why rubber timing belts??

I would imagine so the dealerships can capitalize on it through a higher cost of maintenance to the consumer

 

Timing chains add too much weight to the car but don't lighten the owners wallets enough to satisfy the Ferrari parts and service department.

 

Supposedly it was initially done to save the weight and drag on the engine that a chain would produce. I'm not sure but I think the rubber belt is quiter also.
BT

 

Maybe rotational inertia as well as the weight? There was also the issue of noise. Ironically, when I first heard about them in the old Pontiac overhead cam six, the claim was that they would last longer than a metal timing chain and gears.

Don't know if anybody remembers this, but the older Porsche 911 cars used to have a lot of trouble with the timing chain tensioners - you had to replace them pretty often (I was told at about 25 to 30K miles). A failure of one was just about as big a disaster as a broken timing belt.

 

how come you get all the respect, when i got shamed on this question a couple of months back?

 

Rubber belts were never thought to be a weak link when they first came out. Race cars used them to lower rotational mass so Ferrari used them in the road cars as well. Only later did they realize they were a weak link. I can't say why they went back to chains, but I imagine they are superior to the old belts in some way BESIDES longevity.

I can't speak for Porsche, but my 1972 Lotus has a timing chain and it's still going strong. In our community, broken timing chains are virtually unheard of.

Ken

 

I was told the older Porsche chains had a bad tendency to "whip" around because they were so long...the tensioners apparantly had a lot of work to do absorbing the shocks as well as just keeping it all tight. They were driven by oil pressure, IIRC, not really spring loaded. I was also told that this is not a factor on the 993 - source RUF Porsche when they did my top overhaul.

My point was that maybe the belt system was not quite so evil as we have come to believe - I have heard few issues with other cars that use them; Honda, maybe - but the replacement interval must be 4 times what Ferrari expects of us.

 

Belts are cheaper and quieter. Ferrari chains provided they are properly tensioned are basically trouble free

 

Ken is correct. The rubber belts offer more performance, less weight.

FYI - Chains break, too, guys! I bought a Benz dirst cheap thanks to a snapped chain. They just can't handle the high RPMs without the tensioners wearing & the chain chattering/snapping.

I have no idea how the new generation of chains can rev so high. It would be interesting to see a tech article on this topic.

 

Part of the reason the belts have such a short life cycle in a Ferrari's is LACK of use. The longer you leave a rubber belt pulled over a cog it will create a memory thus becoming weak in that spot. There are plenty of cars (many makes)on the road with over 100,000 miles on the same belt. As far as variators and tensioners in a Ferrari that may be a weak point (they have undergone several updates in the 360)
To answer you original question Rubber belts are quieter, cheaper to make and offer less parasitic loss.

 

Don't look at me. I'm strongly in favor of equal shaming.

 

Don't Lambo's use chains ? you never hear any compalints about timing chain probs from those guys.
My old 70' Corvette had a chain for 120k miles before I sold it, never had a problem or made any noticable noise. (didn't rev to 7700rpm though- 6k max)
I wish someone would come up with a chain to replace the belt on our cars.

 

whats the service costs on the 430 with chains vs the 360 with belts. does f still recommend 3 yr chain replacement? is it still engine out procedure?

 

I don't believe it is a engine out on a 360. Just us lucky guys with tr's 348's and 355 oh an Mondial t's

 

yea, you would be.




_________________________________
i'll do it my way...

 

There is no service recommendation on the F430 chain and it is not an engine out to change the belts in the 360.

 

It's just Ferrari recommending rediculously short replacement cycles. Most imports use chains, and my 500 HP Evo had 60K on the clock when I changed the belt. The only reason I changed it was because the motor was already apart, otherwise I'd probably never change it.

From what I've read, belts stretch less than chains too.

 

I broke a chain in my '69 Pontiac V8 400 CI. Actually the metal links were fine, it was some nylon spacers that broke (IIRC) causing the chain to skip. Fortunately there was no interference...

 

Right, Ken, just leaking water pumps and severe fiberglass stress cracks! (Actually, you're a Europa owner, so you have different issues than those I've dealt with on the Elan.)

Porsche 911 went to a new tensioner in the 1980s, and the engine that went into the '70 911T I had four or five years back had the later tensioners installed. It is true the original tensioner design could fail, resulting in the proverbial "big bang".

There's always a reason for every automaker's part decision. It comes down to looking at the priorities of cost, reliability, performance, NVH (noise, vibration and harshness), ease of service...and deciding what ratio of each area makes sense given the application and price of the vehicle. In the case of V8 Ferraris, belts simply made sense, whereas the company felt the V12 would do better with chains.

 

My experience with cambelts are on my HONDA Goldwing motorcycle and first seeing them on late-60's, Fiat 124 Spiders and Coupes, which were powered by a twin-cam 4 cylinder engine. Harley-Davidson's have run them as final drives for 25 yrs. or more.

Some general statements that apply to both are, that oil will destroy them in short order, and keep them in proper adjustment, and their durability will be fine. Failure of adjusters and seals, seem to be their downfall. If designed and executed for their task correctly, you will only change them once during the life-time of your engine, and TIME, is the big factor, in their durability.

Ciao...Paolo

 

For the record, TC water pumps will last longer than 10k miles when done right on the TC engine which we share. Few people are up to the task which contributes to their bad reputation. My water pump died at 49k miles which isn't bad. As this is an engine out replacement on the Europa (okay, the truely skilled can do it engine in but it's only an hour or so to pull a TC engine on a Europa so why suffer?) I paid the big bucks for a new front cover and an after market cassette water pump, so that it can now be replaced in 15 minutes engine in. Well, maybe 30. So if I ever sell my car, the next owner need not worry. The deal with Europas is that they work great within specs but there's NO margin for error so if the belt is a little too tight the WP bearing is shot fast; too loose and the cooling is suspect. I've always said a 308 would be reliable compared to a Europa but only if you don't fix the Europa correctly. My car now is actually reliable but it took a few years.

As for stress cracks, Europa fiberglass seems as thin as aluminum foil! Not sure about the Elan. You get them, but with mostly original paint my car has a pleasing patina and they're not bad. I've not got a repaint on my list (yet). If I raced it in autocross like so many Europa owners still do, it would be a different story!! Racing kills the paint/body in a hurry on a Europa.

Ken

 

The reason they ran belts has more to do with the principles of power loss, inertia and acceleration than anything else.

 

Technology has come a long way and that applies towards timing belts too. With that in mind one would think that the belt service intervals could be extended dependant upon the materials used for manufacturing...

"Section 6. Hydrogenated Nitrile Rubber-HNBR, loaded with chopped Kevlar fiber and PBDMA (Maleated low molecular weight polybutadienes)

HNBR has an excellent combination of properties, including high thermo-stability, good oil and solvent resistance, and other useful properties for the production of belts to be used in demanding environments. The addition of short fibers into HNBR formulations provides dimensional stability during manufacturing process and prevents size distortion during usage. Short fibers also give high modulus at low elongation, increased hardness, and increased creep resistance. All of these properties are very desirable for the production of timing belts (for example). The joint application of aramid fiber and PBDMA, however, gives even stronger improvement in HNBR properties (Table 10). Figures 12 clearly illustrates the great increase of the modulus at low 10% elongations. For formulations with both PBDMA and fiber, these modulus strengths were increased up to 1.7 times relative to formulations with just fiber. The coefficient of orientation in the presence of PBDMA was increased up to 70%."

http://www.sartomer.com/TechLit/5713.pdf