A valve train for operating a cylinder valve assembly for an internal combustion engine comprising a valve bridge (VB) including a casing (CS) wherein is slidably inserted a lost motion assembly (LMA), wherein the lost motion assembly includes an outer plunger (OP) having a longitudinal development (X) arranged to receive a main rocker arm action and to transmit such action to the valve bridge through a locking element (LE), wherein, said outer plunger (OP) includes an axial cavity (CV) where an inner plunger (IP) is suitable to slide in response of oil pressurization; the lost motion assembly being configured to define a clearance (CC) between a bottom portion (BP) of the casing and a bottom portion (BP1) of the outer plunger (OP) configured to receive pressurized oil and wherein said casing (CS) is provided of a passing through opening (MO) to discharge said pressurized oil in such a way to dump a sudden restriction of the clearance (CC) caused by lost motion activation.