Technical Cambelt change - quick question, hopefully !!!

[Dezbo]

Hi,
Just about to change my cambelt and tensioners on my Fiat Ducato 2.3 Multijet (MY2010). I have purchased the crank/camshaft locking pins and thought I was good to go - but I have seen that I need to also loosen the camshaft pulley before belt removal. Any idea why I need to do this? I thought the idea was to lock everything in place?
This is shown at 2.11 minutes in to the youtube video below.
"Secure the camshaft pulley and slacken its fastener. The pulley should be able to rotate around the camshaft end while remaining centered."
www(dot)youtube(dot)com/watch?v=d1yN9rI2PZM

 

[Pickup]

Haven't watched the video but usually where the pulley is slackened it is so the pulley is effectively free to rotate.

The cam(s) are locked in EXACTLY the right position and the pulleys are free to move slightly. If the pulleys couldn't 'float' then the cams would have to rotate (out of exactly the correct position) to compensate for any variation in the the belt.

Then, with the new belt fitted and tensioned, when the pulleys are tightened on the cams you know that the cams and crank are in EXACTLY the right alignment.

HTH