Hmm, I haven't looked at this forum for a while...
Well I suppose you could check that you have the right length belt.
(ZAN1258288008 1975mm)
Other things I can think of could be that the spring that maintains belt tension has broken or fallen off - you can test this by moving the jockey wheel it should bounce into the position of higher belt tension. The spring should hook into the base of the machine.
Another possibility is the jockey wheel itself which should not have any furrows worn in it.
If the bearing had worn out really badly, I suppose the drum could be too low.
The belt should be running on the grooved section of the axle.
Final thing I can think of is that the drum might be sticking a bit, ours does this occasionally, and sometimes I can fix it merely by rotating the drum manually half a turn.
BobG
October 2004