Crank Balancer snapped off (Whipple 2.9)

Black Dog

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I wonder how many did OPG's as well. The stock balancer would have had to come off and could be reinstalled incorrectly/not seated.
^^^ Exactly. Turbos aint snapping crank snouts. Everybody that does big power does TCG and OPGs. Pulling and installing Balancers aint the easiest of jobs. Shit happens.

 

shogun32

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Wouldn't you and @engineermike agree that reducing the parasitic load in the form of weight, driven by the crank snout will increase snout life?
the snouts and more importantly the various accessories placed on the snout don't fail for lack of torsional rigidity, the strength of the key/keyway, or the uneven acceleration/deceleration per se. Though in some cases they appear to. In fact you could make a naĂŻve case for massively adding to the weight to significantly change the amplitude of the accel/decel forces.

I would first and foremost look at the quality and precision of the snout support bearing(s) and overhang and address that.
 

80FoxCoupe

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In heavy duty machinery applications, you don't take credit for the second key. On a microscopic level, it's impossible to get both keys to carry the load simultaneously. Are the dual keys situated 180 apart?
Yes, 180 apart.
 

80FoxCoupe

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the snouts and more importantly the various accessories placed on the snout don't fail for lack of torsional rigidity, the strength of the key/keyway, or the uneven acceleration/deceleration per se. Though in some cases they appear to. In fact you could make a naĂŻve case for massively adding to the weight to significantly change the amplitude of the accel/decel forces.

I would first and foremost look at the quality and precision of the snout support bearing(s) and overhang and address that.
Generally speaking, yes or no?
 

shogun32

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Generally speaking, yes or no?
I'm going to say 'no'. Too many variables and the important ones, axial position of the weight (how far away from the support AKA bearing) and the precision and width of the bearing(s) is where the majority of investigation and remediation should be focused. And removing all radial forces acting far away from the support - AKA belts under heavy/excess tension. Tighter is not better.
 

Epiphany

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I like to disassemble things.
v8er said:
If it would’ve gotten loose, I would’ve done that, remove the bolt, clean it up and than reinstall
Not to belabor the point but the bolt wasn't loose (can't remember the last time I've heard of red Loctite failing) and you said you checked the torque and it was good. What you actually did was check breakaway torque and subsequent prevailing torque.
 

80FoxCoupe

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I'm going to say 'no'. Too many variables and the important ones, axial position of the weight (how far away from the support aka bearing) and the precision and width of the bearing(s) is where the majority of investigation and remediation should be focused.
Ok so generally speaking, adding load in the form of weight driven by the crank snout does not contribute to reducing crank snout life. Got it.

Thus, reducing load in the form of weight driven by the cranks now does not contribute to increased snout life. Got it.
 

shogun32

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Ok so generally speaking, adding load in the form of weight driven by the crank snout does not contribute to reducing crank snout life. Got it.
I said no such thing
Thus, reducing load in the form of weight driven by the cranks now does not contribute to increased snout life. Got it.
why are you stuck on this simplistic world-view? Lighter by itself is not righter. If I make a damper half as heavy but moved 1/2" further outboard it could easily be orders of magnitude worse than the stock config.
 

80FoxCoupe

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I said no such thing

why are you stuck on this simplistic world-view? Lighter by itself is not righter. If I make a damper half as heavy but moved 1/2" further outboard it could easily be orders of magnitude worse than the stock config.
Im not stuck on anything, just looking for some answers. Just haven't found any yet.
 

olaosunt

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Are people snapping Boss cranks too?
They are no different from the coyote .
The 5.2 crank used in the 5.2 Alluminator/predator and the FP350S engine is said to be stronger
 

shogun32

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They are no different from the coyote .
The 5.2 crank used in the 5.2 Alluminator/predator and the FP350S engine is said to be stronger
and I expect they have better/tighter/more bearings.
 

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People that buy turbos to avoid the potential chance of breaking the snout are too funny. Considering you’re many times more likely to experience a bearing or ring land failure.
 

shogun32

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People that buy turbos to avoid the potential chance of breaking the snout are too funny. Considering you’re many times more likely to experience a bearing or ring land failure.
I don't see how SC vs Turbo changes cylinder pressures or risk of ring damage if given the same band of pressures.
 

engineermike

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....just looking for some answers. Just haven't found any yet.
Anyone on this forum who claims to know this particular answer is either flat wrong or basing it on the same sparse failure data that you and I already have access to. Like I said, there are very few people globally who really know how to answer this accurately.

When dealing in rotational harmonics, consider the following: The crankshaft has a torsional stiffness and a moment of inertia, as any spring-mass system does. If you were to hold one end steady, twist the other end, then let go, it will vibrate rotationally at some frequency. But in use, the first torsional resonance will be both ends moving opposite each other with some "node" in the middle that's turning at basically constant speed. I'm going to make 2 huge assumptions for simplification: 1) that they don't want it ever operating at resonance (this isn't always true but I suspect it is in this case) and 2) the first critical speed is the one we are trying to avoid.

The idea, then, would be that you want the maximum forcing function to be below the first torsional resonance by some margin. The forcing function is simple and possibly just 4 x running speed, or about 30k cpm (7500 rpm x 4 power strokes/cycle). Therefore, you need the rotational natural frequency to be something like 33k cpm or higher for a 10% separation (rule of thumb). You can see why Ford said years ago that increasing the rpm or power (forcing function frequency or amplitude) would increase failures. Torsional natural frequency of the crankshaft can be increased by reducing moment of inertia on either end (not to be confused with the damper's "inertia weight") or by stiffening the middle, which generally isn't an option. The damper contains either an elastomeric element or a viscous fluid, coupled to a mass. This changes the dynamics of the front of the crankshaft by basically attaching a spring-mass-damper to it, which of course must be selected (spring rate, mass, and damping coeffient) to effectively counter-act the motion and increase the natural frequency of the system. This is one reason that a lighter damper might be a bad thing; because the internal inertia-mass is probably better if heavier.

If the above were all there was to it, I might could figure it out myself given a couple of weeks. But the truth of the matter is I grossly oversimplified it in the above explanation. You'd have to figure in the rod big-end weight, rotational effects of the torque converter and even transmission input shaft and oil pump, consider amplitude of the forcing function, factor in the all the accessories (each one being a spring-mass-damper), factor in the 4 cams and chains (more spring-mass-dampers), consider multiple mode shapes (>1 nodes), consider running above the first resonance, oil damping in the bearings, and even consider temperature effects on the properties of the elastomer or viscous fluid in the damper. Then of course, run the model through a matrix of all possible engine speeds, power levels, and temperatures. I bet that there is a small engineering group at Ford that does this full-time for all the engines in development, and they have the software modelling and hardware testing capabilities that the aftermarket can only dream of.
 

 
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