Lightweight Crank Pulley Check-In

[dsm-onster]

I don't think this analogy applies. Yes the theory of resonance is sound, but that doesn't mean it's the dominant stressor in a crank. There was a good link posted to EvolutionM forums that showed it takes over 600hp on a 7 bolt EVO crank before early wear of the bearings showed up when using a solid pulley. The HP level matters because it affects the magnitude of the vibrations. BTW the EVO 7 bolt crank uses narrower main and rod bearings than a 6 bolt crank, so the bearings don't give as much support, and the EVO crank is 2 pounds lighter.

Early bearing failure occured after a track run or two. . . at 600hp. We're talking the flexing of the crank over thousands of miles. . . at 300-400hp. 'The engineers engineered the crank so well that it needs no damper'. Then they installed one at 200crank horsepower.

 

[pboglio]

These type of longevity mods can't easily be proven to work, not by us. You'd need to slap an engine on a dyno and run it 24/7 for a month to do life cycle testing. This is how it is done when we need to test a part to 1 million cycles at work, parts being sent to an outside test facility.

Typically, when you design something you'd need to get material data on fatigue strength, which is rarely published. The fatigue strength at "x" cycles can sometimes be as low as 25% of the 1x yield strength of a test specimen. The higher the cycles, the lower the yield strength due to crack propagation. Techniques like shot peening, electropolishing, or in this case I believe nitride carbiding definitely helps to hold the part closer to its 1x yield strength. That means you'd need to design with a large safety factor just to make it last for "x" amount of cycles.

I've done a bit of fatigue failure testing, as well as designing to prevent. Interesting stuff, but designing for resonance is fairly sophisticated and I sure as hell wouldn't attempt to second guess the factory. Only thing I wish is if they could design a damped pulley that wouldn't separate like clockwork at 60,000 miles

 

[Locke]

I don't think anybody in here said that using a solid pulley will cause your crank to break, instantly or otherwise, rather that using a solid pulley will increase the risk of such things occurring.

Sure there is, here's a recent quote saying just that, "
Likewise, we know that ringing parts at their natural frequency can be disastrous."

"Will" implies something is definite. "Can" implies that it is able, but not definite.

Funny.

 

[DashLaflash]

Anyone else notice that in the link dsm-onster posted, and MachV Motorsports experience involved a 2.3l stroker engine. I wonder if that greatly increases the chances of issues with a solid crank pulley? It might also be the reason why the nissan sentra 1.6l doesn't come with a damper pulley from the factory.

 

[1990AWD]

As a mechanic, we were taught that the harmonic balancer is there to help with the vibrations of the crankshaft. It does help, but I do not believe it would cause an engine failure by itself. How many of those cranks that broke were either: 1. pushing more than factory HP, 2. how many had a lightened flywheel, and 3. how many had the balance shafts removed? The flywheel, balance shafts, and harmonic dampner ALL work together to keep the engine running smoothly and with minimal vibration. You start taking those things away, and yes, you could break a crankshaft.

On a side note, how many of those crankshafts were broken under normal driving, and how many broke during a hard launch? I am an agriculture mechanic and have seen crankshafts break in inline-6 engines on big four-wheel drive tractors making 2000 lb-ft of torque simply because the operator lets the clutch out too fast, an with all the traction in the world, something has to break.


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[dsm-onster]

Anyone else notice that in the link dsm-onster posted, and MachV Motorsports experience involved a 2.3l stroker engine. I wonder if that greatly increases the chances of issues with a solid crank pulley? It might also be the reason why the nissan sentra 1.6l doesn't come with a damper pulley from the factory.

don't tell the 7bolt lovers!!! They won't have a reason for craddling their stock girdle at night

 

[907gs-t]

I run the Unorthodox lightweight pulley system on my 98 GS-T with no ill effect's to my ride.

