A selectable mass flywheel assembly for a powertrain of a motor vehicle includes a first mass and a second mass. The first mass is connected to a crankshaft of an engine and the second mass engages with a clutch to transfer torque from the engine to a transmission. The two masses are rotationally coupled to each other with a spring and damper assembly. The flywheel assembly further includes a locking mechanism that engages both masses during the startup of the engine to lock the two masses together to minimize the vibrations and pulsations in the powertrain during startup of the engine.