Why did Ferrari use belts instead of chains?

I learned to drive on a 1982 Nissan Sentra that was two of the three. My Ferrari only meets one of the three, and it's the one the Nissan didn't have. I'm sure you can guess which one!

 

FYI, Ferrari went to cam belts in the 70s with the Dino, Boxer and 308

 

LOL, thats about where I am at the moment: cheap and reliable.

 

Belts or chains as previously discussed have their advantages and disadvantages. The belts were chosen for their quietness and flexibility while chains have longer life expectancy. The weaknesses in belts were the materials used to make belts eventually hardens and break or additionally the tensioning system also weakens and fails. The chains have 3 possible areas of weakness-the links (stretch over time), the rails on which they ride and are guided were made of plastic (which also can wear out and become brittle over time), and lastly the tensioner system as well.

Porsche decided to go with gear drive (for the 911 engine placed into service for the Mooney aircraft) because of the FAA ruling governing aircraft engines safety and reliability. For their street version and racing 911 variant cars they chose chain cam drive with the proviso of using the finest and strongest chain available at the time. They have been quite successful using their chain drive as evident from those engines being quite reliable. The fact that they went through 5 iterations of the tensioners over the last 40 years is just perfecting their design. The 911 engine has a well deserved reputation of reliability given the thousands of endurance race victories achieved under long distance racing. Their newer cars 944, 928- which uses the belt are not quite as reliable and the reason for belts were noise and comfort being more desirable for their owners than 911 buyers and owners.

The Boxsters and Caymans have a service hatch for changing the major accessory belt behind the driver that has to be removed and the service of the engine can be done without engine removal. I believe Porsche's Cayman and Boxster' s service hatch is the inspiration for Ferrari to design the 360 and 430 to have their belt location accessible the same way (by having a removable panel in the front of the engine).

Timing belts have gotten better over their development and use. The older designs (rubberized over fabric skeleton ribs) needed changing at 60,000 miles or 5 years for Honda which now have been changed to Kevlar/rubber or synthetic polymers with 110,000 mile use longevity. Kevlar belts are literally bullet-proof. However, whether Ferrari does development and research on their engines components which typically don't see much extended use is another topic of discussion.

 

Beg to disagree on a couple of Porsche points - first being: the 911 cam drive design. The older cars were notorious for tensioner failure. Or, at least tensioner got loose, let the chains whip around and they get loose from the cam, which meant instant martyrdom for the engine. Tensioners needed changed (at great cost for the day) about as often as the belts on a TR. Only with the 993 was this fully resolved, along with the myriad oil leaks. You have to admire Porsche for sticking with this design for so many years and stubbornly resolving all the problems over time.

Second: Go back and have another look at the 928. The first cars had SOHC, with a chain, IIRC. Later when they made the quad valve, with DOHC, a second very small chain picked up the drive and transferred it to the second added cam.

Again, IIRC, never actually took one apart - but that is what I saw in the cutaway drawings.

 

Mr. Woods,
I agree with you that the chain tensioner of the 911 design was not perfect from the get-go. But you also agree that instead of changing over to belts and trying other solutions, Porsche was to be admired for sticking it out with their original choice of chains and fixing the weakness in the tensioner. However, I stated clearly that the chain was never the weakness and there have been very few failures of the chain itself that lead to expensive repairs. Your desciption or clarification being that the tensioner was the cause of the expensive damage is redundant.

The original Porsche tensioner was known to be a problem area when left alone without regular service (if regular valve adjustments at 30K miles and opening up the timing chain covers for inspection and adjustment were not routinely adhered to). There was also a mechanical collar that one can add to the stem of the tensioner to act as a safety device that prevents the tensioner from failing which was a cheap fix as far as addressing this issue. The 1984 Carrera 911 engine has an oil pressure fed tensioner (version 3 or 4) which was pretty reliable (100000-200000 miles lifetime). The service requirements of the 911 flat 6 has been pretty much relagated to changing the oil and adjusting the valves with occassional head studs breaking over time and oil leaks from various seals that dry up and crack. Valve guides were prone to need repair in some batches of bad metallurgy and tightening emmissions smog regulations especially for the 1974-1977 years of 2.7L engines with the thermoreactors and air pump disasters.

the 928 engines never used chains (for the cam system) as far as I'm aware. There was a belt tensioner gauge special service tool for adjusting the timing belt tensioner when changing or servicing the timing belt in the 944 and 928 series engines. Any chains you saw in the cut-out diagrams are for the Varioram system which porsche used for changing the valve timing while the engine is running to optimise valve timing and torque output efficiencies.

 

Well, we are pretty much in agreement on the 911 issues, and as I said - I was just going on long-lost memory on the 928 engine. Turns out it WAS belts & not chains.

I think that the serious point of this thread is that we should put to bed the myth that somehow chains are good, gears are even better, and that belts are totally bad.

They all have their advantages and disadvantes, and it is really without purpose to armchair engineer something like a 12cyl Ferrari after the fact just because we don't like the maintenance schedule.