 

[DashLaflash]

don't tell the 7bolt lovers!!! They won't have a reason for craddling their stock girdle at night

You can make a 2.3l stroker out of a 6 bolt as well though . I was mostly referring to the fact that issues are more likely on a stroker engine than a 2.0l. Or at least the possiblility of issues.

 

[dsm-onster]

7bolt-huggers love their girdles. . . Pevents crank movement; primarily jumproping. Just poking about crank movement. They love the girdle because they think it makes their stroker swaps they will never do invincible . . . Please, don't kill my lame joke.

 

[pneumo]

Instead of posting pics, vids and CAD drawings of flimsy structures failing, and the inevitable comparison with the 4G63 crank, I thought I'd show the real thing.

This first pic is the side view. Note the overlap between the main journal and rod journal. The stroker crank has less overlap in this area.

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The area where the main and rod journal overlap is also the thinnest part of the crank, at least from a side view, so here's a look from the front. Check out the flared lobe between the main and rod journal, it's thickest at the same point where the main and rod journal meet. That's a great way to reinforce the crank and add stiffness in a critical area.

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[SpawnedX]

What no one seems to bring up about these and the other incidents (all discussed in great depth in a thread on NABR for those who have access). Is that of the 3 examples brought up, all 3 of them were machined cranks, I don't know how much material was taken off, but the cranks that snapped all were "weaker" than the others.

As a mechanic, we were taught that the harmonic balancer is there to help with the vibrations of the crankshaft. It does help, but I do not believe it would cause an engine failure by itself. How many of those cranks that broke were either: 1. pushing more than factory HP, 2. how many had a lightened flywheel, and 3. how many had the balance shafts removed? The flywheel, balance shafts, and harmonic dampner ALL work together to keep the engine running smoothly and with minimal vibration. You start taking those things away, and yes, you could break a crankshaft.

1. Irrelevant, both 2.0 and 2.4 cranks are manufactured in the exact same fashion with the exact same metals. Both have been proven to hold over 1,000 HP with-out breaking, both dampened and un-dampened.

2. A lightened flywheel or a non-lightened flywheel are irrelevant as well. Neither of them are dampened, all a dampener does is absorb dangerous harmonics.

3. Balance shaft removal is also irrelevant, all balance shafts do is provide rotational mass to one side of our motors to offset the fact that our rotating assembly is not perfectly centered, which causes vibrations. It's for comfort purposes only.

---

Great, so let's talk facts, because in the end facts > your opinion (yes you, you know who you are).

What is an harmonic damper pulley?

First things first, we do not have a "balancer" pulley. Our engines are internally balanced. Don't believe me? Ask those who work on these cars all the time. I recommend FFWD, they do a lot with rotating assembly work. So if you use the word balance in this argument, your point is moot, because you clearly have no idea what you are talking about.

Our stock crank pulley is by definition a harmonic damper. A very inefficient one at that. In fact I would be willing to bet that once you increase HP on your car at all, there is no dampening happening from that pulley. The rubber ring on that pulley, which does not fit over the snout to make a direct absorption pad, is in charge of absorbing harmonics caused by combustion and violent pushing of the rod on the crank and dissipate them.

Since our pulleys actually require the harmonics to pass through the crank, then the crank bolt, then finally into the dampener, it's effect is almost negate. In fact, aluminum being a soft metal, does have it's own dampening properties to it. In fact with how little dampening our stock pulleys do, I would be willing to bet that the harmonics effects are handled almost identically between both pulleys.

What are harmonics? Why are they bad?

Harmonics are sound waves. Every item on earth will shatter to the proper sound wave, reaching the proper pitch. Think about an opera singer, who sings in high enough pitch to break glass. This is the same concept.

The metal in our crankshafts also have a sound pitch that can cause instantaneous shattering. Our engines are capable of making that pitch during combustion at certain RPM levels. Harmonic dampers are designed around what those particular ranges are for their current HP levels. Therefore the moment you start adding power, you almost fully negate that dampening effect on your stock pulley, because the RPM range these dangerous harmonic pitches occur at.

