assuming  your machine motor does not have a adjustable gate. 
the  second fitting method is,
apply the belt  centrally to the the small pulley continue to feed belt onto the large pulley wheel, (to the point where it looks to small,) now use the cross arms in the center of large pulley (Watch sharp edges) to continue to turn the belt on,the belt will stretch and jump on .
                
 wirecutterman
                
 May 2010