thats a very odd sequence of events.....
Carnage........Whats your take?
- Thread starter jdpolzin
- Start date
maybe a stock crank will last, maybe it won't.....the point is that a steel crank will last. most of the broken cranks ive seen have been in 11 sec cars. how were the headgaskets in Austins 4.1?
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- Feb 18, 2006
I agree. Not real sure about that analysis. I don't think ivevever heard of a block blowing out the cylinder because of cylinder pressure?
turbonut85
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- Apr 11, 2008
There is really no way of knowing for certain what sequence of events actually took place...that was the first thing that was made clear. Obviously the crank broke, and that caused the majority of the damage...no question. There was very minimal fretting on one of the main caps....so detonation was present....no question. I'm not sure I completely agree with the hydro locking theory myself...but the way they were analizing and pointing things out to one another, it seemed to make sense...I'm no expert so I can't confirm nor deny what they think happened. The way the crank broke, there was a serious down force at the rear, on #5&6...every main cradle was broken in the block. There isn't a single cam bearing that has block material surrounding it...in fact, the rear cam bearing was scooped up by the crank counterbalancer! All the bearing surfaces looked as perfect as they could be...(except where the crank flattened some edges) The #6 cylinder wall is pushed out about 3/4 of the way toward the top. I will try to get more detailed pics tonight.
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turbonut85
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- Apr 11, 2008
turbonut85
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- Apr 11, 2008
The shiny spots and the lines in the casting where the crank snapped are what raise questions in my mind...it had to have rotated a few times after it cracked...but at 5000 rpm it doesn't take long to rotate a few times...lol. Idk??
austinibew145
Well-Known Member
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- Apr 7, 2008
We looked at the head gaskets. They were cometic gaskets. They didn't show signs of stress.
The last picture there tells the tale to me. That looks like a crack surface on the crank which started at the fillet or oil hole and worked its way out. That nice flat surface is where the crack grew, the mashed up area on the outside indicates plastic deformation from where the remainder of the section failed under load. This was the initial failure, the rest of the damage happened after the crank became two pieces.
It's similar to another crank that I had crack about 10 years ago that was in a ford escort that was stock and never abused. In fact the engine ran fine, I only found the crank was in two pieces when investigating the small knock it created. By the way, for those who say “we’ll never know what happened”, people can use microscopy to get a good idea of how long that crack was growing... so there is a way to be more certain if you really wanted to. To the untrained eye though it looks like that crack was some time in the making because of how smooth and flat the surface is, similar to my escort crank.
As the crack grows and the section gets smaller, stress will increase at similar loads, this explains the mashed up material at the outside (LHS of the picture) of the crack. If there was failure after "hydrolock", then that surface would not look smooth like it does. If the harmonic balancer was the problem (this is even less plausible to me), it would have cracked a journal closer to where the balancer was.
People are right when they say that these cranks have a life. Every cycle they accumulate some amount of damage, the higher the stress the more damage. Even a perfect crank at low stress levels will eventually fail. Throw in a casting flaw (my escort) or higher stresses, and the life will decrease dramatically. No doubt that cast may last a long time, especially at lower stress levels, but under similar conditions, forged steel has a much higher life. Each person should consider this when choosing a crank.
It's similar to another crank that I had crack about 10 years ago that was in a ford escort that was stock and never abused. In fact the engine ran fine, I only found the crank was in two pieces when investigating the small knock it created. By the way, for those who say “we’ll never know what happened”, people can use microscopy to get a good idea of how long that crack was growing... so there is a way to be more certain if you really wanted to. To the untrained eye though it looks like that crack was some time in the making because of how smooth and flat the surface is, similar to my escort crank.
As the crack grows and the section gets smaller, stress will increase at similar loads, this explains the mashed up material at the outside (LHS of the picture) of the crack. If there was failure after "hydrolock", then that surface would not look smooth like it does. If the harmonic balancer was the problem (this is even less plausible to me), it would have cracked a journal closer to where the balancer was.
People are right when they say that these cranks have a life. Every cycle they accumulate some amount of damage, the higher the stress the more damage. Even a perfect crank at low stress levels will eventually fail. Throw in a casting flaw (my escort) or higher stresses, and the life will decrease dramatically. No doubt that cast may last a long time, especially at lower stress levels, but under similar conditions, forged steel has a much higher life. Each person should consider this when choosing a crank.
dr_frankenstein
Mad Scientist
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- Mar 17, 2008
Very Interesting Diagnosis..........