If the right environment takes place, the right pitch on a pulley that fails to absorb it, the crank will shatter at it's weakest point, which will almost always be flywheel side on our cars.

Are there other causes possible for the damage we are being shown?

Yes, it's something we should all know about. Detonation. When the piston is sent firing back down too early, the crank absorbs the pressure and shatters. It is much more common than a harmonic damper failure, especially in turbo-charged cars pushing big numbers. It also happens a lot in improperly tuned cars.

If your crank had to be machined due to previous engine damage, you increase the likelihood of this happening. Take a 1 mm thick metal rod and a 2 mm thick rod, apply pressure, see which one bends under the lower pressure point. It's pretty simple. Shaving the material down also changes the inherent harmonic properties of it, which is why real race teams just replace cranks.

Can this happen on any dampened and non-dampened pulley?

Yes. The end.

Can we prove the failure was due to harmonics or other causes?

Nope. You never will know.

Does this happen often?

Considering I can only find 5 DIFFERENT example on every forum I argue this about. Plus of those 5, 4 of them were turned cranks, I am going to say this is super rare. Yes, crank-walk is actually a more common occurrence.

What should I buy?

The big boys use lightened, aluminum pulleys. At the end of the day, I take their knowledge and experience as proof over the many over-opinionated, undereducated, cheap and scared people of the internet.

I use a Fluidampr, in short the gel like material inside the damper can absorb and dissipate harmonics over a wider range and faster than a rubber based damper. However, I wouldn't be scared to use an Unorthodox, which I have, with no ill effects.

The choice is yours.

 

[dsm-onster]

1. Irrelevant, both 2.0 and 2.4 cranks are manufactured in the exact same fashion with the exact same metals. Both have been proven to hold over 1,000 HP with-out breaking, both dampened and un-dampened.

Nope, 2.4 cranks are always jump roping more than 2.0 cranks. That's why we have the oem 2g girdle and the kiggly girdle.

2. A lightened flywheel or a non-lightened flywheel are irrelevant as well. Neither of them are dampened, all a dampener does is absorb dangerous harmonics.

Nope. The fly wheel is the "ground", where the shocks radiate FROM. When you have more weight you guarantee that the shocks get all sent the other way. That's why I and even you run a damper. Because it's better than running a huge fly wheel on both ends.

3. Balance shaft removal is also irrelevant, all balance shafts do is provide rotational mass to one side of our motors to offset the fact that our rotating assembly is not perfectly centered, which causes vibrations. It's for comfort purposes only.

Yes

 

[SpawnedX]

Nope, 2.4 cranks are always jump roping more than 2.0 cranks. That's why we have the oem 2g girdle and the kiggly girdle.

My 2.4L block comes with the exact same girdle as my 2.0L, I am not following you here.

Edit: I think you are talking about a 6 bolt thing. However, the manufacturing process is the same. The jumping comes from the larger stroke which puts more weight on the outside of the crank which I guess "throws it out of balance." That's really the best I can think of to what you are referring too.

Nope. The fly wheel is the "ground", where the shocks radiate FROM. When you have more weight you guarantee that the shocks get all sent the other way. That's why I and even you run a damper. Because it's better than running a huge fly wheel on both ends.

The shocks mean nothing, it's the harmonics that do the damage.

 

[dsm-onster]

If the shocks are stopped then there is no harmonic generated. If the shocks are lessened, there is less amplitude in the harmonic. Yes resonance spikes the amplitude VERY quickly. But you also are lessening the effect of a node and thus how much twisting effect of the resonance takes place, when you lessen the weight of the fly wheel. It's like turning a wrench when a nut is fully tight. You need more torque, because the resistance of the nut is greater (like the resistance to move of the flywheel). As the nut loosens, less stress is placed on the wrench; less torque is required; less resistance, like the smaller resistance to move from a lighter flywheel.

