I think I may need some help here:

One of my belts is gone and I need to buy a new one, but I am not sure of the name or the part number. This is the one in green on the sketch below.

Does some one know the name or part number for a 1971 LS5 (454) ?

Also, the actual setting of the belts is not as shown in the assembly book (above) but as shown on the sketch below: The same belt in red goes around the crankshaft, the water pump, the generator and the steering pump. It looks to me it is not standard. Does some one know where I can find such a belt ?

Looks pretty wierd.  My 71 doesn't have the Air and no idler pulley.  I hae two belts, one for the waterpump and alternator, the other just for the PS pump.  I'll check my AIM tonite if someone doesn't get in before me.

Your A/C should just be an additional belt from a thrid pully slot from crankshaft to waterpump to A/C I'm presuming.

The green belt is the "idler" belt. They were only used on big-blocks w/ A/C, to my knowledge. It was needed due to the extra load on the w/p by the A/C compressor.
The upper diagram looks correct to me.
The lower diagram looks like someone just put a belt on willy-nilly. In that configuration, neither the alt, or the P/S pump will have the correct tension to operate properly.
Maybe some here with a little more big block info will chime in

I bought the car 3 years and a half ago and had no problem with the P/S pump nor with the alt. They both work OK. I hadn't notice the weird configuration until I had this "idler belt" broken.

I did not find the term "idler belt" on the web sites (neither Eckler's nor GM). Where do you think I should look at ?

Christian38902.9644907407

Check with Quanta, they have/manufacture most all of the reproduction belts.
If you have the AIM, it will give the original GM part #. The Quanta site also gives the orig. number as a reference.
Any other big-block folks out there wanna jump in on this?

The top is correct. I just changed my belts when I replaced the water pump. The belts from Quanta are very good and original, they fit perfectly. A bit pricey but it is worth the extra expense. bcliff38903.3384490741

 

Not sure if this will help..

www.C3VR.com/member_uploads/6801_6900/6820/belt2.jpg 

http://www.C3VR.com/member_uploads/6801_6900/6820/belt1.jpg

http://www.C3VR.com/member_uploads/6801_6900/6820/belt3.jpg

2 cruzn38903.6647453704

Duoh!  I gotta keep looking to see if people are talking about SBs or BBs.

[QUOTE=Chips58] Duoh!  I gotta keep looking to see if people are talking about SBs or BBs.[/QUOTE]

Christian, did you ever figure out the belt you need  I have a 74/454 with AC I'll try to go to my garage and see if I can get any info for you.