I don't buy the hydrolock idea. If the cyl wall cracked, you'd pressurize the radiator, not suck in water, certainly not enough to blow the engine apart.
Think if it this way, how many head gaskets have blown to the cooling jacket (think milkshaked oil) ? How many of them hydrolocked?
I have seen the long-growing crack issue on axles before, and the signs are easy enough to see. (afterwards....)
Bob
Think if it this way, how many head gaskets have blown to the cooling jacket (think milkshaked oil) ? How many of them hydrolocked?
I have seen the long-growing crack issue on axles before, and the signs are easy enough to see. (afterwards....)
Bob
turbonut85
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- Apr 11, 2008
Crank was "dry magged".
turbonut85
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- Apr 11, 2008
Theoretically, if the hg blows, it's at the top of the bore and the coolant has a place to escape the combustion chamber...(milk shaked oil etc)..but in this case, hypothetically, since the cyl wall is cracked below the top of the bore about 1-1/2" down ( pushed out from the inside)....and the glued cometics were still intact, the piston, on its way down, sucks some coolant into the bore, but on the way back up, with both valves closed(compression stroke) the coolant has no where to go, and will not compress....there only had to be enough in there to fill the piston dish and the 45cc head chamber...is it possible?? Thoughts?
Did these machinists explain why the hole in the cylinder opened up 1.5" down the cylinder? Why not toward the top of the cylinder where the pressures are much higher? If excessive cylinder pressures were the cause, why did the cylinder fail instead of a head gasket, piston or crank which all seem to be weaker leaks in these engines?
People on this site with a lot more knowledge than I might be capable of anserwing this question much better than I can, but I am not sure at high rpm there is enough time for enough water to leak in (coolant is about 10-15 psi), overcoming both boost (you were over 20 psi boost right?) and cylinder pressures to hydrolock the mill. Hydrolock would be worse at lower speeds bc there is more time and less pressure for water to leake in I believe.
Maybe someone can show us a P-V diagram for one of these engines at your boost level and see if your cylinder pressures are < coolant pressures on the intake stroke 1.5" from TDC. If they are then hydrolock is possible but if not....
People on this site with a lot more knowledge than I might be capable of anserwing this question much better than I can, but I am not sure at high rpm there is enough time for enough water to leak in (coolant is about 10-15 psi), overcoming both boost (you were over 20 psi boost right?) and cylinder pressures to hydrolock the mill. Hydrolock would be worse at lower speeds bc there is more time and less pressure for water to leake in I believe.
Maybe someone can show us a P-V diagram for one of these engines at your boost level and see if your cylinder pressures are < coolant pressures on the intake stroke 1.5" from TDC. If they are then hydrolock is possible but if not....
Where is the "hole" in the cylinder? If that's it I see in the fourth picture on this page, its not from the cylinder being over-pressurized, but rather some part punching it out. A failed cylinder would not have a clean area punched out, but deform and eventually crack along the long axis of the cylinder bc the hoop stress is more than 2x that of the axial stress. I have attached a picture of what would be more expected. I did a quick google search for over-pressurized cylinders and they were all similar to this, none had an almost perfect hole punched out.
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fastblackracing
Well-Known Member
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- Apr 7, 2009
Bryesh, I think you have some good input here, to add what I know about cooling systems-- I have measured pressures of up to 60 psig, in the intake crossover passage at elevated rpm above 4000. This would be the pressurized water pushing against the t-stat and include the block,heads and intake seeing higher pump pressure and the pressure after the t-stat drops going into the radiator and eventually back into the pump inlet which would be the lowest pressure. Yes you can have 60# of pressure with a 15# cap. The pressure varies thru the whole system. This still looks like a broken crank to me, sometimes they take out everything else and sometimes not.
So, this leads to my next question. Could this crank and balancer break due to a poorly balanced rotating assembly? The bearings look good but I would think a bad balance would eventually cause a crack, not necessarily damaging bearing/journal surfaces. Possibly cause a crack in the block above the caps?
