Mass balancing mechanism and assembly method

A mass balancing mechanism for compensating mass forces and/or mass moments of inertia of an internal combustion engine, said mass balancing mechanism comprising two compensation shafts rotatable in opposite directions and further comprising a traction drive which connects a driven pinion of a crankshaft of the internal combustion engine to drive pinions of the compensation shafts through a chain or a toothed belt, and for producing a rotation of the compensation shafts in opposite directions, a spur gearing with first and second meshing spur gears is arranged between one of the drive pinions and the associated compensation shaft, the first spur gear being connected rotationally fast to the one drive pinion and the second spur gear being connected rotationally fast to the associated compensation shaft, and a rotatable eccentric bearing having a rotationally fixable eccentric raceway having a central axis about which the one drive pinion and the first spur gear rotate, the eccentric raceway is rotationally positionable to allow adjustment of a tooth flank lash between the spur gears.