Originally Posted by GlenL

Anyone care to address the question of why automakers went to the serpentine belt? Might shed some light on using one.

Having dealt with these on several cars, one reason is that it allows the engine to be packaged more closely into the engine bay. There's no stack of pulleys for different belts and the engine block can wedged that much closed to the fender wall. Transverse mounting, you see.

When I saw this thread I thought "why the hell would anyone want that?" I'm with the naysayers in that multiple belts are more reliable, overall. A failure analysis would show that it will have more failures, but during each failure there are fewer subsystems affected. The power steering is separate from the alternator and I only need one belt left to spin the fan.

Originally Posted by Hacker-Pschorr

No kidding. That is like pointing out if the car runs out of gas it stops running.

My point is, with four different belts if something "gets in there" and breaks a belt you've got a 1 in 4 chance the only belt that will disable the car might survive.
With a single belt goes, everything stops spinning.

I'll take those 1 in 4 odds, and yes I've been there when something took out a serp belt in an Audi.
Also a serp belt has a lot more surface area and small areas for crap to get into and cause damage (which is what happened to my Audi)

I have also been where one belt breaks and takes out one or more others... on a 928... your 'odds' are not realistic

Yes I know it's possible to lose any belt in any system. Just saying this blanket statement that one belt is always more reliable and better odds than multiple belts I do not agree with.

One belt is more reliable. It has been proven over and over again. The automakers would not use it if it was not reliable.

It's great when you are on vacation in the middle of nowhere and the pulley on the single tensioner system decides to go flying down the road.
This was a low mileage Yukon too.
How much has to be "wrong" in order for an alternator belt to come flying off or break outside of deferred maintenance on a 928? Debris getting in there? Does this car have all the belly pans installed?

Can't comment on that specific situation, but my anecdotal evidence shows otherwise. I have never seen a pulley come off but I have seen all the ***** come out of the bearing and still run. Made a hell of a noise, but still worked. For an idler to fail is either an installation issue or ignoring the noises under the hood issue

Spare parts "just in case" consists of a few belts in the trunk and a 10/13mm wrench.
The equivalent spare parts with a serp system is a couple pulleys and a tensioner along with the belt and in the case of my Denali, more than two wrenches depending on what broke.

In what world would a tensioner be required? If the tensioner goes it gives you ample notice. Just need to listen once in a while. Even you know that.

As for my Denali, the serp belt also turns the water pump, if the power steering pump catastrophically failed (like it did on my friends truck) and you are dumb enough to drive until the battery goes dead....you just cooked the engine.
Yup.....that's a brilliant design.

Give me a serpentine driven water pump any day over a timing belt driven one. Especially when the pump costs 600$


On every car ever made? I don't think so.
A friend of mine is currently dying with a serp belt tensioner on a Neon. Whole thing is seized up and the replacement part is a $200 bracket combo system that includes the tensioner.

How often are belts changed? All the time, energy, and engineering to fix a problem to speed up a once in 5+ year service?
I have yet to touch a 928 accessory belt unless I was also doing a timing belt.


I am NOT trying to say serp belts are not reliable or somehow inferior to separate belts. I'm not going to covert my Denali to separate belts anytime soon.
Every system has it's pro's and con's. When people bring up such a project, they tend to only focus on the pro's and forget the con's.

I simply do not agree there is any real advantage to doing such an upgrade on 928's.




No argument there, but I see this "fix" along the same lines as cutting a hole in the fender to make the clutch master easier to replace.
I'd like to kick that engineer in the junk for that one, too


If someone does this I'll applaud the effort and it would be interesting to see, but don't sit there and tell me how much it will improve the reliability of a 928, I'm not buying that.

And here is where I agree. Very much like the tensioner for the timing belt. The factory system WORKS. Why fvck with it? It's part of the reason I haven't bothered trying

How many have you changed? Here is a brief write-up on changing the serp belt on my Saab:



Here is the full write-up:

http://www.fixmysaab.com/9-5_repair/...o.asp?nsteps=3

I like this part: "You need two people to compress the tensioner. One to compress the tensioner and a second to insert the hex key into the hole."

Oh yea.....light years easier than the accessory belts on a 928.


Why doesn't someone bump up the thread on converting the 928 timing belt to chains because those are so much more reliable too?
Chains are much better idea than a timing belt. But you need to have it in an oil bath or pressure spray. My F150 4.6 litre had 400,000km and never had to be opened for any timing service anything. and one water pump too.

Originally Posted by GlenL

Anyone care to address the question of why automakers went to the serpentine belt? Might shed some light on using one.

Having dealt with these on several cars, one reason is that it allows the engine to be packaged more closely into the engine bay. There's no stack of pulleys for different belts and the engine block can wedged that much closed to the fender wall. Transverse mounting, you see.

When I saw this thread I thought "why the hell would anyone want that?" I'm with the naysayers in that multiple belts are more reliable, overall. A failure analysis would show that it will have more failures, but during each failure there are fewer subsystems affected. The power steering is separate from the alternator and I only need one belt left to spin the fan.

Originally Posted by UpFixenDerPorsche

From a manufacturer's perspective, cost, in both original manufacture, and in parts inventory. One belt instead of four, and the less costly crankshaft pulley, makes a $$$ difference...

Originally Posted by siscogts

More reliable?who snapped a traditional V belt? 2 or 80 percent of owners ?
Apart from guessing why porsche engineers haven't seen this "problem"....
Can't be bothered, sorry.

Originally Posted by GlenL

Yep... I'm an engineer in new product development and deeply understand that goals and constraints drive product development. "It's better" has got to be followed by a long list of why's and tradeoffs.

How about... "It's smaller, it's lighter, it's cheaper and the reliability meets the target. It will last until the warranty expires."

Originally Posted by UpFixenDerPorsche

From a manufacturer's perspective, cost, in both original manufacture, and in parts inventory. One belt instead of four, and the less costly crankshaft pulley, makes a $$$ difference.

If a manufacturer can reduce the total component count, the trickle down effect reaches as far as the car dealer in that less floor space is needed to keep the spares for that model car, and to the maintenance/repair costs for that vehicle. One serp belt is easier to change than four. Even the WSM can be smaller/cheaper

As for reliability and probability of failure I think the manufacturers make sure they have done their homework. After all, if you've produced 2 million cars and the serp belts begin failing left, right, and centre, it's a very deep ugly hole you have to escape from, and it can quickly reach the point where the more units sold the deeper the hole gets.