Hello,
Here is something that works for me. Place the belt around the motor pulley first. Then take start the belt on the big pulley. Once you get the belt started, clamp it on with vise grips that way it won't slip off. Alot of washers have new belts that seem too short. This is what the factory guys guys suggested to me and it works everytime.
With the belt started on the bigger pulley and clamped on, just start rotating the big pulley and spin the belt on.
It may be tough, but the vise grips will prevent the belt from popping off when you are trying to rotate the pulley to get the belt over the big pulley.
Remember, place the belt around the motor pulley first then start it on the tub pulley. Clamp it on the tub pulley and rotate it on.
Let me know how you make out. I will be more than happy to help you further.
Bill