Can a 5 mm shorter serpentine belt cause problems?

dkvasnicka

Original poster
Member
Jul 24, 2015
366
Czech republic, Europe
When working on my thermostat I noticed that the belt that's on is a 6PK2320. As far as I know it should be 2325 (mm). Can this cause problems, like engine squealing at high revs, mostly when cold? (I know this can be a pulley but when I had the belt off I tried to spin all the pulleys and none of them was noisy)

5 mm is very little. Can I trust the tensioner to compensate for me or should I change it? (no cracks or anything)
 

smt 59

Member
If your belt is squeeling at cold temps. it is a sign that it requires replacement even though it has no cracks etc.. Replace it with the length that came with the truck to avoid any issues down the road.
 
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xavierny25

Member
Mar 16, 2014
6,323
Staten Island, N.Y
Interesting ....I had a mixed issue with this about 2 yrs ago I had a small squealing going on and for what ever reason it was coming from my idler pully. so I went ahead and changed it out and decided to do the belt aswell.like op stated the new belt is 5 mm longer. Shortly after doing this my water pump went. I changed out the water pump and went back to the original belt but also purchased another belt from rock auto thinking maybe autozone has there belt sizes off but no it to came 5 mm longer then the orginal one on my envoy. Later in the summer that year my ac wouldn't work correctly at all. So having the original belt I put that back on and my ac was working great again. So saying 5 mm don't make a difference is a little odd to me. Just my 2 pennies and what I've noticed.
 
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dkvasnicka

Original poster
Member
Jul 24, 2015
366
Czech republic, Europe
xavierny25 said:
Interesting ....I had a mixed issue with this about 2 yrs ago I had a small squealing going on and for what ever reason it was coming from my idler pully. so I went ahead and changed it out and decided to do the belt aswell.like op stated the new belt is 5 mm longer. Shortly after doing this my water pump went. I changed out the water pump and went back to the original belt but also purchased another belt from rock auto thinking maybe autozone has there belt sizes off but no it to came 5 mm longer then the orginal one on my envoy. Later in the summer that year my ac wouldn't work correctly at all. So having the original belt I put that back on and my ac was working great again. So saying 5 mm don't make a difference is a little odd to me. Just my 2 pennies and what I've noticed.
Wow, that's weird :smile: Given that it's kinda interesting that most - if not all - applicable belts on Rockauto are 2325s. Shouldn't more people experience similar issues then? I'm not disregarding your experience, just trying to wrap my head around it all :smile:
 

xavierny25

Member
Mar 16, 2014
6,323
Staten Island, N.Y
Well ima going to be working on the front end of my envoy on Friday changing out the harmonic balancer fan clutch, motor mounts and shocks. While I'm at it I'll switch back to the 2325 belt and see what happens. I'll attach my freon gauges to see my freon level and the amount of cut in and cut out from the ac clutch. I'll post here if I do have anything to add. But for now it's running with what I'm guessing is the factory belt (2320)
 

coolasice

Member
Oct 27, 2013
1,019
Northern Maine
Weak tensioner could affect the belt if it was longer... I doubt it had anything to do with your water pump failure, but it could affect ac if the belt slips when the clutch engages.
 

xavierny25

Member
Mar 16, 2014
6,323
Staten Island, N.Y
coolasice said:
Weak tensioner could affect the belt if it was longer... I doubt it had anything to do with your water pump failure, but it could affect ac if the belt slips when the clutch engages.
I did forget to mention that I did both the tensioner and idler pulley and belt that day when the idler pulley started acting up. It was something the parts guy at autozone suggested and I did.
 

gmcman

Member
Dec 12, 2011
4,656
Actually 5MM is more difference that one would suspect. When I was helping my buddy install a supercharger on an Explorer we had to go back and forth to the parts store trying to get the correct belt. The belts were measured in MM and we just tried slightly larger belts until they worked. One would be either too loose or not long enough to fit over the accessory pulley.
 
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dkvasnicka

Original poster
Member
Jul 24, 2015
366
Czech republic, Europe
This sucks :frown: There are 2315 and 2325 belts readily available here in the CZ and Europe in general. But if I want exactly 2320 mm I'll have to order it from the US and pay shipping costs equal to/exceeding the price of the belt itself...
 

Harpo

Member
Dec 4, 2011
411
Sweden
dkvasnicka said:
This sucks :frown: There are 2315 and 2325 belts readily available here in the CZ and Europe in general. But if I want exactly 2320 mm I'll have to order it from the US and pay shipping costs equal to/exceeding the price of the belt itself...
Welcome to the euro curse.💀💀👽💩😈😈😈👿

I have to say again that I don't think 5mm would matter on a belt of this type, multiribbed with a tensioner. A V-shaped belt, yes but not on this one.

I had a 2325mm on mine but ordered a 2320 from Rockauto together with other stuff, not that I had any problems with it other than age and normal wear.
 
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gmcman

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Dec 12, 2011
4,656
I agree that 5MM may not make a difference in our platforms, but in regards to belts, mainly serpentine, it's actually a big deal. What happens is the belt takes a different path around the last pulley....it cannot wrap around as far and therefore has less surface area to contact the pulley, sometimes causing slip.

Our tensioner is pretty constant in tension, the less contact you have on the pulley, the more tension you would need.

