The dryer belt on my Performa Dryer

The dryer belt won’t stay on the motor. This is a brand new belt I just got yesterday. The belt fits correctly, but the small pully keeps coming off. What am I doing wrong? Also where can I find the diagram or schematics of the inside the machine? They would really help. Any suggestions? Thanks!

Sorry, the model number is: PDET910awy. It is a Maytag and american made as far as I know.
However, I found the answer to our problem on this Forum when I found this diagram. We were putting the belt on backwards. At the time I felt like "DUH!!! you dummy". But now that the dryer is fixed and up and running I can laugh about it and share. I hope it will help someone else on here.

Thank you! Your help here has been really great. I am going to tell eveyone about this forum.