[25stevem]

Having had a SD 421 990 crank they where a twisted forging and darn heavy even compared to a 455 crank.

[Jay S]

Thanks for the correction Paul, that is correct the Arma is a trade name of nodular steel by GM. I just used it as an example because I consider it among the best of Nodular irons, kind of a bench mark.

I did mention the grain structure of the offshore cast cranks was pretty crappy. The metal is also softer. There is more too it that just yield numbers. Versus watching a big HP engine using a Pontiac OEM crank, I would place to hide if an off shore cast crank was used in a 800 HP+ engine dyno session!

The factory Nodular cranks Pontiac used are very tough, but not compared to a non twist 4340, that was my point, it was not too talk down Pontiac’s factory cranks. It probably sound like it the way I worded that statement. I have almost all N cranks, and one 4340 in my Pontiac cars. Like I mentioned or inferred in a couple other posts, I think the harmonic balancer destroys more factory cranks than over loading them.

Thanks Shiny, good catch, elasticity was not the correct wording, should have use resilience or toughness. Good thoughts.

[Sirrotica]

I think the harmonic balancer destroys more factory cranks than over loading them.

From my own experiences I would agree that statement. Many times a faulty crank is blamed, but harmonics make that part fail rather than what it's made from.

If anyone here has ever observed a diesel engine at idle, and watched the fan belt in the area of the balancer, it is constantly changing speed as each cylinder comes up on compression, and then fires. That speed change is constantly trying to twist the crank forwards, and backwards. A diesel many times can be 22 to 1 compression, so it's roughly twice what a gasoline engine is. That's why it shows up at idle, and can be seen with the eye. Gasoline engines go through the same type of twist motions just at a lesser degree. This is one of the forces the the balancer tries to dampen. Take that dampening away, and material failure happens rather quickly. You'll find the weakest link in the chain

Just springing for a billet, or forged piece isn't any guarantee that the part will survive. The balancer will either lengthen the longevity, or if defective, will shorten the longevity of that shaft. Don't cheap out when it comes to what you hang on the front of that expensive crankshaft.

[Dragncar]

Originally Posted by Sirrotica

From my own experiences I would agree that statement. Many times a faulty crank is blamed, but harmonics make that part fail rather than what it's made from.

If anyone here has ever observed a diesel engine at idle, and watched the fan belt in the area of the balancer, it is constantly changing speed as each cylinder comes up on compression, and then fires. That speed change is constantly trying to twist the crank forwards, and backwards. A diesel many times can be 22 to 1 compression, so it's roughly twice what a gasoline engine is. That's why it shows up at idle, and can be seen with the eye. Gasoline engines go through the same type of twist motions just at a lesser degree. This is one of the forces the the balancer tries to dampen. Take that dampening away, and material failure happens rather quickly. You'll find the weakest link in the chain

Just springing for a billet, or forged piece isn't any guarantee that the part will survive. The balancer will either lengthen the longevity, or if defective, will shorten the longevity of that shaft. Don't cheap out when it comes to what you hang on the front of that expensive crankshaft.

I did not cheap out on mine. I paid 440$ for mine and now they are 663 $

Ductile iron, nodular iron and Arma Steel, all the same thing. Rods and 4 bolt caps made out of it too.


https://harmonicdampers.com/index.ph...1ule6u3li6m4f5

[Shiny]

Regarding harmonic dampers...

Do they have to be "tuned" to the rotating assembly or are they "universal" (within reason)?

My guess is if they are true vibration dampers, they won't care much what they are damping but then again, they are part of a system that's vibrating in torsion so the masses and stiffness of all the components will affect the magnitude, resonant frequencies, and intrinsic component damping.

For example, I expect a cast iron crank to dampen vibe better than a steel crank. Similarly, aluminum rods are a third the stiffness of steel or iron, which has to affect vibe response of the system...

Sorry for the diversion - just going down my overthinking adventure path and about ready to replace the 52-yr-old damper on my car so it kind of popped up.

Mike

[mchell]

Cast crank?

Broke it….