This paper presents a methodology for numerical investigation of a full flexible balancer drive together with engine and crank train under realistic operating conditions where shaft dynamics, gear contact and rattle impacts, gear root stresses and friction losses in bearings and gear interaction are taken into account and can be balanced against each other to achieve the design criteria.Gear rattle is driven by the speed fluctuation of the crank train, the resistance torque (mainly friction), shaft inertia and the backlash in the gears. The actual trend to engine downsizing and up-torqueing increases the severity to rattle as engines are running on higher combustion pressures. This increases torque and speed fluctuation, which makes the detailed investigation in this torque transfer even more demanding.A common method to reduce gear rattle is the usage of so-called scissors gears. The layout of those gears has significant influence on the gear durability and the overall losses, which requires a detailed and precise model to find the best compromise for the spring stiffness and preload.The investigation is shown for a modern Inline 4-cylinder Diesel engine, equipped with a 2nd order mass balancing system and scissors gear between the crankshaft and the first balancer shaft. The change of gear contact loads, gear rattle, root stresses and balancer drive losses versus the operating range is presented and discussed. Sensitivity analysis of gear profile data and parameters of the scissors gear is performed.This methodology allows the engineer a precise layout and detailed design of such system to reduce noise and losses and avoid gear failure, considering main and contra-dictionary effects, and within reasonable time.