OK, I'll ask. Has anyone found a defect in that area? For that matter what, if any defects were found on any cranks and where?
Cranks
- Thread starter Fingers
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The only defect I found was the one I posted on page one... It is very small & can't be seen with the naked eye. Since this thread & discussion has started I have since changed my opinion on the failures, from flaws to a harmonics issue.
I'm not an engineer... So I appreciate Fingers & some others taking the time to put there thoughts in "layman terms" so us stupid folk can follow along
I'm not an engineer... So I appreciate Fingers & some others taking the time to put there thoughts in "layman terms" so us stupid folk can follow along
Can't get you guys off the manufacturing defect idea, can I.
Some cranks bust at stock HP in under a year. Others last 500,000 miles.
While harmonics are probably a major stress load on the crank, there are cranks that don't ever break.
I see what you're implying. However, this could also be explained by variability in assembly. A thousandth here, a lb/ft of torque there, added all up and no two engines probably run exactly the same. Hell, I have an LBZ that dynoed "weak" at 285 stock on a considered accurate machine. Something's got to explain stuff like that; I lean to variability in components and assembly.
In other words, some engines might leave Morraine, OH with a rubber band as a part of the package...
In other words, some engines might leave Morraine, OH with a rubber band as a part of the package...
like I said I drove my zf6 truck with a bad dual mass flywheel for a few weeks and it would straight rattle your teeth out. smoothed out at highway speeds but at idle it was crazy shakey. and with all those harmonics going on it is holding on so far. that was thousands of miles ago. so maybe it is a harmonic issue but it magnifies on certain trucks for some reason. guess its just that "some reason" we are after. mines an 01 so I would think it would have the most crank flaws but I could be wrong they could have changed processes since then. its just crazy the breaks are so random there is no control to be found on all of the trucks exept they are all dmaxes lol
This may have been mentioned but the old 6.2's broke cranks and they were only at around 160 cshp.
my buddy broke a 6.2 crank cruising at 60 mph the day he got it legal. but I had a 6.2 that the harmonic balancer was bad the whole year I drove it. made a terrible knock, finally figured out what it was when it broke the side of the keyslot for the keyway for the harmonic balancer off the end of the crank letting it slip. lost all acsesories. took a while but the harmonics caught up to it.
6.2 crank failures
6.2 failures were demonstrated to be a harmonics issue, and the most frequent cause on inspecting the carnage almost every time was found to be a worn/completely failed elastomeric harmonic dampener. I grabbed a military surplus one and sure enough one of the accessories that had been changed out during its military life was the harmonic dampener and crank pulley. So far I've been lucky with that crank.
It's a documented fact that crank breakages affect every model duramax at any power level, and I'm assuming the equipment on the assembly line and their crank forging process has evolved slightly over the years. Given that the overwhelming majority of failures are at the first throw, the most likely cause would be harmonics focused in that area. (Unless you want to believe GM has manufacturing flaws that always occur in the first throw and somehow have never been fixed through multiple evolutions of the dmax) Sure a manufacturing flaw at the wrong spot could exacerbate an existing harmonic issue and make failure much quicker, but I have a hard time believing the first throw is that much MORE likely than the rest of the crank to have a manufacturing flaw.
I understand none of us wants to believe there is a critical design flaw in our trucks and its always easier to make it into a manufacturing fluke, but we should probably give up pushing the manufacturing flaw theory and let the man "think out loud".
6.2 failures were demonstrated to be a harmonics issue, and the most frequent cause on inspecting the carnage almost every time was found to be a worn/completely failed elastomeric harmonic dampener. I grabbed a military surplus one and sure enough one of the accessories that had been changed out during its military life was the harmonic dampener and crank pulley. So far I've been lucky with that crank.
It's a documented fact that crank breakages affect every model duramax at any power level, and I'm assuming the equipment on the assembly line and their crank forging process has evolved slightly over the years. Given that the overwhelming majority of failures are at the first throw, the most likely cause would be harmonics focused in that area. (Unless you want to believe GM has manufacturing flaws that always occur in the first throw and somehow have never been fixed through multiple evolutions of the dmax) Sure a manufacturing flaw at the wrong spot could exacerbate an existing harmonic issue and make failure much quicker, but I have a hard time believing the first throw is that much MORE likely than the rest of the crank to have a manufacturing flaw.
I understand none of us wants to believe there is a critical design flaw in our trucks and its always easier to make it into a manufacturing fluke, but we should probably give up pushing the manufacturing flaw theory and let the man "think out loud".
Older detroits
Older detroit 53 series were also known for crapping out cranks in certain cylinder arrangements when people cranked them up with some 71 series injectors, etc. Even the few modern day nuts who try to hot rod the 53 series seem to snap a crank before anything else lets go, assuming it doesn't run away on oil from the blower or start up backwards or any other madness those things are known for.
Those were the days before elastomerics.
Older detroit 53 series were also known for crapping out cranks in certain cylinder arrangements when people cranked them up with some 71 series injectors, etc. Even the few modern day nuts who try to hot rod the 53 series seem to snap a crank before anything else lets go, assuming it doesn't run away on oil from the blower or start up backwards or any other madness those things are known for.
Those were the days before elastomerics.
