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My drive (serpentine) belt was recently chewed down to about half the width and I had to replace it.

Which brings the question: if the automotive industry has been gradually replacing timing belts with chains (my Tacoma has a chain and the model just a couple of years older had a belt), why not use a chain also for accessory driving purposes and replace pulleys with sprockets on the alternator, AC pump etc.?

DucatiKiller
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amphibient
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    Noise and cost. – Move More Comments Link To Top Jun 22 '15 at 18:48
  • so is a timing chain more noisy than a timing belt ? – amphibient Jun 22 '15 at 18:51
  • If something seized (AC compressor, alternator), it would destroy the chain. Belts allow for more flexibility. Chains need to be lubricated. – rpmerf Jun 22 '15 at 18:52
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    Yes, that was why the change was from Chain to Belt, Chains have been used long before belts were. Belts are quieter and cheaper. – Move More Comments Link To Top Jun 22 '15 at 18:53
  • but the evolution of the timing aparatus seems to be from a belt to a chain – amphibient Jun 22 '15 at 19:04
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    @Movemorecommentslinktotop - Make your comment an answer, because that is exactly why and you know it's the right answer. – Pᴀᴜʟsᴛᴇʀ2 Jun 22 '15 at 20:42
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    ^^ agree with @Paulster2 – amphibient Jun 22 '15 at 20:42
  • @rpmerf - I had a Suburban with 350-V8 in it. The alternator seized with a serpentine belt on it and stopped the engine dead. Replaced with new alternator using same belt: engine fired right up, no issues whatsoever. Chains do need to be lubed, though. – Pᴀᴜʟsᴛᴇʀ2 Jun 22 '15 at 20:44
  • The reasons behind the switch from timing chains to belts was A) cost - belts are cheaper for the car companies, B) increased repair revenue to replace those gddmn belts, and C) planned obsolescence - sooner or later someone fails to replace the belt on time, and then it's bye-bye engine. It used to be that cars were designed to fall apart after a few years, but customers grew tired of that, so now the engines are designed to fail after a few years - AND because it's caused by a failure to perform required maintenance it's "the customer's fault". Woot! – Bob Jarvis - Слава Україні Jun 23 '15 at 11:18
  • one other thing not mentioned yet -- the main motivation for using a chain in the timing set it the first place is the need to precise synchronization, hence a chain or toothed belt. For the accessory drive a little slip doesn't hurt and so no motivation to use a chain. – agentp Dec 08 '17 at 21:11

2 Answers2

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Here are a few factors besides the ones already mentioned that don't work in the favor of chains:

  • chains need lubrication. Do we really want another grease/oil in the engine bay?
  • pulleys would have to be replaced with sprockets. If some debris finds its way in the engine bay and lodges itself in a sprocket you can look forward to broken teeth in case something goes awry
  • chains are not as flexible as belts. Wrapping one around 5/8 of a sprocket is going to be difficult, so the packaging of the engine auxiliaries will be less compact
  • giving chains tension ain't easy. The chain tensioners I am familiar with rely on hydraulic pressure to keep the timing chain ship-shape
  • chains will have a lot more rotational inertia compared to belts. That is undesirable
  • steel belts (or Kevlar equivalents) are a more suitable alternative to serpentine chains
Community
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Zaid
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Noise and Cost. It's really that simple.

Chains used to be the most common device used for connecting the timing gears. Somewhere across the way someone told the consumer that cars shouldn't make noise and so the cheaper and less reliable belt was used by the manufactures. They did the same with direct drive (gear to gear) when they went to a fiber gear that also failed much sooner than the metal gears but were less noisy.

Move More Comments Link To Top
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  • I massively disagree with 'the less reliable belt' I have never seen a timing belt failure before its recommend life but I have seen dozens and heard of thousands of chain failures way premature of the manufactures recommended life. BMW & Ford diesel, PSA & Opel petrol all have issues with chains either failing or stretching – Newbie Noob Dec 09 '17 at 19:31
  • @TerryGould maybe I should have said less durable. Chains last the life of the engine, while some belts are changed as early as 60,000 miles – Move More Comments Link To Top Jan 24 '18 at 23:47