Please note the spring has not been fitted incorrectly it should be on the left hand side of the motor in a near vertical position. The picture everyone has been following from this site: www.wikihow.com showing the belt is fed round the black tensioner wheel and motor is wrong! The spring should not be changed, as then the belt will potentially be rubbing on the electirc wires.
The belt should go round the drum, now following the belt down the left hand side of the drum, it should then go straight under the motor shaft fitting on the grooves, then round the left hand side of the black tensioner wheel, then back up round the right hand side of the drum. This will then pull the motor in the other (correct) direction putting tension on the spring in the correct direction.
John Mackinder, January 2008