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General Automotive General automotive discussion. This is intended to be a discussion about other not VW and Diesel cars you may have or interested in.

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Old May 28th, 2003, 09:41   #1
MrMetal
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Join Date: Apr 2002
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Default Why timing belts?

I'm trying to figure out why our TDIs have timing belts and not timing chains. What are the pros/cons of each?

Just eager to learn
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Old May 28th, 2003, 09:47   #2
BawlsyTDI
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Fuel Economy: 54.5/49/42
Default Why timing belts?

chain's tend to be noisy. Though with diesel clatter, who know's why the TDi doesn't have a chain. It sure would make life easier...
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Old May 28th, 2003, 10:33   #3
tomo366
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Location: Kensington, Maryland USA
Fuel Economy: Old Passat 40 Mercedes 20
Default Why timing belts?

TB's are much cheaper in the Manufacturing process.
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Old May 28th, 2003, 10:35   #4
trouter
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Default Why timing belts?

Belts are lighter (less engine load on acceleration ------ and ------- cheaper
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Old May 28th, 2003, 13:16   #5
RiceEater
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Default Why timing belts?

Thousands and thousands of years ago Jaguar (I think ~1950?)was among the first overhead camshaft pioneers. This got rid of the pushrods, rocker arms, quadruple valve springs, etc. Unfortunately this ran on something a little smaller, maybe larger, but I forget>>I remember, than a bicycle chain. If the chain held together it was sweet and smooth. If it didn't, it was kinda like me and my severe Alzheimer's. Anyway, ChemE's got better and better and so did the belts. This offered cheap dependable belts that were quiet versus more expensive noisy chains. Gear drive would mean huge expense. There are other options available to engineers but I forget.
The vast majority out there at the time was pushrod V-8s with valve trains running on nylon gear teeth and short multilink chains. To offer a OHC like the Jag or better would mean more noise or more valve train friction. During the 70's Bear you could only get 5 gallons and only if your license plate ended in an odd number. This environment established the reinforced rubber belt as the small OHC tradition.
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Old May 28th, 2003, 15:39   #6
MOGolf
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Default Why timing belts?

Chains require constant lubrication. This makes the engine more expensive to manufacture. That would push the price of the car above what the targeted market is willing to pay.
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Old May 28th, 2003, 17:45   #7
tdibugman
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Default Why timing belts?

Quote:
Chains require constant lubrication. This makes the engine more expensive to manufacture. That would push the price of the car above what the targeted market is willing to pay.
While I understand the thinking, it makes no sense.
We all paid MORE money for a TDI to begin with; if it costs them 100 bucks more for a chain, charge me 300 more: if it means I don't have to change a belt, the better off I am.

OTOH, I still have the Bug, but have bought 2 new Saabs: a 9-5 and
9-3SS. Both have, to my delight, surprise and joy, proper timing chains, to never be replaced or messed with.
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Old May 28th, 2003, 17:52   #8
Frank M
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Default Why timing belts?

Chains rob horse power
Belts don't (not as much)

As far as costs go, a Ferrari Testarossa $200,000 has a timing belt that has to be replaced every 15,000 miles or 3 years.
Engine has to be removed and the average cost for the job is $5-6000

You would think if money were no object as in the above example they would put a chain in. However power is the more important. All 475 HP
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Old May 28th, 2003, 20:01   #9
tdibugman
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Default Why timing belts?

I still don't buy that reasoning.

A family friend happens to be an F355 F1 driver. His t-belt gets changed every 30K miles - almost the 40K my New Beetle requires (he has 135K on it now). Its a 3500 dollar operation. But, I would also suggest that to this guy, 3500 bucks is probably what he lost in AC last weekend. So, form an economic standpoint, if you can swing the payment, you can swing the maintenance. BTW - for 3500, they do A LOT of other service while its in. (12 qts Mobil 1, pads/rotors, etc)

What TDI owners are forced to spend (most of them anyway) is downright ridiculous based on the cost of the car. My dealer quotes about 700 dollars for a change. The last time I checked, VW is still a peoples car, and is driven by folks who work hard for their money and to pay off their car. the least VW could do is put in a damn chain!!!
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Old May 28th, 2003, 20:51   #10
banzai
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Default Why timing belts?

My mother now drives a 1994 Nissan Sentra- the little one.

It has a twin-cam chain driven valvetrain. Not a big deal or a selling point to them but something I noticed.

My 1970 Toyota truck had a nice OHC (18R-U) driven by chain, as does my brother's 1972 MBz 220
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Old May 29th, 2003, 10:38   #11
nortones2
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Default Why timing belts?

Toyota Yaris (Echo in some markets?) diesel 1.4, petrol Yaris's, Honda 2.0, Ford (some) all have chain cam drives. Can't cost too much! We on the other hand have (but not for much longer) a VW 1.6 gas engine Vento (Jetta) which mangled its valves when the belt broke at 72k. A chain cam car will soon arrive
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Old May 29th, 2003, 10:58   #12
RiceEater
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Default Why timing belts?

There are a huge number of incompetent mechanics out there breaking timing chains. Timing chains do need to be replaced, albeit at a lesser frequency than belts. A lot of mechanics would check ignition timing but failed to check the spark advance mechanism throughout its rpm range. A characteristic of a timing chain well beyond its time is timing fluctuations as rpms decrease. There is an established history of pushrod engines mysteriously failing shortly after being tuned by a "good mechanic." Anyway, just wanted to remind everyone that the timing chain does not eliminate but only extends the change interval.
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Old May 29th, 2003, 12:12   #13
GoFaster
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Default Why timing belts?

Timing chains usually (note: USUALLY!!!) don't fail catastrophically, at least not on OHC engines that have long timing chains with plastic guides and spring-loaded tensioners (this is the way practically every motorcycle engine is, and it's the way a Toyota 22R or 2TZ is, and it's the way most other OHC auto engines that have timing chains are). Usually if something goes wrong, they start making a helluva racket which prompts the owner to investigate. Timing belts just go bang, bye-bye engine ...

I had the timing chain done on my '94 Kawasaki at 88,000 km because it was making a racket. I never touched the timing chain in either my Toyota 22R or the 2TZ.

None of these chains have any lubrication specifically for them. They run in the lubricated portion of the engine and get splash lubrication from everything else - there's no oil feed explicitly for the timing chain - lubrication is not a big deal, it just has to be on the oily side of the engine covers instead of the dry side.

I don't buy the power-loss thing. Motorcycle engine manufacturers work very hard to get maximum power output and everyone except Ducati uses chains!

I'd rather have a chain in there ... in fact, with the TDI's lack of need for high revs, I'd be fine with pushrods and a gear driven cam low on the side of the block ... a Cummins is like this ...
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Old May 29th, 2003, 12:34   #14
RiceEater
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Default Why timing belts?

GoFaster,
All good points. I just want to say that in this environment you would be asked about the noise coming from your OHC chain. I contend that most of your workarounds would involve more friction which leads to some power loss. But of course this is not an engineering forum though a few members are so open minded and eager to learn.
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Old May 29th, 2003, 13:56   #15
nortones2
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Default Why timing belts?

The missing word is "greatly" Belt drives have no lube, and maybe they don't need it- but they do fail early, and require changing at say 40k to 60 k. What is the life of a single chain drive - 150,000 at a guess? Guess which method cuts out the incompetent meddler until the second or third owner? BTW Jags used to use a duplex drive for their old inline 6. I suspect that lasted until the tin-worm had done their worst.
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