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Unread 05-06-2013, 11:33 AM   #1
AVR2
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Check these pics and tell me about my cylinder head and piston bores...

Here are some pictures of my just-pulled head and cylinder bores. I'm open to any and all opinions as to what they say as regards the condition of the engine. I've been burning oil on idle so the head's off for a valve job.

I'm particularly concerned with the half-centimeter or so at the very top of the cylinder bore. It's like it's got a lip of corrosion, it's dry and rough, while the rest of the bore is completely smooth and shiny (all the bores are like this). I just don't have the time or facilities to remove the block, so any repair work needs to happen with the bottom end where it is. Also, what's the flaky stuff on the piston top in the last picture? Evidence of oil burning?

One small thing of note - bolt #14, the one that you're not supposed to be able to get all the way out until the head is pulled forward to clear the cowl, just pulled straight up and out on mine. All the clearance in the world. I guess the earliest 1992-build ZJs are slightly different in that regard.

cylinder-bore.jpg   valve1.jpg   valve2.jpg   valve3.jpg   valve4.jpg  

valve5.jpg   valve6.jpg   piston.jpg  
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Unread 05-06-2013, 12:12 PM   #2
a70eliminator
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Looks like a typical healthy engine to me, maybe a little oil escaping the valve stem seals but nothing major, the ridge is totally normal as that last 1/4" is essentially part of the combustion chamber and will always have carbon build up like that.
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Unread 05-06-2013, 12:28 PM   #3
xcaliber81
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i was told that shiny cylinder walls is not particularly good and that is a sign of blow by.
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Unread 05-06-2013, 01:11 PM   #4
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Quote:
Originally Posted by a70eliminator View Post
Looks like a typical healthy engine to me, maybe a little oil escaping the valve stem seals but nothing major
The smoke on idle was very noticeable, and all the plugs are showing ash deposits consistent with burning oil. It basically failed its last inspection because of it.

Quote:
the ridge is totally normal as that last 1/4" is essentially part of the combustion chamber and will always have carbon build up like that.
Cool, so I don't have to worry about that? Just leave it? Or is it worth using emery paper or similar to get rid of the corrosion while I can?

Quote:
Originally Posted by xcaliber81
I was told that shiny cylinder walls is not particularly good and that is a sign of blow by
AFAIK I'm not getting blow-by (no oil in my breather).

A quick Google reveals that it's one of those automotive subjects that seriously divides opinion - some people insist that shiny cylinder walls are exactly what you want to see in a high-miles motor and honing is only necessary after a rebore, others insist that shiny cylinders always need to be honed.

The SAE's position, after extensive research, is that honing is completely unnecessary if you haven't rebored. See here for an article explaining why.
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Unread 05-06-2013, 01:12 PM   #5
zjosh93
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Shiny walls mean that the rings have worn through the original cross hatching honed in by the factory. It means the bores and rings are worn. Worn bores and rings are where you get blow by. You can measure the bores and pistons and if you are really lucky the amount of wear and taper will be close enough to spec that you can hone and rering. Or just hone and rering anyway, it won't hurt anything. The top ring sits about 3/8" down the piston so the top of the bores never get scraped. That's why there's varnish build up there. If you clean the top of the bores with solvent and there isn't a ridge worn into the cylinder big enough to catch your fingernail your bores are probably ok to hone. Everything else is normal.
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Unread 05-06-2013, 01:25 PM   #6
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I'm not going to rering, it simply isn't worth the time and money - I only need the ZJ to last me another 12-18 months. It only blows smoke on idle, consistent with leaking valve stem seals, and I'm not getting the typical symptom of 4.0L blow-by (i.e. there's no oil in my air filter).
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Unread 05-06-2013, 01:49 PM   #7
xcaliber81
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we are not saying you are getting blow by for sure. my dad is an hd mechanic and has been for 15+ years and that's what he told me shinny walls is not what you want to see. however with such a high mileage engine shinny walls is kind of going to be the norm.
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Unread 05-06-2013, 02:54 PM   #8
HighLonesome
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What I've seen with leaking valve stem seals is smoke at startup and then the oil burns off after a little while and then no more smoke.
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Unread 05-06-2013, 02:56 PM   #9
AVR2
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Did you read that article I linked to? That refers to an argument that broke out among professional mechanics when it was stated that honing was only necessary after a rebore. The Society of Automotive Engineers has researched it and its official position is now exactly that (the article explains the research that was done), but it's one of those subjects that strongly divides people. Me, I have no history here, so I'm going with the opinion of the SAE
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Unread 05-06-2013, 03:17 PM   #10
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Originally Posted by HighLonesome View Post
What I've seen with leaking valve stem seals is smoke at startup and then the oil burns off after a little while and then no more smoke.
If the seals are worn badly enough, you will see smoke returning during idle, as the increased vacuum pulls oil down past the seals into the combustion chamber. If I let my ZJ idle normally at traffic lights it starts smoking, but if I put it into neutral and then give it just enough gas to rev at about 1500, the smoking stops.
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Unread 05-06-2013, 03:25 PM   #11
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Quote:
Originally Posted by AVR2 View Post
If the seals are worn badly enough, you will see smoke returning during idle, as the increased vacuum pulls oil down past the seals into the combustion chamber. If I let my ZJ idle normally at traffic lights it starts smoking, but if I put it into neutral and then give it just enough gas to rev at about 1500, the smoking stops.
Sounds like you've done your homework. I guess I never had seals leaking that bad before. I have a one-cylinder motorcycle that has leaky seals and I just live with it. I have to let it sit for a week before it will blow smoke at startup.
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Unread 05-06-2013, 03:36 PM   #12
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Quote:
Originally Posted by AVR2 View Post
Did you read that article I linked to? That refers to an argument that broke out among professional mechanics when it was stated that honing was only necessary after a rebore. The Society of Automotive Engineers has researched it and its official position is now exactly that (the article explains the research that was done), but it's one of those subjects that strongly divides people. Me, I have no history here, so I'm going with the opinion of the SAE
The SAE paper makes a few key assumptions that may not hold true on a vehicle by vehicle basis.

