Abstract: A conveyor-chain-drive gear-box and a chain-tensioning assembly comprising main gearing in the gear-box which includes a shaft carrying one of the gears, and auxiliary gearing outside the gear-box adapted to be driven by an auxiliary motor and having a gear wheel. An apertured side wall affords means through which the gear wheel and shaft may be removably connected together. An idler gear outside the gear-box is movable from a position in which it is out of engagement with the auxiliary gearing to an operative position in which it can transmit drive from the auxiliary motor to the auxiliary gearing. A housing is provided which is removably mounted on the side wall and within which are housed the auxiliary gearing and the idler gear.