Serpentine Belt goes bad too soon.

If it was a six cylinder model I would agree with you but I don't think there is a harmonic balancer on a four. All things need considering and the most unlikely is a faulty belt. Most likely is a small piece of dirt stuck in the pulley V's somewhere. Even a bit of rough paint would be enough. Then check alignment of pulleys and condition of all bearings. Next check for mounting problems on the belt driven accessories. Also check for undue drag or power consumption from these. Last but very much not least, check that the tensioner spring is in good order and that it is not weakened somehow. I have one engine now where the spring is around half the strength it should be. It is also easy on some applications to install the belt out of square. This applies particularly if say the bottom pulley has more grooves than other pulleys. Manufacturers sometimes standardise on crank pulley sizes but vary the ancillary pulley and belt sizes according to application and load. In this circumstance it is easy for the uninitiated to install a belt wrongly causing undue stress and premature failure.

Huw

It has been years since I've owned a Bimmer but I would think that a

4-cyl. would be far more likely to have a harmonic balancer than a 6, because of the 6-cyl. engine's better inherent balance.

nate

"N8N" wrote >

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

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 (More Off Road album links at bottom of the view page)

Fram uses a _very_ low-grade gasket in comparison with that supplied on the Mobil 1 series filters. In comparison, Fram's gasket ( and other rubber parts ) is something between chewing gum and a rubber band.

There is such stuff as crap rubber. You know this from buying budget tires and comparing the tread-wear and handling characteristics with a higher quality tire. Crap rubber is not ruled out on my list, as a case for premature belt failure. Other people have ruled it out and gone on a witch hunt for something more sinister. Good for them; they must have lots of extra time on their hands.

Lg

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?

The seal isn't the (biggest) weak points of the Fram filters. It's what's inside that is crappy.

Sixes also have a harmonic balancer.

Yes- the latest BMW fours have a separate balance shaft - or maybe even a pair of them.

Absolutely, there are qualities and types of elastomers which are much better than others for certain jobs. And they can age and ozone crack, even when stored on a shelf in some dealership.

I havent bought a cheap set of tires since 1964, when I put a new set of tires on my 57 Thunderbird for $50. Shortly after, I was goosegazing at something, got too close to the car which was stopping in front of me, threw on the brakes and slid into him Learned two lessons that day.

"N8N" writes in article dated 8 Dec 2005 07:53:40

-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.

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

Since you appear to be replying to me, Huw, I'm well aware of the difference.

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 (More Off Road album links at bottom of the view page)

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.

I have not seen fours with harmonic balancers, only dynamic ones. I haven't looked that hard I must admit.

Huw

I have had several of these damned things fail over the years and there was never any obvious sign apart from throwing belts.

Huw

I believe so. Today, I ran the motor with the belt off. There are no signs of wobble. I was tempted to measure the crank pulley with a dial indicator and check the pulleys/idlers plane-parallel to each other but it looks tough. All the other pulley spin without effort. The tensioner is very nice and tight. Everything looks nice and clean.

I never buy belts from the same retailer once they fail. For the sake of documentation, I'd snap a photo of the belts, you could see it here.

Picture A is a beltfrom alloembmwparts.com, AKA thepartsbin.com, which I had beenfooled by their oem name. This belt shows signs of cracking in acouple weeks, which eventually self destructs. Picture B (not high-resolution image) is a pretty good belt, no signs of cracking evenafter a year, except for a section missing. Good retailer, in fact Igot many aftermarket rubber parts from pretty satisfied.

Poorly worded, I'll admit. I'd *guess* some ultra high revving ones might well have.