Timing Chain vs. Belt

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

 

cT = 1.0

 

Please clarify ...

 

Please excuse the duplicate postings as the first took forever to
appear ...

 

You've got it backwards. They're returning to chains after a few decades
with belts.

 

Seems like belts would be cheaper and easier to install, correct? I'm no
gearhead haha

 

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.

 

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

 

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.

 

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

 

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.

 

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.

 

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.

 

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".

 

....which is why there isn't a Honda manual within ten miles of a
dealership service desk.

 

Impossible - I think not...

http://www.wrljet.com/fordv8/images/64-indy-gears.jpg
http://www.southbayriders.com/forums/showthread.php?t=24346&page=1
http://www.southbayriders.com/forums/showthread.php?t=35358&p=492156
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

 

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.

 

<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!

 

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

 

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.