We've had lots of discussion on the life of toothed timing belts but nothing, so far as I know, on poly-vee belts. The engines I was usually involved with had the old fashioned vee belts, either single or in matched pairs, and I know little about poly-vees.
The poly-vee belt on my 1992 BMW 525i drives the water pump, alternator and steering/suspension pump (no air-con) through a tortuous run with the help of a couple of idler pulleys, one being a spring-loaded tensioner. I assume that the 'tortuous run' is necessary to get a good wrap-round of the belt on the pulleys on this fast-accelerating engine.
I would welcome opinions on the expected life of this type of belt and the signs of deterioration to watch out for. Also, do they break or just stretch and slip when they get old?
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I've seen a few of these belts with small stones embedded in them. On a couple of them the stone had been forced through the belt. I guess that wide, exposed belts are more of a problem.
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These belts seem to last very well even when badly deteriorated they still work. Things to look for are cracks across the polyvees and glazing of the back face. In my experience they last well over 30k. Most manufacturers fit a sprung tensioner but if your car has a rigid tensioner it will need checking at each service and possibly retensioning once or twice.
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I'd second that Andrew.
These belts do indeed carry a huge load, think about what they are driving, esp with a/c
Auto tensioners make our lives easier.
Most belts last 60K plus
MG-Rover Questions? Click on www.mg-rover.org
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MB belts last well up to 100k providing no FOD damage(Foreign object) & no oil gets onto them(terminal if sustained). Oil contamination can also make them noisy.
Simon T.
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These belts seem very reliable. I'd give them a life of 50k+. Mostly they get noisy rather than fail, or routinely get changed because of the rib sections breaking up.
Funnily enough I've seen that same "puncture" damage on timing belts.
Tensioners are quite critical on the aux drive belts as they run tight. Bearings will wear on these and that can make the whole thing pretty noisy with an old belt as well.
The mulit-rib drive belt is worn on my Xantia and it chirrups away sounding like something much more serious in the engine.
David W
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Thanks to all for your comments.
There is nothing in the service records to show a replacement belt on my car. It looks as though it might be the original, at 115000 miles, but I can't see any signs of imminent failure. There is some play in the idler bearings and these are slightly noisy when spun but not when the belt is on. The tension applied by the spring-loaded tensioner seems incredibly high!
Having taken your advice, I think I'll change the belt and bearings at some convenient point in the next few months but it doesn't look as though I need to panic over this.
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Dizzy
Polyvee belts seem very reliable. The belt on my Vectra was the original at nearly 80k when I sold the car. It still looked fine, but if I'd kept the car I'd have had a new belt fitted at the 80k service when the timing belt was done.
Regards
John S
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I detest poly-vee belts almost as much as timing belts. The reason is that in my honest opinion both are unreliable and both can fail without warning. My present car is a Rover 800 Di (no timing belt on these and they have self adjusting tappets!) Unfortunately the poly-vee and the A127-72 alternator are the cars twin Achilees heels. VM used to claim "no belt tensioning for 100,000 miles". Unfortunately the diodes in the alternators aren't up to the job of running 4 bulb headlights plus everything else and a diode failure every two or three years can be expected. (curiously the petrol Rover 800s had 100 amp alternators) Over the years I've got fairly good at rebuilding alternators and a new diode assembly won't break the bank. The 6203-2RS alternator front bearing is the weakest and most high revving bearing in the whole serpentine thingy but as Chinese bearings are so cheap one can afford to fit a fresh one at the same time as the diodes. A good tip is to use main beam sparingly and the same goes for the heated tailgate glass, although eventually it is hoped to fit a 115 amp Bosch alternator recycled from a Jaguar XJ6.
As to the poly-vee, I have had numerous belts on numerous cars shred. The trigger for the failure seems to be large steering commands. One belt failed about a quarter of a mile after a three point turn. If one has soft tyres this will aggravate the problem as the front axle load is approx 1 ton. I always carry a spare belt although these are difficult to fit at the roadside if one still has the infernal spring loaded tensioner. Finally I'd just like to say that Gates belts seem to be more durable than most types (one "brand X" - can't mention the name because of libel laws - only lasted a couple of months before all the string flew out of the back. That's not wear its tensile failure)
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I have noticed the double sided serpentine belts,e.g.Galxy/Sharan,tend to develop small cracks in the ridges quite quickly.The poly v on my Sierra only runs an alternator and lasts for years.
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