 

The Porsche aircraft engine was a terrible design. http://www.seqair.com/Other/PFM/PorschePFM.html

 

After the Mooney-Porsche failure, they only used it in blimps. That may in fact speak volumes about the reliability factor.

 

JCR and Mr. Woods,
Thanks for the interesting source posted on the failure of the Porsche aircraft engine (from the viewpoint of their competitor Lycoming). While I can accept the failure of the engine as designed for aviation use and its discontinuation because of its non-competitive nature (price vs. perceived value) the conclusions that you seem to present as to why it is a failure doesn't make sense from a logic standpoint. You seem to imply that applied to the question of the original thread posting here (belt vs chain drive or gear drive in engines) that because the porsche engine which uses gear drive or chain drive was a failure as an airplane engine that belt drive would have been the superior or more correct way of designing an engine for reliability sake.

The author of the article posted by JCR mentioned the problems of the application of the porsche engine (were mostly relagated to packageing the engine into the airframe) and said that there were very few interchangeable parts between the aircraft flat six engine and the 911 engine of the time (1984 911 Carrera engine). That is true not because you cannot take parts from the aircraft engine and bolt them directly onto the car engine (whose components, crankshaft, valves, gears, pistons, cylinders, oil pumps, dry sump , etc. are identical in dimension and metallurgy and application). The fact that the car parts are not certified by the FAA to be useable interchangeably with the aviation use engine is a matter of regulation and policy more than any reliability matters. The fact that there is designed 2 redundant ignition system for the 911 aircraft engine is again due to rules for airplane engines rather than reliability issues. The failure is a result of not wanting to invest any more research and development into a project that will not sell enough to recoup on investment. Also Mr. Schultz was let go because Porsche was reeling from the stock market crash of Oct.,1987 and Porsche's market contractions not because he sent the company's resources into different areas outside Porsche's expertise.

 

This is by far the most entertaining thread I’ve read in a long time.
Today I was bored and decided to read a thread with many posts, and this is the one.
Thank you all very much, most amusing and entertaining.

Ferrari used belts because it looks “racing” and it was the best thing at the time. lol.

Just 1 Q from me, why getting aggravated by someone starting a thread with a question?
Answer the freaking question without trashing people or calling them names or just don’t bother typing an answer and the thread with the “worn out” subject will die by itself.

I’ll bet $100 I’ll be called a name now. But who cares?

PS.
I love reading these worn out subjects, every now and then somebody comes up with something new. And that’s part of the point, isn’t it?
Have a nice evening ALL of you
DS.

 

And leave it at that.

It probably was not a bad aircraft engine at all, as a matter of fact. I will give you that.

However - there really was a problem with perceptions...(and again I am going back a number of years, but I was an active pilot and aircraft owner at the time.)

Here is my possibly tainted memory of the situation:

a) It was expensive. The "mass production because it came from a car" was really a myth...it came from a Porsche, not a "car".

b) They picked Mooney for the beta test bed. Mooney was not a bad airplane at all, but it too had a little bit of a P.R. problem in those days - financial & ownership issues; it was considered as a small and impractical airframe back when people really bought Skylanes rather than pretty little sporty planes.

c) It was unconventional. In many ways, an old Corvair engine would have been more like a Continental or Lycoming. Not only the gear drive, but there was the fact that it had to be geared to the prop and ran at over prop RPM. Also, and I think this may have been critical, they attempted a "power management lever" rather than a conventional throttle and constant speed prop control. General aviation has long been notorious for resisting innovation - (at least within the business owners who really fund GA activities). Sporty planes with control sticks, G harness & parachute wells, inverted systems, etc. are for the EAA and Oshkosh, Wyoming in their view.

d) It was a time of extreme stress in the GA market. Insurance issues, liability, V-Tail Bonanza paranoia, fuel cost, economy - things looked pretty bad for small single engine aircraft.

e) There are cynics who still say the FAA did not ever want it to happen (with help from the U.S. engine makers lobby) and made them jump through a lot of hoops.

So, no - I was not trashing the Porsche effort; the blimp thing was said in jest, of course. But, if I had just added the word "perceived" to the reliability comment, I don't think I would have been far off the mark.

It all has nothing to do with Ferrari & belts, of course - except to illustrate that there about as many things political as metal when you try to make a product nowadays.

James

 

How do we analyse the reason for a street auto engine design to use BOTH chains and belts. Hint: Designed by Yamaha.

Cheers
Warren

 

Now you had to go and bring that up at this late moment. You are not referring to the late lamented Ford SHO, I guess?

Rather than researching it today, I am still trying to get through the molten sodium recycling of lithium ion batteries.

 

I kept waiting for someone to notice that it is not Chains VS Belts, even for a given manufacturer or engine designer. So I tried to find my SHO manual in my "well organized" collection, but finally gave up for the moment.

I bet you didn't need the hint!

Cheers
Warren

 

Porsche engine cost more, and gave less in the way of performance. Simple issue: you didn't get anything for the extra money. Stupid idea, motor wasn't designed for aviation, and didn't work well in that arena.

Art