I just changed my alternator and put a new drivebelt on. I compared the old drivebelt with the new one size wise and the new one seems a little tighter. Tried to put the new drive belt on and the only way I could was by screwing off the tensionner and screwing it back on but it doesn't seem to go as far as with the old drivebelt. I noticed a pin sticking out of the back of the tensionner and a hole in what it screws on and I imagine the pin has to fit perfect in that hole.
My question: Is it normal the new drivebelt is a little smaller than the used one or did the auto parts clerk give me the wrong one ?

 

I just recently replace my drive belt and tenisoner and idler pulley and I didn't have any problems with mine fitting. I know the guy at the parts store didn't ask if I had AC or not so I told him it had AC because I knew there was a difference.

Another thought does your new alternator have the same size pulley as the old one did?

 

ALWAYS check pulley sizes on anything you replace..

Those are compressor pulleys, you were given the belt for the new one there.
Dayco 5060950 Just at 95"

You need the belt for the old one
Tell them 6K950 Which is actually 95 5/8"

If it WAS a Dayco.. do yourself a favor and get a gates or other brand. Dayco has noise problems WELL documented here.

If possible always buy replacement belt by the old belt #

 

I realized there was a 3/8" drive square hole in the belt tensionner and managed to fit this new belt on. Not sure if it will be too tight but when for a test drive and seems OK. I will inquire for this 95 5/8" one anyway.

 

!!!! Well, yeah!
Good thing you werent putting a belt on a 90's ford! Need a breaker bar for those.
You're probably fine, then. New belt needs just a little effort to slide up over the idler with the tensioner all the way down - That's the one you fit last, btw
If it was like that.. forget the other belt

 

Pettyfog,
I checked the belt brand I just bought: it is a Gates 060960, 13/16" x 96 5/8" made for Napa auto parts.
Now I am faced with another problem ( this 97 blazer is really starting to get on my nerves now) : when I started the engine to see if this new drivebelt and alternator worked ok, I heard a big bang coming from the blower motor just as if something had gotten stuck in the fan fins. Blower now makes a buzzing noise if I try to use it and no air is coming out of it. Did I blow the resistor now ? The blower is about 3 months old.
I have to add that the piece I cut off in order to get to the blower motor broke in pieces cause it was cold outside
(-20C) so I never covered that area after. I can't really see how an obstruction could have gotten stuck in the fan from that opening.