Serpentine Belt goes bad too soon.

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4 cylinders generally have dynamic balancers[in the form of revolving weights] while 6's have harmonics [in the form of a damped moving mass in the crank pulley].
Huw
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Yes- the latest BMW fours have a separate balance shaft - or maybe even a pair of them.
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Dave Plowman snipped-for-privacy@davenoise.co.uk London SW
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Sixes also have a harmonic balancer.
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Dave Plowman snipped-for-privacy@davenoise.co.uk London SW
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wrote:

I think you need to appreciate the difference between dynamic and harmonic balancers. Harmonic balancers are fitted to most six cylinder engines, are external and mounted on the crankshaft itself, usually invisibly within the crank belt pulley. The internal viscous fluid can deteriorate and the mechanism can fail. With ordinary V belts this failure will manifest itself as a very short belt life. In fact the belts can be thrown within a very short time or will twist inside out on the pulleys despite everything else looking OK. There will be no evident vibration felt by the driver. I would not expect serpentine belts to fail in such a short time frame as a result but they will fail eventually. Crank failure can result if left unrepaired for long.
Dynamic balancers are what make four cylinder engines run smoothly. These are short or long, single or double counter rotating out-of-balance shafts, gear driven to oppose the out of balance forces of the rotating crank. A failure of these through bearing or casting fracture problems will result in much noise and vibration.
Huw
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Since you appear to be replying to me, Huw, I'm well aware of the difference.
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Dave Plowman snipped-for-privacy@davenoise.co.uk London SW
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wrote:

I have not seen fours with harmonic balancers, only dynamic ones. I haven't looked that hard I must admit.
Huw
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Poorly worded, I'll admit. I'd *guess* some ultra high revving ones might well have.
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Dave Plowman snipped-for-privacy@davenoise.co.uk London SW
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Huw wrote:

Most of them do have them (M40, M42, M43, M44, maybe others). They are called "Vibration Dampers" in the parts lists.
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-Fred W

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Huw wrote:

<snipped all over the place>

There are a lot of rubber harmonic balancers out there. A whole lot.
They fail and the belt pulley that is bolted to the weight ring walks outward or wobbles. The outward walk will eat the side off a serpentine belt and toss or twist a V-belt. The wobble can chunk belts.
I still think the OP just has a bad batch of belts... Too old on the shelf likely.
Mike 86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail in '00 88 Cherokee 235 BFG AT's Canadian Off Road Trips Photos: Non members can still view! Aug./05 http://www.imagestation.com/album/index.html?id !20343242 (More Off Road album links at bottom of the view page)
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-0800:

I don't see how. An inline-4 has naturally balanced pistons, provided that the 2 outer cylinders are 360 degrees out of phase (one does compression while the other does exhaust). Then the 2 center ones are 180 degrees different from each of those. So while the outer pair is going one direction, the inner pair is going the opposite direction at the same speed.
Are the crank and cam naturally balanced by symetry in an inline?
The opposite of the inline-4's perfect balance is the inline-2, used on cheap motorcycles. Those things vibrate like hell because both pistons go up and down together. BMW made a huge improvement with the opposing-2 -- they go in and out together but because they face opposite directions they balance each other out.
-- spud_demon -at- thundermaker.net The above may not (yet) represent the opinions of my employer.
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I would not install a gates belt on this BWM. Gates are a good belt, but not on a euro car. Stick with the continental.
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On 7 Dec 2005 09:08:57 -0800, snipped-for-privacy@gmail.com wrote:

see my other post on this topic.
From this guy's anecdotal experiences, I wouldn't touch one if you gave it to me for free.
Lg
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On 7 Dec 2005 09:08:57 -0800 snipped-for-privacy@gmail.com wrote:

Why? A belt is a belt, built according to specs from the manufacturer. (Think: width, length, grooves, and so on). The most important thing is the quality of the materials in the manufacturing of the belt, plus the overall manufacturing process.
I use Gates belts and hoses on my Porsche, Isuzu, Chevy, and Suzuki (motorcycle) - Gates outlasts the OEM.
Just because some vehicle is not made Stateside, doesnt mean Gates cant build a quality belt/etc for it.
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Sam, I'd look closely at each pulley surface, including idlers. Sometimes they wear at an angle towards the center, rather than flat across the original surface--supercharged Buicks have been esp. troublesome in my experience. The idlers have also worn with grooves from who-knows-where ? These grooved pulleys then wear grooves into the belts. HTH, s
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wrote in message> news:_0zlf.26977$dO2.> > I've been having trouble with premature belt failure for a while and can't

Thanks all. Based on the advices, I'll change the idler bearings tomorrow. My measurements came out with a full play of 0.04 inch at the top edge of the idler wheel. If I had a German service manual I'd check this number but the best manual I have is Bentley which is almost too basic and nearly useless. Here's more info on the belt issue:
68k miles 5ft-year... = car bought 76k miles 8th year.. = 2" sections of belt chipped 80k miles 9th year ..= all sections of belt splits, some chip, brand Continental 87k miles 10th year = 1" sections of belt chip, brand Continental 87k 10th year .........= will try to replace idler bearing.
If the effects of the environment is cracking the ribbed part of the Continental belt, which becomes visible only after two weeks of installation, should there be a preventative maintenance done yearly?
Thanks
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On Thu, 08 Dec 2005 08:54:32 GMT, "Sam Nickaby"
wrote in message> news:_0zlf.26977$dO2.

Sam,
Unless this car is designed as a Mars Rover or is going to operate in a Venutian Atomosphere of ammonia, there is zero maintenance that should need to be done to a serpentine belt. Ever.
If you find bearings/pulleys that put uneven stress across the belt, laterally, this could lead to early fatigue of the belt. IOW, the pulleys/idlers _really_ need to be plane-parallel to eachother.
Lg
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Sam Nickaby wrote:

wrote in message> news:_0zlf.26977$dO2.

I am going to take a wild assed guess and figure you bought the belts at the same place.
My next guess is they bought the belts when the car was new or before that even and they have had them sitting on the shelf ever since.
If so, the belts have dry rotted.
I would try to buy the next belt at a different place and even change brands if one there appears dry to the touch.
Mike 86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail in '00 88 Cherokee 235 BFG AT's Canadian Off Road Trips Photos: Non members can still view! Aug./05 http://www.imagestation.com/album/index.html?id !20343242 (More Off Road album links at bottom of the view page)
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Sam Nickaby wrote:

Wow. 4k miles on the belt and it frags? Where have you getting your belts from? Maybe they have been sitting on the shelf too long?
--
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I see on the Car Talk website that someone wrote in with a complaint similar to yours. There conclusion was that the most likely culprit was the crankshaft vibration damper (which has been referred to as the harmonic balancer in this thread). I would think that if yours were failing to the point of causing belt failure that you would be able to see it wobble with the engine running.
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I have had several of these damned things fail over the years and there was never any obvious sign apart from throwing belts.
Huw
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