Belt noises - too loose?

I'm sure this will be the dumbest question I've asked for at least a couple of weeks but ...


... What I presume is the alternator belt squeals on start up and when first setting off, stays quiet when under load, and then chirrups like a cage of angry canaries when I've come off the power and am letting the engine braking do its thing.

I've had a quick look and the vertical part of the auxiliary belt that's accessible has maybe an inch of 'push' in it if I apply finger pressure to it.

IiRC belt deflection should be... 9mm for 10kg of pressure?? (this may be totally wrong!) so I'll need to tighten it up?


If that's correct, I will adjust the alternator outwards to apply more tension to the belt, to hopefully fix the noise issue.


I sort of worry that so much pressure on the crankshaft end (from the belt pulling the end) will pull it out of alignment, but then I guess it's designed to take it... lol

I just don't want to overtighten it and cause a problem!


I need to change the alternator anyway because its bracket has worn away and it's not sitting straight now... so hopefully it will be a 'two birds with one stone' fix.


Many thanks in advance, wise people!