Little background on this engine. I bought a 95Z28 from this board back in 2008, engine had been rebuilt with forged pistons, blower cam, etc., and an S trim supercharger. From what I remember the engine was burning coolant, taken to a shop that removed the heads and said the head gaskets were ok. Engine was reassembled and I bought it as is.
Just took it out of storage since 2008 to finally work on it. Couldnt remember the specifics of the problem, engine ran fine but the radiator was dry so I filled it with water to run the car and see what the problem was. Car did not make the white fog I was expecting, ran fine, and then I checked the oil and found a lot of the water was going in the oil. Shut down the car and pulled the engine.
Drained the oil and water mix and started taking the engine apart. I expected the milkshake of oil and water everywhere but did not expect this when I pulled the right side cylinder head.



Head gaskets were fine, looked new, so I assume they were replaced when the heads were originally pulled. Combustion chambers do not look steam cleaned.



Did see this "spot" in the suspect cylinder.



So now I have water in the crank case and in the cylinder as well.

Took the heads to a machine shop to be pressure tested and checked for flatness, all checked out, no cracks and flat to .002" or better. So heads are ok, head gaskets were ok.

No obvious cracks in the block, but next is to get it pressure tested as well. I assume it is cracked, but shouldnt I be able to see a crack large enough to put a gallon of water in the pan in a matter of minutes? Also the engine was not making white smoke and ran fine, so the coolant in the cylinder must have seeped in while the engine was sitting after being pulled.

Anyone ever crack a block like this?

 

Has the block been bored? Is so, how much?

Many.... (very) many years ago, I bought a 283 SBC short block cheap, and found a small pinhole in a cylinder wall. Had been seriously overbored, walls were paper thin, and must have exposed a small imperfection in the casting. Never ran it, never filled it with coolant, so never experienced exactly what you did.

 

Pistons arent marked, but supposed to be .030 over, havent confirmed it yet. What is strange is how fast it got water in the pan, did it very quickly. Confirmed the oil cooler was not the problem, oil was not getting in the coolant, just the other way around. Did it with the radiator cap off while the engine was running, so the coolant was not even under pressure.

 

Was there any evidence of thread sealant on the studs and bolts? I wonder if they assembled it with new gaskets and such.

I'm not sure what the flatness spec is on LT1 heads, but I can tell you that I was leaking coolant with them just 0.003" out. Nothing like above, but it was cooling funny and it was very clear on the head gasket that the coolant was moving between passages(overheated the engine...260*+...temp gauge was pegged...).

Both 6 and 8 look really clean compared to 4 in your first picture. Do you have shot of the other side with the head freshly pulled and untouched?

 

[QUOTE=ACE1252;6967013]Was there any evidence of thread sealant on the studs and bolts? I wonder if they assembled it with new gaskets and such. QUOTE]

from this side of the internet I see in OP's pic evidence of thread sealer on the block head bolt holes....except the one in the upper right.

with that much water/coolant in a cyl and the motor ran..and didn't hydro lock...wow

 

I doubt the block is cracked to be honest. Looks like the cylinder head may be suspect though.

 

Maybe a crack inside the head leaking into a intake or exhaust runner? Lucky you didn't hydro-lock that motor!

 

....

 

The late model block cracks that I have seen are in the lifter valley below the head bolt boss, it's actually quite common with the late light duty castings.










Somebody missed the crack on that guy's rebuilt motor, so I just fixed the crack and put it all back together.

....


Finding milkshake in the pan, plus tons of water in the cylinder doesn't sound like a valley crack though, I would imagine that cylinder is either cracked, or a sleeve was installed improperly after a previous failure.

 

Just curious ... I am no machinist by any means ... but I am pretty well versed in wrenching on cars, diesels, etc.

Why is it repaired in that manner?

Rather than just grinding it down, and filling with weld?

I assume it is somehow to get a much stronger repair but I am blanking at the moment. You can PM me if you prefer rather than derailing his thread.


Injuneer - I guess I should have clarified what I meant, a crack in an area that maybe was overseen inside a port or something. But I guess a good shop checks over a head with a fine tooth comb when it is suspected as problematic.

 

I still have to get the block pressure tested, but I suspect the water in the cylinder may have come in around that hot spot while the engine was sitting idle and not running, maybe a pin hole there? There was little to no steam coming out the exhaust so not much was pumping in there while running.
The tough part is figuring how the water got in the pan so quickly. Block will be pressure tested soon, been working on the vehicle that the engine is going in. The machinist is as curious as me on the source and wants to check the block.

 

You may have missed this comment. Is there any evidence that the block has been sleeved?

 

Honestly I have never seen a sleeved block, is it visible from the top or only from the underside? I assume I would see the machined step in the block from the bottom.
I was not told that it had been sleeved but I will have to take a closer look at the block.

 

To weld cast iron properly you have to put a ton of heat into the metal around where you're welding, and if you do this without heating up the whole casting you will end up with even more cracks. It's not as simple as hitting it quickly with a MIG gun, that doesn't stick to cast iron, you have to do a oxy/acty torch spray weld or TIG weld with nickel rod...both processes put a lot of localized heat into the metal.

Once you heat up the block like this it distorts quite a bit and needs to have most of the machined surfaces touched up and round holes fixed. So risk of more cracks, distortion of the casting, and how quickly you can do a tapered pin repair are why it's chosen for some repairs over welding.



If it's put in properly and machined well afterwards you would have to look pretty hard to know that it's there. There will be a very fine line around the bore where the separation between the sleeve and the block. With small blocks we use a 3/32" wall sleeve which 90% of the time isn't thick enough to require boring out into water so usually the sleeves have no chance of leaking.

 

Unless the materials are noticeably different most people can't tell a sleeved block from a non-sleeved block, especially if the block is dirty.

When I say noticeably different I mean like aluminum blocks with iron cylinder sleeves or liners. Look up a sleeved LS1 block for reference.