A push-pull chain type window actuator with an elongated and slim housing. The actuator is slim enough for mounting inside a window frame. The housing includes a chain path in communication with a chain exit. The push pull chain is engaged by a sprocket that is driven via a transmission by two or more electric drive motors in tandem. An auxiliary axial bearing supports the drive shafts of the electric drive motors. The transmission includes a worm gear. In order to extend the life span of the wormwheel the thickness of the teeth of the metal worm is chosen to be significantly less than the thickness of the plastic wormwheel. A resilient stop block dampens the halt of the push-pull chain at the end of the outward stroke.