Hello again. Got the heads off for a gasket change/stud job, and was inspecting the cylinders/pistons. Saw this in the second from the front on the drivers side (4?) and my heart sank.




Sorry for the large pictures, but I wanted to show as much detail as possible. I strongly fear it's a crack, although that's not something I've read about happening with stock or tuned only 6.0's before. I can't feel it with a fingernail, and there were no symptoms. Truck started easy, ran fine, crank was nice and even, did the coolant pressure test at full throttle up a good grade and had no spikes. No coolant/oil mixing.

I don't know that it's an incredible amount better, but I'm hoping it's a score/scratch from a foreign object. If you saw my previous thread regarding my turbo, it's a real possibility that something went through. There is also that impression on the piston, which unless some pistons came with such a defect, would also indicate a foreign object. I don't know if there is a cylinder liner on a 6.0, but assumed it was all cast as a unit and machined. I notice the mark terminates immediately at the top of the pistons travel, which would seem to indicate an object being pushed by the piston. That is unless the deck and cylinder liner are two separate pieces, and the crack simply terminated at the junction.

On the other hand, I'd moreso expect a score mark to be straight, not crooked/jagged. Otherwise, this would mean the object had to be moving around the edge of the piston as it was being pushed. Here are some more pictures to help you look. Sorry for the long post. I'd greatly appreciate responses from anyone, but would particularly love them from someone who has rebuilt one before or ideally, works on them as a day job.

 

Well, that's a tough one.. As someone who worked in an automotive machine shop for a couple of years a long time ago I can make a couple of observations. Firstly you are correct that score marks are almost always a straight line and cracks seldom are but if it happened at low speed like during cranking or turning the engine over by hand it could be a score. Secondly, no loss of coolant or signs of coolant in the cylinder is a good sign but not enough to trust it for reassembly. Is that a small piece of metal peeking out between the cylinder wall and piston? Ther also appears to be a small drip of slag on top of the piston that has carbon covering it. May be some insight into when the damage happened.

In the end, you need to KNOW what it is before investing the time and money for reassembly. Luckily that is possible. I'm not sure if you can talk a local machine shop into coming to you (or how much it might cost) but the tools to magniflux it are portable enough to do that, or possibly you could trailer the truck to them. Eddy current testing would be even better and is also portable. Unfortunately dye penetrant isn't practical in this situation unless they have some new equiptment I don't know about.

 

Would agree Rusty, as someone who also spent some time in the machining side of things I can't say I ever saw a crack that had the straighter appearance shown in those pics, without fail always a degree of jaggedness to it. From what I remember as well cracks tended to have a darker appearance, not the scuffing as shown here.
I guess at the end of the day it's your truck and your call, but from what I have seen from my five years stint that included a lot of time running a black light, I know what I would do if it was mine...........bolt her back together.

 

It does have an appearance of a crack rather then score, but it doesn't propagate to the non ring contact area.

Maybe it's the way these tired eyes are seeing, but was that cylinder sleeved? Some of the lines in a few photos gives me that impression.

 

Do any of the other pistons have that mark.. looks like an arrow to me? Maybe so all the pistons are faced the right direction or for ring alignment?

That score stops right at the top of travel and a second, slightly less prominent, matching mark is parallel to the deeper score. That would indicate that whatever it was, was at an angle, like it was pinched and exerted more force to one side of the object as it was pushed to the top.

I don't work on rebuilding truck motors daily, but rebuild outdoor power equipment and see plenty of piston and cylinder carnage, in the thousands. Cylinder walls can withstand some serious abuse, pistons cannot. If that were a crack, I'd think it would occur in a location near the next cylinder where it's thinner or near a bolt hole AND that you should possibly see a corresponding crack on the other side... cracks are caused by flexing.

I don't think the crack would have stopped at the top of the stroke, especially since the edge was only a very short distance away and that would have to say that the crack only cracked in the middle... like a bulge. Which doesn't make any sense... at least not to me, a bulge would have effected the cylinder next to it potentially.

The honing marks are still perfectly aligned. Score marks are almost always straight...but the foreign object rode the piston for some time causing them to be straight. If this went up once and out... then it wouldn't have worn a groove.
Does it catch a small pointed object, say the tip of a pick type tool?
The marks heavy at the top, much lighter at the bottom.

I'm with the guys above... bolt her up and go.

 

I greatly appreciate all the valuable input. I didn't notice that lighter mark paralleling the main before, so that's a great catch. Seems to further indicate it's a score. I got the smallest tool I have, a pic, and gently pulled it across the mark. I couldn't feel it catching. Here's a picture of it:




Went by the machine shop to see what I could work out there, but they were already closed. Feeling quite a bit more optimistic though. Thanks again.

 

I too was doing gaskets and studs and found this...#7 cyl

 

I feel for ya. That's a sucky discovery. Was the engine giving symptoms of a cracked piston? Was the motor tuned?

 

No symptoms and had just bought an X4 and had loaded one of the canned tunes. Initially when I bought the X4 I had nothing but problems with it connecting, had to send it in for warranty, SCT was aware of the problem with it (seems they had some produced that had syncing issues and I got 1). Finally got it back from them with new internals and everything seemed fine. Was running 1 of the canned tunes for about 2 weeks (don't remember which) and went out to start it one morning and about 30 or so seconds into it idling there was a "miss" and it felt like someone hit the block with a 12lb. sledge hammer. It ran like normal but after a few days I went back to my X3 with custom tunes by Matt.
Months later while doing my weekly fluid checks I noticed oil in the degas bottle, ran some tests and narrowed it to failed oil cooler. I was already prepared with slowly buying studs, head gaskets, BP EGR cooler, etc. So when the heads were pulled (after lifting the cab) we found the cracked piston and had to now pull the block. New pistons, rings, etc. and it's back up and running. I gave the X4 to my dad to use for it's monitoring capabilities and told him not to load any tunes from it. I do not know 100% that it was the X4 tune but pretty sure of it. The shop that did the work (I don't have a lift otherwise I would have done it myself) said this was only the 3rd one out of 1000 that he has seen a cracked piston...1 was on a completely stock, never tuned and 1 was over tuned.