Yes. It's a rpm thing. In a tractor they probably never go higher than 2000rpm. Automotive the problems start over 2000rpm.Even if that engine came from a tractor?
I have in YouTube videos seen they are getting up to 3500 rpm. But you are right about harmonic balanser. I have seen in "videos" they have swapped tractor harmonic balanser to a car fluid harmonic balanser to prevent crank breaking. Maybe balancing the rotating assembly in the engine could be a preventive factor so the crank shaft does not break.Yes. It's a rpm thing. In a tractor they probably never go higher than 2000rpm. Automotive the problems start over 2000rpm.
6 cylinder diesels need a crank damper on the front to stop harmonics at higher rpm. It's the harmonics that eventually break cranks.