Long story short for those unaware, last year I had a problem with combustion gas in my coolant so I tore down the engine. I had the block pressure tested ... all was good. The deck surface was checked and it wasn't straight, so 0.008" was taken off. The assumption by the engine builder was the combustion gas being in the coolant could have been caused by the deck not being straight. (Side note: the work I just described was performed by two different engine builders ... there was a reason, it obviously muddies the water, and I can get into that if need be.) Below is a link to the thread if anyone would like to get more details on the coolant issue: https://www.v8buick.com/index.php?threads/coolant-system-pressurized-when-cold.380774/ As part of the block work, it's was align honed, oil mods were done, the decks were trued up, the cylinders were honed with a torque block, cam bearings installed, and the block was hot tanked. Once I picked up the engine it sat for a few weeks until I had a chance to start working on it. Yesterday I thoroughly washed the block and oiled it down. Today I uncovered the block to test fit the rear main seal and I found what seems to be a crack in the wall of cylinder #2 ... and it happens to be right in front of a coolant passage. Below are some pictures. There are two dark marks. The one further in the hole actually looks like an indentation. The one closer to the top appears to have a crack running up and down in the cylinder. I'm guessing the next step is to die pen. the cylinder.
What’s the current bore of the block? And did you have it sonic checked? You may be able to sleeve the block.
The bore is 4.35" (0.038" over) and the block was not sonic checked. I requested it, but the engine builder said it wasn't necessary. Do you have any idea how much a sleeve would cost? The theory that was presented in the thread I referenced above was the crack was tight enough to prevent coolant (at say 25 psi) to pass into the cylinder but wide enough to allow combustion gas (at say 1500 psi) to pass into the coolant. So a pressure test, even at 100 psi, may not be enough to show the crack. Another factor is the crack may only be an issue when the engine is hot, which can't be simulated during a pressure test. I'm wondering if the honing and hot tanking could have made the crack more apparent.
My machinist buddy talks about this now 'n' then. Bore a block...looks perfect. Come back the next morning, and there's one or more dark spots in the cylinder wall. He thinks it's slag inclusions in the iron. Says he sees it most often in Ford small blocks--slack foundry work. You may have to sleeve that hole. No big deal, except for the extra time wasted, and the cost of the procedure.
I'm guessing you should take it to the best machine shop you can and see what they say. If it is cracked, I'd say a sleeve is your best option to salvage the work you've already invested in. It will probably be at least a few $100 but in the grand scheme of things, it will be solid.
In my mind it seems unlikely based on the position and angle of the "crack" that it would continue through to the coolant passage? That of course is a guess. There is no way to tell without some kind high tech analysis. I would look at sleeving it...
Liquid penetrant, and Magnetic Penetrant Inspection (proper level) NDI (Non-Destructive Inspection) is needed. It is not cost prohibitive, and if the machine shop has the capability to do the inspection correctly. Then you can know if you have a crack and then you can determine if a sleeve is a cost effective fix. Don't leave it to guessing, or "what iffing" yourself into a dark hole. (no pun intended). Get it sorted, then weigh and decide. It's hot, racing sux right now.
I had a block the developed a tiny pinhole....it was about halfway down.....we never got games in the coolant but we would get coolant in the oil......if I ran with no cap on the cooling system it stopped the coolant in the oil. You can also get games in the coolant from a bad head gasket and cracked head
Given how high up what looks like a crack is in the bore.....alot of blocks are solid up there. The coolant passages around the cylinder is lower. But you can see the hone stone never touched those 2 areas. They are just a area that is lower.....going another .01 might clear all of that up. I've seen low spot like that several times. I have a 454 block it was standard bore.....went .030 over and it still has a few eyebrows that the bore and hone didn't touch.
My 350 has a glob of iron that looks like those dark spots in #1 been like that for years. Machine shop said ‘bout the same thing Schurkey said, random hunk of slag or something.
I reached out to the engine builder who machined the block and shared the pictures in post #1 with him. He said he vaguely recalls seeing the two spots in question and didn't recall having any concerns with them. One reason is because he pressure tested the block and it checked out. He offered to take another look at it. Since he's not local I decided to take the block to a engine builder near me just for a second opinion. He was able to tell it was a crack just by looking at it, but was surprised by its location. Below is another, hopefully better picture of the crack: I asked him what he would do. He said it was a tough call. He brought up sleeving it, but said he was leaning towards running the engine as is based on the location of the crack, the block pressure tested okay, and sleeving doesn't guarantee the depth of the crack will be removed (i.e., the crack may still cause a problem in the future). Here are my thoughts ... The "crack" did not initial as a result of stress, but rather from an inclusion or void during casting. I'm assuming this because of its shape (it looks more like a void to me than a crack that has opened up) and its location (high in the cylinder, so not subjected to sideloading from the piston ... it only sees forces from the combustion of fuel). However, since a discontinuity does exist in the cylinder wall there is a concern that it could propagate over time. Soooo, I'm leaning towards sleeving the cylinder, but I'm wondering if there are any down sides to sleeving (other than cost and time). For example: Can sleeving somehow make the situation worse since the cylinder has to be bored a significant amount to install the sleeve? (e.g., Will it weaken the adjacent water jacket, because of how much material will be removed, and possibly lead to a crack and coolant getting in the oil in the future; or are there concerns with the remaining cylinder wall being strong enough to support the sleeve without cracking in the future, since these cylinder walls are fairly thin from the factoring.) My understanding is the block will need to be decked again to make the sleeve flush. The way the block sits today, my pistons will be 0.003" out of the hole, I was going to use a 0.041" head gasket, which equates to a 0.038" quench. More decking means the pistons will be further out of the hole and I'll have to use a thicker head gasket. Is this a concern? Thanks, Jim
