hi i have a mercedes v220 cdi auto ?

Rule of thumb with drive belts. if you can twist it 90 degrees, and no more, about the normal direction of movement, at the point furthest from the cogs then it is probably roughly tight enough.

usually there is some kind of nut type assembly that allows you to wind on the pressuse on the belt by means of tightening a nut. i would tighten it until it meets this 90 degree rule of thumb and give it good couple of tightens after that. then go for wee drive, watching your battery lamp. if the battery is being drained ie alternator not working, then the battery lamp will flicker or come on full.

if no lights come on just keep an eye on it for a while until you are confident it is working ok and not putting too much pressure on the cog bearing.

Liam
September 2009