That 6 cylinder crank, slows a classic harmonic fatigue break. Middle of the crank, starting at the oil hole drilling, to spread out to the webs. I guess it would have had the flywheel/damper combination replaced with the drive gear.
In a boat the engine runs at a constant speed, that in this case, looks like it was right on the cranks undamped resonance.
Have they checked the other engines crank?
Harvey.
