Turn upside down. From front, remove the thin piece of housing below door.
Take out the front 3 screws either side of dryer base. slacken off the fourth ones but don't remove them. Likewise, don't remove the screws that attach the base to the back.
Now you can see and have room to get into the motor and pulleys.
The front of the dryer will pull away just enough for you feed the belt over the drum.
Slacken off (being careful not to remove them) the 3 screws that hold the motor to the base. Then pull the belt in between the 2 pulleys onto the motor.
Tighten the 3 motor screws to take up the slack.
Tighten and replace all screws. Job done
Roy Claxton (Scotland)
September 2006