alternator belt too short

was getting the cambelt and aux belt changed the other day and my mechanic rang to say that the alternator belt was too short? rang Renault and they reckoned it should be right but said that they would order in another kit to make sure Renault hadn't accidentally put in the wrong belt. Rang Renault today to check the numbers on the belt and they are the same as the belt I already have?? Anyone had this problem?? Gonna tell the mechanic tomorrow that it should definitely be right, but he compared the old and the new and said it was considerably shorter??
 
Do they have a tensioner? I can sort of see that they could stretch over time and the tensioner would take up the slack.
 
Is it too short against the old belt or too short they can't get it over a tensioner?
 
polley v belts dont really "stretch" they just normally snap

some fords use a "stretch" belt but these dont use a tensioner

i wonder if the cup (non-aircon) and ff belts are the same??
 
I said to the guys at renault about the aircon etc and they said they were looking up the part for my car using my number plate??
 
he was looking at where he was working the other day and there was an alternator belt for a bora lying there too and he reckons he may have compared it with that belt by accident.
 
Erm no offence but are you sure this is the right guy to be doing your cam belt? If he cocks it up then best case is poor running, but more likely is a knackered engine.
 
He's a good mechanic does work on all type of cars, hoping he just compared the belt with the wrong one, I have my car back, cambelt done car running well.
 
Glad you got it sorted mate - but I'm waiting for the 'my engine went pop' story to come from this...really hope not though.