The figure 50 refers to oz-in (ounce inches). It is the amount of imbalance of the crank piston assembly (in ounces) multiplied by the distance off centre. You can’t tell by weighing the parts. The imbalance is counteracted by fitting the appropriate flywheel that has the correct balancing weight. If you fitted a 28 oz-in flywheel to a 50 oz-in engine there would be real bad vibes man!!