4a block strength

[rms]

Some study of thermodynamics and metallurgy may help correct some misconceptions.

[jeffro ra28]

Without seeing the specimen in mind, its hard to make a conclussion.

you could elaborate to me via PM about your thermodynamic and metallurgy study if you wish to continue this discussion

[allencr]

I'd go with rms on this one.
While I've got zero experience with boosted engines and their ability to self-destruct very quickly, I think I do know that
a. cylinders don't split without just cause --- it's bored out way to much or detonation.
b. pistons & rings don't melt from water, especially from a small dribble that would only have at most 1/1000th of the pressure used in water cutting equipment 30-80,000PSI(and no abrasives either!) -- it's detonation.
c. valves are destroyed by heat and water jackets are cracked by heat -- it's a burnt valve.

It's cause then effect, not effect -> cause.

http://en.wikipedia.org/wiki/Water_jet_cutter

[oldcorollas]

just to add my 2c
i think many people jump to conclusions about the origin, mechanism, and cause of engine failures. unfortunately, the conditions inside cylinders cannot be easily reproduced in lab (at least in my lab )

typically it is limited to things like "it ran lean, and burnt a valve" or "it detonated and burnt a piston" etc

[3sgte]

At the risk of throwing fuel on the fire, I also am going to go against the water thing.

That piston has been melted by combustion pressure leakage. Just as leaking combustion pressure will cut an exhaust valve, the leaking pressure here has cut the piston.

As RMS mentioned, detonation (that results in a broken ring or land) will have the same result on a piston.

Look at the ends of the rings, they are bent down because that is the direction the flaming hot gasses leaked.

Next question is chicken or egg.
Did the rings/piston leak in this area because the bore split? (this is my guess)
Did the bore split here because the ring or land broke causing the combustion leak?

Please note, I have no idea if detonation played a role in the bore splitting.

Based on the pic that 30psi 4agte posted, it looks like his bore split first. In his case, the bore split all the way up to the headgasket, where the combustion pressure leaked before it had a chance to cut through the piston.

[jeffro ra28]

Fair point guys.
First off, the crack occurs in this place very commonly, right next to head stud, so it was not a broken ring that caused the crack.

Now another possibility which is what i first thought when i took the head off was that when it cracked, it shifted the bore, changing its shape around the top of the cyliner. One side of the crack would have been feircly rubbing on the piston top lands and rings because it had deformed the bore imediately at this point, creating a shit load of friction =heat.
Which i have tried to explain in the photo bellow. This is what i mean by "shifted".
The outside coloured in black area on the top veiw represents the shifted section. The red line represents the new shifted bore outline. Imediately at this black coloured in section from top veiw is where the piston was melted away.



Which may have been the initial cause of the cutaway/melting. But then when i removed the piston from the engine and had a look down the side, which is when i came to the water cutting conclusion, only because of the type of finish it left on the side of the piston. Which as i explained as "cutting finish". Perhaps this occured last in the process, and gave it this affect.

I guess until we can monitor this process in real time, no-one will really know.

Still my conclusion is still that a split bore caused the piston to melt away, whether it be the friction created due to shifted bore at this area, or the water, or both combined. In my mind it definantly was not detonation.

[fixeruperer]

whoops here's a bit of a blow up all the pistons were nackerd but this one takes the cake. choose your tuner wizely.
This engine had JUN sleeve's in it but the piston caught it and it need's a bore.