Again, if you took a pic of the tensioner in its position with the short belt maybe we can see what's going on. The 5 MM shorter might not matter.
 

gmcman

Member
Dec 12, 2011
4,656
You also didn't mention how old that belt is that's squealing. I went out and looked at mine and I agree the 5MM may not make a difference. Could be just worn out?
 

dkvasnicka

Original poster
Member
Jul 24, 2015
366
Czech republic, Europe
gmcman said:
You also didn't mention how old that belt is that's squealing. I went out and looked at mine and I agree the 5MM may not make a difference. Could be just worn out?
Yes, it might. I haven't seen a single crack on the belt but I guess a belt can be "worn out" in other ways too... like aging rubber and stuff?
 

Mooseman

Moderator
Dec 4, 2011
25,257
Ottawa, ON
All alternators for the I6 are the same. There was bad info in parts catalogs for belts which asked if it was a smaller or bigger alternator (130 vs 150A). It wasn't the alternator that was different but the power steering pump between the SWB and LWB. Most catalogs have since been corrected.
 

dkvasnicka

Original poster
Member
Jul 24, 2015
366
Czech republic, Europe
So I put on the new 2325 belt today. Haven't driven it yet, idles perfectly, no lights or noises.

The important lesson is this: after having been on the car for 10 years (I presume), the 2320 belt is actually basically the same length as the new one (judging by stretching them both by hand). In other words, there was no meaningful difference to be seen when I compared them. I guess it just got worn out, stretched a bit...?
So all the worries about the belt being longer are completely unnecessary, IMHO.
 

dkvasnicka

Original poster
Member
Jul 24, 2015
366
Czech republic, Europe
I feel like I should post an update to this.

First of all I had the same experience as @xavierny25 had. My water pump went "rocks in a cup" like 2 weeks after I put on the 2325 belt. The dots didn't connect in my brain at that time but I'm positive the longer belt contributed to it. Second, it's not true that the belts are "basically the same length", as I wrote earlier. It was an error on my part, I just didn't put enough effort into measuring them properly. Sorry for that. Even after all those years, 2320 is still measurably shorter. Third, I got much more vibrations in gas pedal, belt squeal when cold and general lack of smoothness when running the 2325 belt. A few weeks ago I bit the bullet and paid the shipping on a new 2320 belt from the US and installed it. The outcome of all this for me is the following:

1. If your truck runs a 2320 belt and you need a new one DO NOT even think about buying a 2325, thinking 5 mm doesn't matter.
2. If all you ever knew was a 2325 belt and your truck runs OK then... well... it's weird but good for you :biggrin:

Now I'm just wondering why all that confusion about belt lengths. When I checked Rockauto a bit deeper I found out that it does indeed prescribe a 2320 belt for the 9-7X (among all the 2325 belts) but only starting with MY 2008. Did GM change pulley size on any of the belt accessories or did they start using weaker tensioners at that time? Or is it just that they finally acknowledged that 2325 belts are too long and lead to parts loss and changed the spec quietly?
 
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gmcman

Member
Dec 12, 2011
4,656
1. If your truck runs a 2320 belt and you need a new one DO NOT even think about buying a 2325, thinking 5 mm doesn't matter.

Exactly.

5mm is huge. You can always mark the tensioner and see how much the belts change the orientation.

Best bet for serpentine belts is to get them from the dealer. I always use the dealer and recommend the same.

Case in point, my friend asked me to change his belt before they left on a long trip, I said to get from the dealer. They bought from a reputable parts store and the belt fit, no noises when installed. About 3 states away it started to howl, he called me and I said take the old belt I put in your stow away, and have a local shop swap the belt..this will work for time being until you can find a dealer. I said whatever the squeal is, will be the pulley that will fail due to heat , likely a seal.

They didn't change the belt, the water pump eventually failed from a melted seal. Roadside tow for 50 miles then a garage to replace water pump.
 

mrrsm

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"On a Rotating Turntable, How do Tangential Speed and Rotational Speed vary with Distance from the Centre?"

Tangential Speed ... Increases with Distance... Rotational Speed is Constant


You could use either a Carousel or Huge Ferris Wheel as an example to explain why such a small decrease or increase in the length of the belt can be so significant. If you are standing at the Centre of the Hub... making a single 360 Degree Rotation, it feels like a constant, slow and lazy "Turn of Events".

But when sitting on one of the Carousel Horses or while sitting inside the basket of a Ferris Wheel along the OUTER EDGE of the Rotating System... You would have to hang on tight...and squint from the velocity of the Wind in your Face! The larger The Outer Circle becomes... the Faster it has to move to keep up with the hub as it spins at the same slow rate near the Axis of Rotation... in this case..that point is represented by The Crankshaft Bolt... holding the centre of The Harmonic Balancer-Serpentine Pulley.

Here is another Good Visual Representation the Phenomena of Tangential Speed Variance but the device doing the Axial Motion are the Gears in a Rear Axle Differential instead of Belts and Pulleys...Enjoy the Bike Show, Too:


And so... Like the Outer Wheels on Turning Cars and Bikes...The Longer the Belt...The Faster the Outside MUST Move ...and this phenomena has the very real consequence of Making The Water Pump... The Power Steering Pump... The AC Compressor... The Idler Pulley and The Belt Tensioner ... ALL Speed up... or Slow Down depending upon how Large ...or how Small... the Outer Circle becomes inside the Belt.
 
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