Xantia Mk.2 1.9 TD, oiled underside of the A/C compressor.

[Stewart(oily)]

The size will be printed somewhere on the back of the belt, ie 1736mm by six rows wide, also look at the tensioner pulleys to observe whether any of them appear to be keeling over. sabotage ? a flying stone ? who knows ?

[CitroJim]

I wonder why the belt's in that condition. Could have been damaged during original fitting maybe?

Could be the tensioner has failed and is exerting uneven pressure on the belt. Easiest way to check the tensioner is to eye it and check it is sitting properly parallel to the belt run and not cocked off at an angle. It'll be easy to see.

If it is the tensioner MUST be replaced along with the belt.

There are two belt sizes deepening on what compressor is fitted a 1725 and a 1740 but I can't recall which is which now the longer one I think is for the Harrison (not Harrison as shown in parts lists!!)

Thing is the longer belt will fit the Sanden but it'll be too loose and will flap around wildly.

Failure to replace the belt risks it breaking and snagging the cambelt and quite possibly destroying your cylinder head.