Why use a longer serpentine belt on an 850?

greasefingerss · Post by **greasefingerss** » 27 Jan 2007, 19:46

I have made an observation and would like some feedback. This is regarding the serpentine belt. There is a longer belt for the 850 engine that provides better surface contact with the alternator. The original belt configuration only contacts the circumference of the alternator by about 90 degrees. The longer one contacts it with 180 degrees, but at the expense of removing surface contact with the a/c compressor. The a/c compressor originally has 180 degrees of belt contact but with the new longer belt, it gets reduced to 90 degrees of contact!

In my opinion, since the a/c compressor is a greater load (mechanical resistance) than an alternator; I prefer the original design (shorter belt).

Am I missing something? Have I had too many beers tonight?

The link below from Bay 13 is a visual comparison of the old & new belt lengths. The picture on the right is the one I have an issue with.
http://volvospeed.com/Repair/850_serp.pdf

larryh · Post by **larryh** » 27 Jan 2007, 20:24

is that a fact? that the ac is a greater load than the alternator? i guess it doesn't really matter how much contact there is though, as long as it's enough contact to run the part.

..think the longer belt would last any longer?

cocka · Post by **cocka** » 27 Jan 2007, 21:57

I seem to remember reading somewhere that Volvo/Porsche or whoever it was, came up with the setup to ease the load on all the pulleys involved, the later 70 series actually dropped one of the pulleys completely.

Post by **luketrash** » 27 Jan 2007, 22:30

Also, you use the AC when it's hot outside and the serp belt is warmer. I've only had belts start to slip when it's really cold outside. And it's of a higher priority to keep the electrical system charged than to keep the car cool inside

I have no basis for my answer other than I imagine the importance of the alternator working takes precedence over the AC compressor working. The pulley size of the alternator is smaller and takes more belt 'grab' to give it a spin, especially at higher speeds.

Free2drive! · Post by **Free2drive!** » 29 Jan 2007, 08:48

Hi

Yeah it is odd!, I asked my parts guy about this in 2003 and he said the probably reason was manufacter, the longer size is more commonly used not just by Volvo but other car manufacturers and so is cheaper to produce, rather than lots of varying sizes.

I don't know if this is fact but it kinda makes sense.
Matt