Aasco flywheel is here.

[greggp]

I tend to agree with insite. There are numerous torsional forces in any internal combustion engine, the pulsing of the engine upon firing of each cylinder is easily heard as a car idles ...and the mechanics are the same at higher rpms, but not as noticeable to our ears. The absolute need of a mass damper to avoid breaking a crank seems pretty remote, but I guess it is possible - depending on what the crank is made of..

I would expect this would have everything to do with crank manufacturing techniques and engineering. There will always be resonant frequencies that every crank wants to vibrate at, and this is true in the torsional direction too. How compliant the crank is in the torsional direction is what matters, as also at what frequency the crank wants to recoil at when a torque load is released.as speed increases the the rotational forces will certainly cross that frequency and the crank will be excited. A billet or even a forged crank will by it's nature have a higher natural frequency than a sintered metal crank. They are also much stronger because of the way they were manufactured.

Personally I am not a fan of sintered metal cranks, I believe they are more likely to fail in torsional loading scenarios.
Are the cranks that have failed, all been sintered metal cranks?

[Cloudsurfer]

Originally Posted by greggp

I tend to agree with insite. There are numerous torsional forces in any internal combustion engine, the pulsing of the engine upon firing of each cylinder is easily heard as a car idles ...and the mechanics are the same at higher rpms, but not as noticeable to our ears. The absolute need of a mass damper to avoid breaking a crank seems pretty remote, but I guess it is possible - depending on what the crank is made of..

I would expect this would have everything to do with crank manufacturing techniques and engineering. There will always be resonant frequencies that every crank wants to vibrate at, and this is true in the torsional direction too. How compliant the crank is in the torsional direction is what matters, as also at what frequency the crank wants to recoil at when a torque load is released.as speed increases the the rotational forces will certainly cross that frequency and the crank will be excited. A billet or even a forged crank will by it's nature have a higher natural frequency than a sintered metal crank. They are also much stronger because of the way they were manufactured.

Personally I am not a fan of sintered metal cranks, I believe they are more likely to fail in torsional loading scenarios.
Are the cranks that have failed, all been sintered metal cranks?

Unfortunately, all M96/M97 cranks are sintered

[insite]

Originally Posted by Cloudsurfer

Unfortunately, all M96/M97 cranks are sintered

indeed. still, very bizarre that this happens. cloudsurfer - harmonic balancers are normally tuned to damp the natural frequency of the crank. who designed the damped pulley, & do we think it's tuned?

i wish i could get that broken crank under a microscope.......still, with it being sintered, it would be a lot harder to tell exactly what happened.

[Cloudsurfer]

Originally Posted by insite

indeed. still, very bizarre that this happens. cloudsurfer - harmonic balancers are normally tuned to damp the natural frequency of the crank. who designed the damped pulley, & do we think it's tuned?

i wish i could get that broken crank under a microscope.......still, with it being sintered, it would be a lot harder to tell exactly what happened.

Well aware The pulley I have came from RSS, and was "designed for the M97 3.8 engine to retain the factory damping characteristics" so honestly, who knows if or how well its tuned, but I figured it was better than having nothing, so it went on my motor.

I, too, would be interested to see the actual failure of that broken crank....

[insite]

here's the best close-up on flat6innovations.com: