder was badly scored (I thought the cylinders were in the head - well what do I know...?) making the block kind of useless (according to him).

So I'm kind of skeptical that ALL is lost... what would YOU do in this kind of situation?

I'm thinking the scoring is unlikely to have come from the overheat. Is that even POSSIBLE???? And the compression was FINE before the overheat. So, in that case - would it even MATTER whether or not No.2 was dealt with (re-bored, etc.)?? And if I DID choose to deal with this - can you re-bore or ream the single cylinder and throw on a larger ring to compensate?

Anyway, I guess I'm just wondering what you guys suggest in this scenario.

Thanks alot,
Jonathan

 

[Eagle]

So... (okay here's where I demonstrate my ignorance) replacing the head alone will not suffice...? Are you saying I should replace the pistons themselves also (the piston RINGS are part of, or sit on, the pistons directly..? or am I mistaken?)...

I'm saying that you should not rush out to buy a head without doing a bit more investigation to determine what's wrong with the engine. A replacement head would be a waste of time and money IF the rings have been cooked.

I don't know how the mechanic could determine the head is cracked by doing a compression check. You didn't post the numbers, but I assume he got really low readings on two adjacent cylinders? A cracked head could do that -- and so could a blown head gasket. How are the compression numbers on the other cylinders?

 

[NeXJ]

I'm saying that you should not rush out to buy a head without doing a bit more investigation to determine what's wrong with the engine. A replacement head would be a waste of time and money IF the rings have been cooked.

I don't know how the mechanic could determine the head is cracked by doing a compression check. You didn't post the numbers, but I assume he got really low readings on two adjacent cylinders? A cracked head could do that -- and so could a blown head gasket. How are the compression numbers on the other cylinders?

Thanks Eagle, especially you and also sidriptide and dellstopjeep and others for your helpful input and opinions. If there is ANYONE unlikely to trust a mechanic it's probably me - I've been doing ALOT of my own wrenchwork for a few years now and that's saying alot as I have almost zero natural ability - any work I do tends to be accompanied by scraped knuckles galore, hooting and hollering and thrown wrenches (that'll teach 'em!!!) - so the very fact that I do it myself is a testament to my hatred of the mechanic types. But I just do NOT have the time or the facilities to do this right now, despite having an okay selection of tools.

ANYWAY, so the UPSHOT of what I'm trying to say here is that I found a mech (not jeep specialist) who I trust very much - I had him previously attempt an install of a temp sensor (to adapt a 98 engine in a 92 XJ) which was unsuccessful but ambitious which he did not charge me for despite the four hours of labor. So that earns some trust.

The assessment of the cracked block came from the teardown he did. (thought I mentioned that!) - he told me there was a "big old crack" between 3 and 4. I told him to press on and remove the head and see what he thinks of the possibility of a head swap and he told me that cylinder 2 was pretty badly scored. ANYWAY - the whole thing is currently apart and I'm going there to have a look for myself tomorrow AM. Should be interesting. I'll be sure to collect the compression numbers and post it here afterwards. I'm just trying to figure it all out. The mech told me I COULD swap the head and any other pertinent parts - but at my own risk - that I'd probably burn lots of oil due to #2. So that's why I'm on here - for a 2nd opinion. Right?? What I STILL don't really get (directed at you, Eagle) is why the piston rings are such a problem... is it because the pistons/engine would need to be totally rebuilt in order to fit new rings properly?? Let me know if you can - but I'll still hit you guys back with my inspection results tomorrow.


Jonathan

 

[MudDawg]

Ok...on the rings...get 'em too hot...they don't seal anymore. They will lose their tension. If you run a motor with bad rings, the is an escalation of damage..oil will carbonize the rings into the ring lands rendering them absolutely useless. If the block is cracked...it's a paperweight now..if the bores are scored...the pistons are toast too...aluminum melts at a LOT lower temperature than cast iron. Visual clues...a blue colored bore means it's been hot...a scored bore, especially if there is aluminum embedded...completely toast...Any of this damage can be repaired but the cost will be very high.

Best bet is to score a good used motor....the hardest part of changing an engine is the actual removal process...you can go to a rent-it shop and get an engine lift for a day for cheap...scare up a couple of friends, a case of brews and some snacks...can have it done in a day...XJ's are amazingly easy to work on compared to most other 4x4 vehicles.

 

[NeXJ]

Thanks for the info Mud Dawg.... I'm feeling like more and more of an ass for neglecting my coolant leak (I was kind of tired of dealing with replacing hoses, etc....). Guess I paid the price!! I didn't know it (the leak) was that bad. So anyway, it's looking more and more like I'm going to do my second engine swap... crap!! NOT fun.

Anybody know if I'd be able to fit a '94 HO 4.0 from a ZJ into my XJ?? I've got a line on one for $500.

