Broken Crankshaft Count?
- Thread starter EDP
- Start date
Which would make sense because at low rpm with not much boost the imbalance without air being crammed into the cylinders would be far greater. I'm sure some brakes are due to other broken parts but the majority I'm starting to believe the imbalance theory. Nothing else really holds true and the fact that the AF cam helps points directly at that being the case.
I wonder if moving the intake inlets to center would help at all? Be easier for most than a cam swap. Aim them into the valley and forward then up.......
I think it is more the clam shell style intake and what is needed is a manifold with individual runners like Wagler's new one.
Maybe it is air related but the stock Cummins intake is more inefficient and off balance than the Duramax clamshells. They don't break cranks. 7.3 powerstrokes also have a similar intake manifold setup.
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Can't compare it to a Cummins couldn't be a more different platform... I have no knowledge about the Ford. The intake balance problem is a shot in the dark as well but seems to make sense. The way I see it, it has got to be some sort of a harmonics problem. The fashion in which they break doesn't point at a weak crank as they are breaking where torque application should be the least and from what people are saying not breaking under power.
Could be a combo of both harmonics which turn the crank into a wet noodle for a period of time till the imbalance is strong enough to finish it off. Remember everytime a cylinder fires it puts a tremendous amount of force on the crank as to actually create a spring effect at the journal. This is why the balancer came about anyway. Shear force and not enough harmonics control weaken the crank sure , but the imbalance is what finish them off. My opinion by the way from all the observations. Makes sense but in a real wild it would need to be proved to hold water. I don't have the resources to set that one up.
Cummins also has rods bigger than our pistons and are only going up and down. Far less angular force in every direction. Ford don't make enough power (I have a couple) and there rotating assembly is pretty stout, and don't run as much compression, timing, there pretty conservative as for the intake it's a close design bet it's much for centered and flows fairly well in comparison.
Oh and I was going to add, what about the cylinder balance system? Any chance it could go bonkers and create unequal cylinder pressures ? As far as I know neither ford or dodge have a balance feature like the duramax either?
I think Port intake balance is a possible cause of the harmonics as well as firing order and possibly other factors. As mentioned earlier in the thread though it really isn't all that common.
I'm highly doubting that intake balance is the problem with breaking cranks. Banks probably said this to sound smarter than the rest of us after we figured it out with the help of socal and finfers. I wouldn't stress over it..
Your probably right , but the gears in my head want to figure out a problem and keep running diagnostics anytime the word crank,piston, cylinder, break, cam are heard, said or read..... and as I'm just starting my new build its in the back of my mind on what to change or how to change things so I don't draw the oh so unlucky card. I'm plagued with the not knowing the outcome ocd. I don't gamble or bet, hell I will come close to running a pop machine over for taking my money without producing a soda. Ha ha. As I've been tearing this motor down I've been looking at a lot of the parts and really there's nothing that jumps out. Even with the intake except that the inlets are not centered. Which in theory with adequate volume shouldn't be a problem. Unless like the fuel rail shock when a injector fires, it sends a wave outward from itself creating a flow restriction. Reason they put the super small orfices in the feed side...... is that possible with a gas like it is with a liquid? There both being compressed and would it be greater with a lesser amount of force as it is with greater force?
No just don't drive it like a high school kids with a brand new license and things last. Don't exceed it's intentions and problems will be greatly lowered. Even then stock breaks....
I just popped the heads off this motor and both front pistons are clean. All the rest have the usual black coating. The front 2 pistons are so clean you can see the intake valve circles on the piston surface still.
All 8 of my piston's looked the same. Mine broke at around 180000 miles behind number 4. Stock trans so the tuning wasn't ridiculous.
I don't believe air flow is the issue at all or cylinder pressure testing done in the past would indicate this. A good balance job and changes to the firing order which change the way the crank is loaded seem to alleviate the problem and make it run smoother. That's where I think the improvement in harmonics comes from, not how the air flows into the cylinder.
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I don't believe air flow is the issue at all or cylinder pressure testing done in the past would indicate this. A good balance job and changes to the firing order which change the way the crank is loaded seem to alleviate the problem and make it run smoother. That's where I think the improvement in harmonics comes from, not how the air flows into the cylinder.
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What? The Duramax is 16.0:1 compression, and the PowerStroke is 16.1:1 compression. To be clear: that means the Ford has higher compression than the GM. EDIT: Google lied to me. The Duramax is 16.8:1, so the PowerStroke is lower compression. I am not sure I would call Ford's intake "centered", as they use reverse flow heads with the exhaust in the valley, and the intakes on the outside of the motor. Look it up. Pretty neat. GM had it in the mini-Duramax they ended up discontinuing before it hit production.
I know for a fact at least Dodge does (though they call it "cylinder contribution", and I bet Ford does as well. There is no way this feature could cause damage to the crank, even if it hit the max of +15mm3 on one cylinder. If you are idling, and stab the throttle, the next cylinder to fire will get north of 30mm3 of fuel, causing over 2x the stress a malfunctioning balance rate ever could. Besides, people have had injectors hang open, providing continuous ridiculous amounts of fuel and not break a crank, they just torched the piston.
The pistons should all look the same. If you have difference, there is a problem with the fuel injection or something similar. Also, there should not be any intake valve marks on the piston surface. There is a lot of clearance from the factory. If the valves hit the pistons, there is a mechanical problem or the motor was seriously over-revved (north of 6k RPM typically).
I agree, the only time airflow would be so uneven as to cause significant cylinder-to-cylinder power variations would be off boost, and there is no way you can make enough power to hurt the crank without boost. Excluding the few manufacturing flaw cranks that can and do fail at any power level due to a defect or inclusion, of course.
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I'm not aware of any stock duramax that is 16:1.
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Oh, you are right, it is 16.8:1. That's what I get for trusting Google. Still, I doubt 16.8:1 can cause any problems when most old diesels ran much higher compression than that.
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