Aasco flywheel is here.

[Cloudsurfer]

Originally Posted by insite

okay, this is driving me nuts. what would drive a harmonic in this engine that the DMF could actually balance out?

what i'm getting at is that this is a flat 6. it has inherent mechanical balance of 1st and 2nd order. further, the CG stays constant about the crank. the rocking couple of each bank is balanced by the other bank. harmonic balancer or no, this simply shouldn't happen w/ this configuration.

there could be some torsional harmonics, but the 1st order torsional (due to the engine pulses) is inherent to engines in general, since they create torque. IMO, this is just as well damped by a sprung clutch than by a DMF.

finally, the DMF is at the wrong end of the crank to really damp any higher order harmonics that may appear......


HMMMMMM: Jake - did the broken X51 crank come from a car with a solid clutch disk, or a sprung clutch disk?

If I remember it was from a LWF flywheel, tho I don't remember if it was a sprung disc or not.

I played it safe when I built my motor, and I have a dampened crank pulley on a dynamically balanced engine with a LWF and sprung disc.

[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:

[mattatk]

Jake,
CH-46, good on ya!
I had the pleasure of flying CH-47 in Australian Army, but we did all our initial & maintenance test flight training in Ft Rucker, AL & Ft Lewis, WA.
I was VERY impressed with US Army guys & their teaching! I'm sure the Marines set just as high a standard.
I wish we had guys like you working on Porsches in Australia.
All the best,
Matt