The main problem seems to lay with the firing order, we have seen billet cranks break, so a problematic quality control or manufacturer defect is not likely. So that leaves the design weakness or harmonics you have been talking about. Jon can you stimulate the harmonics between the stock and new firing order to see if the crank problem lays in the firing order?
Modeling the harmonics is where his static FEA software is pretty near worthless, and that's really probably why he hasn't posted a way to prove these theories yet. With no simulations, the only other option is experimental data but how best to measure harmonic variations between a factory firing truck and an alternate firing truck, or a stock harmonic dampener and a fluidampr is the problem.
Right now were sitting at a point of suspecting its a harmonic problem, but having to way of proving it through models or testing, and also no method of proving a better alternative. Stories of "this crank broke and then we found this defect" or " my uncles pulling truck is XXXXhp and hasn't broken and he has an alternate cam" are great, but from looking over fingers' posts he's obviously a man of science and circumstantial evidence doesn't prove anything.
Really what needs to happen is a solid scientific harmonic testing/measuring idea, or somebody with serious modeling software needs to cough up that licensing info or develop an accurate model.
Right now were sitting at a point of suspecting its a harmonic problem, but having to way of proving it through models or testing, and also no method of proving a better alternative. Stories of "this crank broke and then we found this defect" or " my uncles pulling truck is XXXXhp and hasn't broken and he has an alternate cam" are great, but from looking over fingers' posts he's obviously a man of science and circumstantial evidence doesn't prove anything.
Really what needs to happen is a solid scientific harmonic testing/measuring idea, or somebody with serious modeling software needs to cough up that licensing info or develop an accurate model.
We've got plenty of engineers, the will to prove and solve a problem, and a hypothesis on what's wrong and a fix.
We don't have an accurate enough dynamic model to prove anything mathematically and we don't have an experimental design that'll give the data we need.
We don't have an accurate enough dynamic model to prove anything mathematically and we don't have an experimental design that'll give the data we need.
I've been able to pull some initial info from looking at and comparing the pulses from the converter speed sensor and the crank position sensor on a scope. Wish they had the same pulse per rev count. It would make the phase shift easier to see.
The software I used for the chamber pressure monitor system has a decent crank signal visualizer. I think I can overlay the converter signal over the crank signal graphically. That should show flex. Actually, I was thinking the converter signal should be the baseline and the crank signal superimposed on that. I expect the converter signal to be more phase stable considering it's larger inertia.
I should have an accuracy of about +/-0.25° at 3000 RPM and better at lesser speeds.
The old software already has a record function, so I should be able to save the raw data.
The software I used for the chamber pressure monitor system has a decent crank signal visualizer. I think I can overlay the converter signal over the crank signal graphically. That should show flex. Actually, I was thinking the converter signal should be the baseline and the crank signal superimposed on that. I expect the converter signal to be more phase stable considering it's larger inertia.
I should have an accuracy of about +/-0.25° at 3000 RPM and better at lesser speeds.
The old software already has a record function, so I should be able to save the raw data.
So that shows any RPM and condition where the torsional strain increases or oscillates over the entire crank right? And we'd have to assume that the harmonic effect is worst at the first throw sincewe can't isolate torsional strain any more precisely. I'm assuming the crank signal is up front...
Is it your truck? Is the aftermarket dampener going to skew results, or have enough super damper equipped trucks snapped cranks to assume its a wash?
Is it your truck? Is the aftermarket dampener going to skew results, or have enough super damper equipped trucks snapped cranks to assume its a wash?
No, it will show the relative position of the flywheel end vs the pulley end. That is, the twist in the crank through the rotation. (actually two rotations) We will track RPM, as a numerical value for each frame.
If I get it working for my truck, we can hook it up to most any truck and start collecting data on engine variants.
I suspect we will be able to bracket the range of the base harmonic from the data.
If I get it working for my truck, we can hook it up to most any truck and start collecting data on engine variants.
I suspect we will be able to bracket the range of the base harmonic from the data.
That's definitely as good a plan as any, especially if you really get the accuracy you mentioned earlier. How quickly do the sensor outputs update with your monitoring system? Will you have anything close to a smooth curve of continuous analog output, or connect the dots 20 times a second? If its a slower refresh, do they update at the same time, or are they offset by a set amount in the Rotation? Sorry if it seems like I'm poking holes without offering a suggestion here, just wondering what you're up to.
I haven't read up on your cylinder pressure system yet, but I'll definitely look for it now. Is that why your dyno numbers look like some torque is tuned out? Optimized cylinder pressure through tuning? I'd imagine you've got it responding smoother than stock with doubled injector flow and 690 at the wheels. I always see everyone pushing 40% overs or whatever on crazy pulses and 700+hp and it never seems like a good idea to me.
But I've never changed common rail injectors so what do I know...
I haven't read up on your cylinder pressure system yet, but I'll definitely look for it now. Is that why your dyno numbers look like some torque is tuned out? Optimized cylinder pressure through tuning? I'd imagine you've got it responding smoother than stock with doubled injector flow and 690 at the wheels. I always see everyone pushing 40% overs or whatever on crazy pulses and 700+hp and it never seems like a good idea to me.
But I've never changed common rail injectors so what do I know...
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