There's a great series of talks on youtube by Mike Mullane called the Normalisation of Deviance. https://www.youtube.com/watch?v=Ljzj9Msli5o I can see some parallels here - the belt service interval has been set by someone who has more data than anyone else. However, people start to deviate from this recommendation and nothing bad happens so it becomes acceptable. Until it isn't...
Thanks. I have to agree with you, based only on your experience. If you have not seen or heard of this cause, it is out of bounds. The diagnosis is just an old belief that had not been analyzed.
Well, it is certainly possible to break a belt due to an over rev. Downshifting from 6 to 5, but hit 3. Engine over revs, valves float, hit pistons, bend, jam. Cam can not rotate freely. Belt breaks. Tear down the engine and find broken belt with bent valves. Which happen first?
Sure, I suppose. Just because it has never once happened since Gilmer belts have been in use is no reason it can't happen now. Get real.
An independent service tech stated "most" belts break upon start up. The snap of the starter motor leads to failure under tension. Regarding downshifts, to be precise, I would assume it would be the rapid release of the clutch, i.e. dumping the clutch on a high rev downshift, not the actual shifting. High rev downshifts by a professional driver would not be done in this fashion. It's not the high RPM, it would be the rapid decrease in RPM upon clutch dumping. To rifledriver's point, the belts are not the culprit a lot of the time.
Yes, but I was making a theoretical assumption about how an IMPROPER downshift from high rpm could impart rapid increased tension on a belt and possibly lead to failure. Just like prior poster theoretically mentioned that over rev could float a valve and jam the valve train and then lead to belt failure. I'm not claiming facts or claim to have answers, just questions.
Neither ever happens. Your other comment. I have seen and repaired may belt failures. I worked at or was shop foreman at two of the countries largest dealer service departments. I have not seen a single belt failure at start up.
According to your previous posts a belt doesn't fail due to high RPM alone (agree), you haven't seen one fail upon start up and it doesn't fail upon improper down shift that would rapidly load the belt. Assuming that the pulleys, tensioners and guards are ok, what, in your opinion would precipitate a belt failure? I ask because I truly question that the belts themselves are part of the root cause of the problem. From a materials stand point, the primary factor would be either excessive rapid load exceeding the tensile strength of the material (rare) or repetitive ongoing loading under extreme condition from heat or contamination. In the real world it is likely a combination of both? And then add in the other non belt related causes and suddenly it is "multifactorial"? Hence the recommendation to change em every three years.
Au contraire. As I posted before, saying that an over rev can not kill a belt based on the scenario I posted is just nonsense. It's a chicken-egg thing. No amount if diagnosis after the fact would reveal the order in which things happen. With regard to belt failing on start up, I have personal experience with such a failure. Granted, not on a Ferrari but a Honda. In this case the car was driven form New Hampshire to East Hartford CT where is stopped for gas. Upon trying to restart the car, it would crank but not fire (89 Honda is not an interference e engine). Had it towed home and dug into it and found the drive pulley turning freely in the belt. All the belt cogs which were in contact with the drive pulley were sheared and remained embedded on the pulley. Plain and simple, the belt failed upon the attempted restart. However, the underlying cause of this failure was a leaking crank seal which had, over time, saturated the belt in oil, weakening its structure. Upon removal, belt cogs could be pealed from the belt with your fingernail. So, just because you haven't seen it doesn't mean it doesn't happen. Dismissing that things happen because you haven't experienced it just demonstrates a closed mind, not experience or expertise.
Correct. In cold climates this has been a huge issue in the past and cost manufacturers a huge amount of money. The belt when cold assumes a "set" and then the shock of startup and low flexibility of the cold belt can cause jumped teeth or breakage.
WOW interesting.........have any manufacturers issued warnings regarding the minimum temperature allowable for cold start?
No, they fixed the problem by changing belt composition, tension spec, changing service intervals, and later when they became available switching to the large rounded tooth belts. The very cold issue is also concerned with simple expansion/contraction of the engine which affects belt tension. Note: This information came from someone called Tony Rudd, in person, when he was alive. Wiki will confirm his credentials.
I don't care to argue about history so I will accept you statement. But you also state that the cold weather starting issue has been corrected. So it's not the issue, and it doesn't support the original unqualified statement that belts fail most commonly at start up. But, for a moment, let's accept that belts most commonly fail at start up. The problem is, even if true, it sheds no light on why they failed: age, mileage, contamination, excessive wear from improper installation, deterioration/weakness resulting from failure of a related component. All it says is that the application of starting torque was the straw that broke the camel's back. But if the starting torque was really the problem then wouldn't the applicable spec be how many starts the engine has seen rather than time and/or mileage? After all, the manufactures know that their cars will be sold to people may accumulate mileage at the rate of 10 or fewer miles per start and others who may accumulate mileage at a rate of 50 or more miles per start. In 50,000 miles that's like 5000 starts for one and 1000 for the other. Big difference in the number of starts. So, while the belt may commonly break at start up, it would appear that the act of starting is not the underlying cause.
