Patent ID: 7690624

Claim:
A valve drive device comprising: a stem nut for screwing a valve stem thereinto; a drive sleeve engaging with a male spline formed on a peripheral outer surface of said stem nut, said drive sleeve including a worm gear on a peripheral outer surface thereof; a worm in meshing engagement with said worm gear; and a housing that supports said drive sleeve by a bearing, wherein said valve drive device further comprises: a stem nut fastening member having a first male screw that engages with a female screw provided on a peripheral inner surface of said drive sleeve; and a locknut that engages with a second male screw provided on a reduced diameter portion of said stem nut fastening member, said second male screw having a reverse screw thread relative to said first male screw, while a flange being formed at an upper end of said locknut, said flange being abutted to an upper end surface of said drive sleeve, so that no slack may arise between said stem nut fastening member and said drive sleeve.