Will I break this crank?

Lurch59 said

And that is what I think. Take out the forces on the crank that are unbalanced parasitic and harmonic loads. Seems like compressive force from the cylinders transmitted to the crank are known,. but centrifugal forces due to poorly balanced rotating assembly at high RPM are huge. I seem to remember steel is very strong with regard to compressive strength, but comparatively weak with tensile loads. I am not an engineer, but it seems that is what I have read. I had a PhD structural engineer tell me one time, "try it, and see if it breaks"!

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If it were only that simple. Of course, crank balancing is incredibly important. But if you’ve seen how far the balance can be and not break anything you’d have a different opinion.

The crank is constantly twisting and untwisting. The damper is there to absorb those forces.

That’s why I said I wouldn’t do a cast crank 4 inch stroke on 340 mains. There isn’t enough overlap. When there isn’t enough overlap, the crank fails. Or, the crank is so thick through overlap that you needless added weigh when the better option was a steel crank.