Date: Fri, 12 May 2017 16:59:51 +0000
Reply-To: Dennis Haynes <d23haynes57@HOTMAIL.COM>
Sender: Vanagon Mailing List <vanagon@gerry.vanagon.com>
From: Dennis Haynes <d23haynes57@HOTMAIL.COM>
Subject: Re: Screeching Alternator Belt
In-Reply-To: <DC2C84C1-6AF9-4EA8-88D0-64A9C0AEEA87@shaw.ca>
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Alistair,
Thanks for the vote of confidence.
Ron,
Books could be written on the short comings of the Waterboxer alternator drive belt design.
I'll start with the basic trouble shooting and then move on. The belt squealing or screeching is due to the combination of the belt slipping/gripping on the pulleys and the tension being such that it sets up a resonance. The basic fix is a combination of increasing tension and/or getting a better wedge drip-surface friction change etc. to increase the belt to pulley friction enough to transfer power to the alternator. From experience, most people do not tension this belt properly. To make things worse this is a specialized belt application and off the shelf belts are just not designed for this service. The OEM belt was a custom not just for the size, but also the cord reinforcement and covering. How tight should it be? If you are lucky enough to have a 91 with the teeth drive tensioner you tighten that to 6 ft. lbs. If not, the belt has to be tight enough that you can use the alternator pulley nut to turn the engine through the compression strokes without slip. This belt drive has to transmit power. If it can't hold back you hand turning a wrench to turn over the engine it won't work well the other way turning the alternator at speed under load.
How much power? If you have 90 amp alternator, at 14 volts you are trying to produce 1.260 watts (1.26kw). The alternator is not 100% efficient, maybe 75%. We know they make a lot of heat. So at full load lets just say we need to transmit enough torque and speed to produce 1.575kw. By definition 1 HP = .746KW. So this simple single belt drive needs to be able to transmit ~2HP to always do whatever the alternator may want.
In a "perfect world that size belt is probably limited to a 3HP application. But wait, some engineers designed in failure and others signed off on it. In designing belt or chain sprocket systems you want the belt or chain to wrap around as close to 180 degrees as you can to get max power transfer. With modern serpentines systems with idlers we can get even more. However on the Waterboxer, we don't even get 90 degree wrap around the crankshaft pulley. So to get the belt to wedge in and actually drive the load you need the perfect wedge fit, a lot of tension, a wear resistant high friction belt casing and a reinforced belt that won't stretch. Also, you need pulleys wear the v-groove has not worn smooth or oversized. Good luck!
In the industrial world pulleys are considered consumables and they get inspected for wear and surface finish. We generally don't even consider that for automobiles. Most automotive belt drives have enough reserve to do what is needed with ease. The Waterboxer alternator belt drive is an extreme "Opps". I guess the water pump placement removed all options except to go to a serpentine system with idlers. I guess too much cost.
OK, now back to fix. First make sure all the brackets are tight and the alternator bearings have not failed. A common failure is the back bearing (non pulley end) the have the insert fail between the bearing and housing This will cause the alternator rotor to tilt causing both a loose belt and pulley miss alignment. Over time this will also cause broken brackets and those studs in the case. When bad enough you may even get some strange noises when the rotor hits the stator in the alternator. Try some different brands of belts. I find that for some customers the Gates 7430 or 7435 work very well. Different brands seem to have slightly different dimensions. I am experimenting with some industrial belts but just haven't gotten a trusted combination of size and v-groove angle.
Hopefully some of this will help with understanding of the problems here. Since the alternator and water turn so easy by hand we don't realize how much force is needed to make the alternator actually produce power. Also, it turns a lot faster than the engine. That belt set up is challenged to say the least.
More questions, let me know.
Dennis
-----Original Message-----
From: Vanagon Mailing List [mailto:vanagon@gerry.vanagon.com] On Behalf Of Alistair Bell
Sent: Thursday, May 11, 2017 11:57 PM
To: vanagon@GERRY.VANAGON.COM
Subject: Re: Screeching Alternator Belt
Ron,
I'm sure Dennis will give you the right answer here, and goodness knows you have the choice of belts, but the correct belt in my experience solves things.
I've tried a few belt sizes and manufacturers, belts that don't squeal in my experience have been the ones that sit lower in the pulley.
And double check the pulley alignment.
Cheers
Alistair
> On May 11, 2017, at 6:02 PM, The Bus Depot <vanagon@BUSDEPOT.COM> wrote:
>
> The alternator belt on my '87 Westy screeches horribly at idle, and
> sometimes when you first pull out from a stop. (It stops if you gun
> the engine, or while driving at almost any speed.) Replaced the belt
> and the new one started doing the same thing after only a few hundred
> miles. The belt tension is correct. The mount looks okay and nothing
> seems visually wrong with the geometry. The alternator does not seem
> to be binding. One of the pulleys had a bit of surface rust but
> sanding it off made no difference. No hot spots when viewed with an infrared heat detector. Running out of ideas.
> Any thoughts?
>
> Ron Salmon