Belts are usually reliable in all but a few machines. This is despite the fact that for cheapness of manufacture the makers do not provide any means of correctly tensioning the belt, at the expense of shorter bearing life in the motor and drum.
I've noticed belts that are of the correct type & fitted properly, can be ejected by either a deformed drum pulley or play in the drum bearings. This latter is accompanied by NOISE from them.
Repairman, April 2009