First being that extended ring break in is acceptable. I've re-ringed without honing and am here to tell ya that 10K mile ring break in is the result. For any kind of low use engine (performance, weekend cruiser, etc) this just isn't acceptable. Nobody wants their rebuild smoking under acceleration when it's 2 summers old.

Second being that the perfectly smooth surface left by wear is ideal. The way that bore got polished was wear. If you start looking at used cylinders with a bore micrometer, a self-polished cylinder is an egg shaped cylinder that needs bored. You don't get to one wear characteristic without the other with the materials used for automotive cylinders & pistons.

The author has many good points about premature wear, but the hone does overcome several blind spots for the average home rebuilder. Don't be so quick to throw it away.

Generally speaking, when I use a hone, the voice in my head is saying I'm about to assemble a cylinder that's already 010 over by wear and I'm a cheap bastrd. Most people would be suprised at how much longevity you can get out of reeeallly loose pistons if they're not revved hard. Tight pistons will die tomorrow however.

fun discussion
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Unread 05-06-2013, 10:43 PM   #13
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Originally Posted by Foundrydude View Post
The SAE paper makes a few key assumptions that may not hold true on a vehicle by vehicle basis
Given that they did the research and the results were consistent across all the test vehicles, it would suggest that there's definitely something in it. I've since found some more testimonials from rebuilders who no longer routinely hone, and after seeing the results for themselves they support the SAE's position.

It's a moot point for me, since I only need to stop my ZJ smoking on idle so I can pass inspection and get another year or so's use out of it. For all sorts of reasons (not least time and money), bottom-end work just isn't on the agenda.
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Unread 05-07-2013, 03:53 AM   #14
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I had the same good fortune with my head bolts, no clearance issues. The flaky stuff you're seeing is loose carbon build up. It's normal. Since you have it apart, now is a great time to get rid of all that carbon. If you read through my head rebuild thread, you'll see that I did that using brass tools so I didn't gouge anything. The ridge ring is normal, just clean it off.
I'm not going to jump in this hone/no hone argument, but I will say that if the rings are holding acceptable compression, you'll be fine to run it as is. As long as you don't try a mile long burnout or any drifting, it'll last you the year or two you want out of it no problem.
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My cylinder head overhaul: http://www.jeepforum.com/forum/f13/cylinder-head-r-r-picture-heavy-1348138/
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Unread 05-07-2013, 04:17 AM   #15
Candymancan
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mm my 5.9's cylinders wall when i look through the spark plug holes are shiny.. guess im boned once my carbon breaks up.. compression is like 185 psi.. curious to see if i get blowby if my engine ever decarbons itself since i fixed my plenum
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