Abstract: A viscous torsional vibration damper of the kind operating on the shear film principle has an annular shaped housing providing an annular working chamber within which is mounted an annular complementary inertia mass ring and a viscous damping fluid substantially fills shear film spaces between the working surfaces of the inertia ring and confronting working surfaces of the housing within the chamber. The cover has one or more lugs extending from the outside of an axially extending wall that engage with lugs inside the housing near the bottom wall. Rotation of the cover relative to the housing causes an axial force through the lugs that forces the cover into sealing engagement with the housing.