Jonathan

 

[sidriptide]

from what you've said the mechanic "told" you, it sounds pretty much on-the-level... before teardown he said probably a cracked head.. i agree.... after teardown and better inspection he says a cracked head and a badly scored cylinder.. sounds almost texbook to me also... if you trust him it doesnt sound like bad info to me... as muddawg stated before.. there is no chance of ingoring a bad cylinder and driving it like it is... i have a question for you now.... have you asked these questions to your mechanic directly? these will basically be the same answers he gives you.. and he will be able to give better answers strictly from his hands-on inspection of your engine... we can try to point you in the right direction and give you the answers "we think " you will hear and try to keep you from getting "taken " on the job.... at this point i would look at the ZJ engine as a swap... the actual engine should be indentical but i am not sure about the accesory pulleys and bracket.. which will easily be swaped from yours.... before you buy a used engine insist on a compression test and have the mechanic look at the numbers... good luck on this and chalk it up as a lesson learned in basic maintenance and how not to ignore a "small " leak...
mike

 

[Eagle]

I second what Sidriptide said

 

[jkmhb]

My son's '95 overheated and had a bad miss afterwards - low compression #1 cylinder. I pulled the head and #1 and #2 had aluminum deposits on the cyl. walls from scoring.

A Craftsman hone cleaned up the cylinder walls, rebuilt guaranteed head from Autozone ($160 exchange), 2 pistons, rings, conn. rod bearings from Kragen, new GDI 3-row radiator ($135 at Autozone).

Under $600 total and it runs great with no overheating problems and passed smog with flying colors.

Death to the junk single row radiators.

 

[sidriptide]

just for the sake of asking.. this "ghetto rebuild" was at least done with the engine disassembled wasn't it? not that "ghetto" is bad.. thats probably what i'd do with my trail rig before i give it a new engine...
mike

 

[jkmhb]

If you're talking about my "ghetto rebuild" - no, it was done with the motor in the car with the head and pan off. Careful placement of rags and taped passages and taped crank to block out the debris, and a lot of cleaning afterwards. A quick oil change after the first start and it's going 1500+ miles per quart on a 111K motor.

 

[sidriptide]

good deal on saving that engine.. just goes to show that sometimes the cheap way will do it just as well sometimes..
mike

 

[NeXJ]

Yeah... okay - this thread is actually pretty timely for me... I'd like to hear more about the 'ghetto rebuild'. I went to the shop to have a look at the torn down engine. Supposedly the number 2 cylinder was 'really badly scored' - though it REALLY does NOT look all that bad to me. Guess I'm not used to the precision work involved in the world of engines. I mean - I had a good feel around inside the cylinder - and couldn't even begin to FEEL the score with my fingers. You could see it - but I find it hard to believe that honing wouldn't be enough...

so here's the question... If I DO go this route... should I get the cylinders honed and throw on new rings, etc... ? What else? Should I try it myself??

Must be a HELL of a job getting the pistons out (I'm assuming you have to remove the crankshaft - which would involve removing the engine first??)

Anybody want to tackle this?

thanks profusely,
Jonathan

 

[5-90]

You have to pull the pan to get the pistons out, but they come out thru the top - therefore, pull the head as well.

The 4.0 (especially the AMC-Spec - 1987-1990) uses a high-nickel-content iron alloy. When I pulled my 87 apart at 220K, there was a measured .001" total of ridge (so .0005" high!) at the top of the cylinder - which was quickly handled with 180-grit stones. Don't be surprised if you get in there and there's not enough ridge to feel - if you keep it oiled, you won't have much and a quick stoning will be all that is necessary.

It is not strictly necessary to pull the crank to do pistons - you just need the pan out of the way so you can get a broomstick section (preferred tool...) under the piston to push it out the top. If you are working with the engine in place, I suggest having a helper play catch with the pistons so they don't pop anywhere when they come free (this is not skilled labour - anyone who can follow instructions can handle the job.) The only real crank issue with pulling pistons is that you will want to put some rubber hose over the rod bolts before you push them, so you don't accidentally score the crank journals. Buy plenty of hose, and just leave it on until the pistons go back in. Oh - make sure you mark the big end caps before things get mixed up - even production rods are made from a single piece of alloy, and you don't want to mess up your bearing clearances...

A Scotch-Brite wheel, gently applied, is THE thing to clean piston heads. In the event you don't have access to any (I can get them at the local hardware store and the local parts house, so they're not that hard to come by) and brass wheel brush is absolutely the most aggressive thing I care to use on a piston - and that with great care. Use Scotch-Brite on the head and deck mating surfaces, and you can use a brass brush on the combustion bowl as long as you don't get happy around the valve edges (leave the valves in for this treatment...)

Oh - and if there's no ridge, the pistons will just push right out. The only thing holding them in the bores once they're unbolted and free will be ring tension...

Any other questions?

5-90

 

[jkmhb]

Mine had heavy aluminum deposits on the cylinder walls #1 and 2, but it cleaned up really nice with a 3 stone hone (well lubed with trans. fluid). When done, maybe one real small scratch that you could bearly feel with your fingernail. The pistons were toast, and the valves did not seat on #1 due to aluminum deposits there as well, hence the loss of compression. Connecting rod bearings on those two showed some wear, probably from the aluminum also.

The bores need to be cleaned really well with lint free rags (I used laquer thinner with them) to get all the metal grit out from the honing.

All this from one overheat.