Just this past weekend I was coming home from a fantastic drive along HWY 1 and the fan belt light came on. I pulled over to see my fan belt shredded and spat out. It still had a few cords intact but it got ejected in between the other two belts and came completely off and deposited into the rear of the engine bay (luckily it didn't take the other two belts with it). I had another belt but no tools to do the job so had to do the whole tow/spend the night/repair shop ordeal, on Memorial Day Monday to boot. All went well and I was on the road again in no time but I plan on having the right tools in the car for the next time it happens.

My question is this: Does anyone know the reasoning behind having the cooling fan concentric with the alternator shaft and run with a separate belt? It seems to me a bit odd but surely Porsche had good reasons to do this.

Any thoughts?

 

Oh, heck - when you throw up a jump ball like that, I get lured in like a moth to the blue light -zzzzzZAP!

A couple things get accomplished, from what I can see:
1) It's a great way to get the alternator into (sort of) the cooling air stream of the engine.
2) It makes for a more efficient use of engine bay space/volume. (That volume used now does double duty - alternator and cooling system.)
3) Makes for a shorter belt length(?)
4) It uses a quite proprietary ("Porshe") alternator design that let's you charge ("Porsche!")-$ for replacement. (Just kidding - a little - on that last one.)
5) It allowed for easier tweaking by the factory in year-to-year engine design changes re differential fan and alternator pulley speeds (as opposed to tying the two together, ala the RS hub's mod.) Such differential allows optimum speed for both fan AND alternator.
6) Ummm... it works as good as other, more conventional designs. Mostly. (Except when it doesn't.)
7) It's a helluva safeguard against folks accidently touching exposed poles of the alternator...

(And sorry for your bummer weekend.)

 

+1 X3 on the points above:

Packaging, cooling airflow, and different speeds for the alternator and the fan.

 

It seems like the need for different speeds on the fan and alternator could have been done differently. The speed is highly variable anyway as it's a function of rpm's. A single pulley with a shared shaft could work and all you'd need to do is design the pulley diameters to keep the alternator in it's appropriate operating range and then design the cooling fan accordingly, varying the pitch and number of blades.

By the way, how are cooling fan and alternator at different speeds if the two belts are the same part number and the pulley diameters seem to be the same? Am I missing something?

Someone told me that Volvo used two belts for their cooling fan for redundancy purposes in case one broke, the other belt would still operate the cooling fan (don't quote me on this Volvo example as I haven't verified it).

Oh, and Elbeee, my weekend was not a bummer at all! Things like this are all part of the adventure. Plus I got to check out the Ukiah Brewing Company...great food and great beer...check out the Navarro Yarrow...pints disappear rapidly.

 

The alternator pulley is smaller than the fan pulley.

 

They're at different rotating speeds, alright.
Think about it: if they weren't, why would the fan-alternator bearing ever seize?
But they do.
And you hear about it here, from time to time.

Frankly, *I* was convinced enough (re advantages of a simpler design) to tie the fan and alternator together a year ago - via changing to the RS hub design.
(One belt, no bearing, and no carrying around that #!@*%!! 12-pt spline wrench if ever needed for roadside belt repair.)

Talk about making lemons into lemonade.
Good on you!

 

Hey Lonnie, really great pictorial on the RS hub install!

So, have you noticed any performance improvements?

Where did you get the RS hub?

 

Nope. No performance improvements that I can tell whatsoever.
It's just a whole lot simpler system. That's all I really cared about.
(OK - it's simplicity Does make it look tough. Kinda that stripped down, racy look.)

Mine was from Pelican.

I don't think there's much difference in the various versions of RS hubs out there.
Aluminum bodies... some clear anodized, some black... steel screws...