Sorry about my bad english, but i hope you all unerstand.
One of most common problem with alfa diesels is noisy aux belt tensioner. If you buy all new original parts its also an pretty expensive.
Bearings 6301 (2pcs)
Some spanners (also 15 and 32)
Die cutter (M12)
First take off right front wheel and take inner plastics off (dont know the right name
Then open the hood and take upper pulley off, with 13 spanner, then its easier to take belt off.
Take nr 32spanner and take tension off the belt.
Using the torx, take off the big engine pulley, you dont have to touch the middle bolt.
Then undo the 3bolts that holds the tensioner shock in place.
Undo the hex bolt and you got out the belt tensioner.
Theres one pulley left, using the nr 15 spanner, remove that also.
Take the bolt out that holds tensioner pulley in place.
Then hammer or press out old bearing, keep in mind, that we have tou use the pulley afterwards.
If you got out old bearing, then put new ones in place.
Beacuse theres no bearing that has 10mm inner diameter, so we had to use bearing that have 12mm inner diameter. So we have to use M12 bolt to hold new bearings in place.
Drill new hole and make new M12 thread inside.
Then put washer between pulley and bracket to aling it prefectly
Repairing upper pulley:
Press or hammer out old bearing.
Bearing only comes out to one side, other side has lip on its way.
Then pun new one back in and its done.
Go to carstore and get a new one!
Putting all back:
Put tensioner back.
Put belt back on alternator and steering pump.
Put back upper and lower pulleys.
Pull belt on A/C pump
Put crank pulley back on.
Using nr 32 spanner, wiggle the belt back on.
Then tension lower pulley.
Try it and dont forget to put wheel back on before taking it for a ride.
I hope it helps.