As I said, the fly wheel grounds one end and sends the shocks forward to number one. If the weight that the shocks radiate from-- the inertia (resistance to move) of such weight allows the force from the piston to bend the crank-- is lighter, then you'll have less flex at number 4 which transfers less flex to number 3 which transfers less flex to number 2 which transfers less flex to number 1.

You also mention this:

The metal in our crankshafts also have a sound pitch that can cause instantaneous shattering. Our engines are capable of making that pitch during combustion at certain RPM levels. Harmonic dampers are designed around what those particular ranges are for their current HP levels. Therefore the moment you start adding power, you almost fully negate that dampening effect on your stock pulley, because the RPM range these dangerous harmonic pitches occur at.

Horsepower, or perhaps you mean cylinder pressure, alters the range of harmonics? You said that the value of the shock means nothing. . . But really you don't alter the resonant frequency of a glass by raising the volume. So you cannot mean that the increase in cylinder pressure alters the rpm point of resonance for a crank. So does the initial magnitude of the shock mean nothing or not?

Therefore, yes flywheel weight is very pertinent to the conversation.

 

[SpawnedX]

If the shocks are stopped then there is no harmonic generated. If the shocks are lessened, there is less amplitude in the harmonic. Yes resonance spikes the amplitude VERY quickly. But you also are lessening the effect of a node and thus how much twisting effect of the resonance takes place, when you lessen the weight of the fly wheel. It's like turning a wrench when a nut is fully tight. You need more torque, because the resistance of the nut is greater (like the resistance to move of the flywheel). As the nut loosens, less stress is placed on the wrench; less torque is required; less resistance, like the smaller resistance to move from a lighter flywheel.

As I said, the fly wheel grounds one end and sends the shocks forward to number one. If the weight that the shocks radiate from-- the inertia (resistance to move) of such weight allows the force from the piston to bend the crank-- is lighter, then you'll have less flex at number 4 which transfers less flex to number 3 which transfers less flex to number 2 which transfers less flex to number 1.

You also mention this:



Horsepower, or perhaps you mean cylinder pressure, alters the range of harmonics? You said that the value of the shock means nothing. . . But really you don't alter the resonant frequency of a glass by raising the volume. So you cannot mean that the increase in cylinder pressure alters the rpm point of resonance for a crank. So does the initial magnitude of the shock mean nothing or not?

Therefore, yes flywheel weight is very pertinent to the conversation.

Maybe, I am just explaining it poorly.

Fluidampr® How it Works Page.

That should clarify it some. Let me try to as well:

1. The more horsepower the engine is outputting, the stress on the crankshaft increases, and the harmonic frequency range that becomes destructive are seen at different operating levels then from what the "tuned" harmonic damper Mitsubishi provides us with. So, since you can increase power with-out replacing flywheels, you are not doing anything to protect yourself from this. That since by theory and argument, your "tuned" damper is already being negated, that avoiding switching out the flywheel over this is silly.

2. The argument you are making, which is correct, is that by changing the rotational mass, you change the harmonic properties. I agree and understand now what you mean, my apologies.

What I am trying to say is that either which way, unless you stay 100% stock, the stock damper really isn't doing it's job. Therefore using the solid aluminum pulley is probably no less dangerous.

In the end, I used the Fluidampr, because I am an anal retentive clown, who likes to get as close to 0% chance as possible.

 

[Locke]

Changing the power output of the engine (increasing cylinder pressure) won't change the natural frequency of the crankshaft, rather only the level of the magnification to the amplitude of the resonance.

 

[SpawnedX]

Changing the power output of the engine (increasing cylinder pressure) won't change the natural frequency of the crankshaft, rather only the level of the magnification to the amplitude of the resonance.

I think we are basically saying the same thing. The cylinder pressure increases changes the harmonic resonances it creates at different HP ranges, this is all I am saying.

