TD5 Bottom pulley troubles

Has anyone got a cutaway diagram of how the bottom pulley is on a TD5 Defender?

On tickover its making a knocking noise thats coming from the bottom pulley.

I took the weight off the end of the pulley to find the actual fan belt drive ribbed part wasnt actually secure, it could rotate freely through around 40'degrees.

Is that how they all are? Mine seams to have side to side play in the ribbed peice also

Any help appreciated

thanks

That dont sound right.

All it was in the end was a large rubber "bush" had come unstuck from the inside of the bottom pulley, a good wash and a tube of superglue later its back working and hasnt proven to be a problem yet, 4days later