Hi, thank you for contacting JustAnswer.com. My name is Russell. I will do my best to provide the right answer to your question.
Sometimes you have to have the belt on the capstan, before you can anchor down the motor with the screws or bolts. This ensures sufficient tension on the drive belt.
Or are you having a different sort of problem with the positioning of the belt onto the capstan wheel?
If you can photograph the region of the difficulty, and post it to me with your reply, it might help me understand and advise you better.
Since I appear to be making no progress on this case, I must, with apologies, Opt Out of this case in favor of a different Expert here, who may have an approach to the problem that suits you better... and at no additional charge.
Thank you for your patience meanwhile.