sgrice may be correct - you may need to loosen the compressor mount bracket to get enough access to mount the tensioner.

You'll also need to be creative in terms of getting the pulley and its shaft installed - I had to remove the pulley from the shaft to get enough clearance behind the radiator to get the shaft inserted through the compressor bracket and into the tensioner.

__________________
Wayne
2005 BMW X5 3.0d (b 02/05)
2001 BMW F650GS Dakar (b 06/01)