 

[ramsack]

From what I see you two aren't saying the same thing. Locke is saying it's the frequency is what harmonics is about. SpawnedX is saying it's the amplitude. Well the frequency is what sets it up. This would be the rpm/firing phase. Amplitude is what is the other factor. Harmonic resonance happens regardless of the amplitude. The amplitude would be the factor that when it reaches a certain level would destroy whatever is resonating.

 

[Locke]

1. The more horsepower the engine is outputting, the stress on the crankshaft increases, and the harmonic frequency range that becomes destructive are seen at different operating levels then from what the "tuned" harmonic damper Mitsubishi provides us with. So, since you can increase power with-out replacing flywheels, you are not doing anything to protect yourself from this. That since by theory and argument, your "tuned" damper is already being negated, that avoiding switching out the flywheel over this is silly.

I was directing my previous statement at this, specifically. Of course, I may not be understanding the statement fully. I'm not really interested in this conversation and my attention wanders.

The ranges that the resonance become destructive do not change (without altering the crank itself), this is a matter of the natural frequency of the crankshaft. As power increases, the amplitude of the resonance increases at all points. The areas closest to the natural frequency (and it's matching divisibles) will of course be the most dangerous, but danger increases all over. So what becomes classified as destructive force because of added power will be over a far wider range than at stock power levels. Is this what you're getting at, Michael?

 

[SpawnedX]

I was directing my previous statement at this, specifically. Of course, I may not be understanding the statement fully. I'm not really interested in this conversation and my attention wanders.

The ranges that the resonance become destructive do not change (without altering the crank itself), this is a matter of the natural frequency of the crankshaft. As power increases, the amplitude of the resonance increases at all points. The areas closest to the natural frequency (and it's matching divisibles) will of course be the most dangerous, but danger increases all over. So what becomes classified as destructive force because of added power will be over a far wider range than at stock power levels. Is this what you're getting at, Michael?

Yes, thank you for wording it better for me.

 

[dsm-onster]

Ok so. . . we've come to the conclusion that more power increases the negative effects of resonant frequencies. . . And that the stock damper is meant to stop them but may not be enough. So get a better damper. . . Great! like we're all saying, for the insurance of your crank, run a damper.

 

[SpawnedX]

I think it would be good to have someone sift through this information and compile the facts and make it a tech article and stop these posts from ever coming back.

 

[DashLaflash]

Ok so. . . we've come to the conclusion that more power increases the negative effects of resonant frequencies. . . And that the stock damper is meant to stop them but may not be enough. So get a better damper. . . Great! like we're all saying, for the insurance of your crank, run a damper.

I think this sums it up pretty good. It's safer to run an aftermarket damper but with such a low occurance of crank failure the undamped pulley is fine to run. Aftermarket dampers are designed for such a wide range of frequencies anyways is it really that effective on our engines? I built a 7 bolt and took my chances with crankwalk... maybe some day I will take my chances on an undamped pulley.

 

[Locke]

I'll try to sum up this whole thread by using quotes from pg 1 of this thread:

The damage that can (and has, on the 4g63) potentially happen is catastrophic. Imagine spinning your engine at 6500rpm (or whatever) when your crankshaft breaks. If you're lucky, you may salvage the pistons and some low dollar parts, but the rest of the shortblock would be irreparable.

Some 4g63's run without harmonic dampeners for years without problems, then some explode. It's a risk, and you know the stakes. If it's worth the risk to you, do it. I'm not going to stop you.

To add:

I'm by no means saying not to use one. I'm saying to weigh the risks and use your own judgment. Breaking cranks because of this almost never happens.

For me personally, the gain is not worth the risk. My 1g got a new stocker when the previous one failed.

 

[DashLaflash]

I'll try to sum up this whole thread by using quotes from pg 1 of this thread:

Haha ya but look at all the fun we had .