Timing Chain vs. Belt

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Why are so many cars going to a timing belt ? ...

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On 06/03/2011 10:05 AM, Steve Giannoni wrote:

cT = 1.0
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Please clarify ...

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Please excuse the duplicate postings as the first took forever to appear ...
On Fri, 03 Jun 2011 13:05:28 -0400, Steve Giannoni
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You've got it backwards. They're returning to chains after a few decades with belts.
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Tegger

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On 6/3/2011 6:01 PM, Tegger wrote:

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From what I've been told, no. Belts and chains involve similar production costs.
The change /to/ belts was driven primarily by two factors: 1) the switch from cam-in-block (OHV) to cam-in-head (OHC), and 2) emissions laws.
Japanese automakers tended to use regular link-chains instead of the inverted-tooth chains common on domestic OHV engines. OHC requires a very long chain. Long chains stretch more than short ones. A stretched chain changes valve timing (and sometimes ignition timing), which affects emissions. Belts do not stretch, so long belts work better in keeping an engine emissions-compliant than do long regular link-chains.
The switch /away from/ belts is driven primarily by the desire to get away from the lousy reputation belts have on account of the need to replace them frequently: owners HATE having to spend big bucks to replace belts, and hate even more being stranded when a belt breaks.
The new chains used by Honda and other Japanese makers are inverted-tooth chains. These are far more durable than the old-style chains.
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Tegger

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I would have thought that gears would be much more efficient, last longer, replacements would be primarily non-existent. Cost would be a bit more but the benefits should outweigh the costs.
DaveD
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Gears are heavy, noisy, and expensive. In the later years of gear-driven camshafts, it was common for the gear teeth to be either coated with such substances as silk, or to be made of nylon. These were attempts at quelling noise.
It's also just about impossible to control an overhead-cam engine with gears.
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Tegger

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On 06/04/2011 05:21 AM, Tegger wrote:

??? no harder than with a chain or belt. think about it.

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Impossible - I think not...
http://www.wrljet.com/fordv8/images/64-indy-gears.jpg
http://www.southbayriders.com/forums/showthread.php?t $346&page=1 http://www.southbayriders.com/forums/showthread.php?t5358&pI2156 http://www.avrosys.demon.co.uk/bomber/engines.htm
http://winfield.50megs.com/Engines/Gallivan.jpg
Maybe not a good idea, but certainly not impossible.
Ed
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On 06/06/2011 07:20 AM, C. E. White wrote:

read his post again ed - you missed the word "control". "control" does not mean "drive" per every "cite" you've given, it means "manage" for things like variable valve timing.
gear driven cams are no harder to control than belt or chain driven cams. it would make absolutely no difference for the honda v-tec or the toyota vvt systems for example. it'll be more expensive than the "variable chain slack" systems like porsche, but even "high end" manufacturers need to manage costs.
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jim beam wrote:

I can't speak for "modern" machinery but all of my ancient Studebakers have gears and failures are hardly ever an issue. So is variation due to wear.
My '64 truck had nearly 400K on it and the engine was tired but not from the gear point of view.
The gears in regular cars were steel for the crank and phenolic for the cam. The "R" series engines used an aluminum cam gear.
Noise was never an issue with any of 'em.
I suspect though that use of gears in modern stuff might increase manufacturing costs...
JT
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<snip links>
OK, I amend my statement to read, "just about impossible" at a mass-market, road-going-automotive budget, and with the usual consumer-market considerations as to noise, weight, and complexity.

Not a good idea at all for road-going consumer-grade automobiles. Just look at that motorcycle in one of your links: SEVEN gears! And that's NOT counting the ones for the actual crank and cams!
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Tegger

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On 06/04/2011 02:33 AM, Dave Dodson wrote:

you're presuming that's what the manufacturer perceives to be in their interests. particularly if you consider the detroit model of the 100k mile vehicle that is utterly done by 100,001 miles.
in reality, chains and belts are much simpler, cheaper, and adequately reliable for auto use. belts offer particular advantages.
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On 06/03/2011 06:25 PM, Tegger wrote:

indeed.
they don't hate getting their cars maintained - they hate getting gouged. a belt change for most vehicles doesn't take that long, especially for an experienced competent tech. but by the time the dealer has inflated the actual time taken, and has done unnecessary work like changing seals that aren't leaking [which a non-competent tech will frequently screw up], the price gets /way/ inflated.
there's even the issue of the coolant pump. honda oem pumps are very good and very reliable*. a change schedule is /not/ specified in the service manual. yet you'll never find a dealer that doesn't take the opportunity to change it, and overcharge you for it. "but you may as well do it while you're in there" is the argument. well, why not change the alternator when you're changing that belt too? why not the power steering pump? it's just something people have been conditioned to accept like 3000 mile oil changes.

* cheap non-oem pumps are not reliable. but those don't even last the life of the belt, so again, there's no logic in syncing the two there either. a good honda pump with quality coolant and with a correctly tensioned belt will last at least as long as the average starter motor, or alternator. change when necessary, not because of superstition.
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to be fair, if the alternator goes out three days after changing the TB, do you have to do all the TB labor just to have enough access to change the alternator?
A water pump WILL go out, even Honda OEM. And it's a cheap part to handle while you've already spent the time/labor to get to that point.
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On 06/04/2011 08:47 AM, Elmo P. Shagnasty wrote:

if you want to change the alternator on the 88-00 civic, you have to take a driveshaft out. technically, you could change the coolant pump without taking off the belt, just slacking off the tension.

it's "cheap", but frequently over priced - like 3x. the honda manual says "inspect", not "replace" or "inspect owner's wallet".
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...which is why there isn't a Honda manual within ten miles of a dealership service desk.
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Chains are more durable. But problems occur when there is a nylon gear, that is driving the chain. The teeth wear down to where the chain slips off. Maybe causing it to slam around the engine Causing significant damage. American, and Japanese cars both used them since the 80's. Because the nylon drive gear is quitter then a more effective metal gear.
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