I must be the one in a million that was (and still is) lucky enough to have avoided this huge disaster. I will either have to sell my Ferrari or move to a warmer climate before my luck runs out.
I would think it does support that statement. Its pretty obvious that this statement does not mean that people should be concerned about starting when very cold but it does mean that the belt is at its most vulnerable at this time owing to various factors, if some other issue is present such as incorrect tension, wear, belt deterioration etc. It was one of the issues the industry experienced in the switch from chains to belts and had to address, but the underlying evidence is that the belt might be at its most vulnerable at time of a very cold start. Note "The Industry" means generically. No evidence that Ferrari suffered from this issue although the belts are a standard type so seems generic factors would be applicable. The industry has still been making mistakes recently with timing belts, a recent BMW engine is known for belt failures. So that indicates a failure to understand and interpret anecdotal evidence correctly. The problem with discussing engineering subjects on a non-engineering forum. I will go back to F1technical.
"The only US (and common gray-market) engines that BMW ever used a timing belt on were the M20 6-cylinder of the late ’70s, 80s and early ’90s (used in the E21 and E30 3-series models, and the E28 and E34 5-series models (320/6, 323i, 325e, 325es, 325i, 325is, 325ic, 325xi, 528e, 525i) and the M21 diesel used in the US 524td (and various Euro models) of the ’80s. All other US model BMW engines have used timing chains." Perhaps you might point to which recent BMW engine you are referring to. By recent I would expect something at least in this century, hopefully within the last 5 years. I'm not aware of any. Image Unavailable, Please Login
BMW sounds like the N47 issue, which is chain, but timing all the same I Thought Gates provided a pretty nice lay explanation, their 9 reasons. I don't see that the '9' are exclusive. I 'assumed' the timing intervals are based on CBA by a company (and the belt MFR). I don't imagine it means you can drive how you like (including the environment) for X years regardless; rather it gives a framework for car management, e.g. inspection regimes and inter-related parts/servicing. Psychologically people will agree and do what the MFR says, or disagree and be cautious, or disagree and be less cautious, or disagree but for other reasons do as instructed. Accepting that manufactures 'learn', it unlikely that intervals will be on the cusp of failure, and will also be dependent on wider maintenance being met. As the sample of evidence is so small and the variable factors so wide, scientifically 'solving' this issue is unlikely in the near term.... But the debate does allow people to reinforce their position and sometimes change behaviours. So I am grateful for the debate. Anecdotally, one could imagine many Ferrari owners store their cars in heated garages, living in sunny climes.... perhaps if sunny and Magnum had lived in Alaska they'd have just had to suffer 911s, or Maranello would have finally sorted the argument for us... Personally I am grateful for exposure to all the differing views. Sent from my iPhone using Tapatalk
V late PS.... my better half reminded me of when we nearly bought a used 159 sport wagon a couple of years ago with 60k on its belt. Less than a decade since Alfa revised their (UK) belt changes down from 72k to 36k (159 at least), but not spotted by MDealer who had done all subsequent servicing. Owner wasn't interested in discounting sale price and claimed a FUll ARSH regardless so walked away. I'm sure it's not just the Italian MFRs getting it wrong though.... Sent from my iPhone using Tapatalk
I actually happened to be an engineer, and there is no failure of understanding or misinterpreting anything you've posted. Funny you should point this out. There is no "engineering forum" on here. This is the Technical section; that's as close to "engineering" as possible with respect to what FChat has to offer. And I will tell you what the real problem is, it's making assumptions (about what caused a belt failure and about what people do and don't understand).
Last sunday there whas a program on Globo Brasil Auto Esporte 12/03/2017 about belts falsifications. They last not longer then 16.000 km and about 30 % of all sold belts are falsificicated...in Bresil. Something to remind when buying belts. https://youtu.be/wr9mOhUyZ1A Guido
Ah, Brian. I always enjoy arguing with you. I know it's a no win situation, but it beats sitting here in CT waiting for 18" of snow to hit us. But I agree with the above quote. I clearly stated contamination was the underlying cause. The rest, you have your opinion. I, and jebones, have Newton.
You don't have that either. In a spin motors quite commonly go from maximum RPM to backwards much more quickly and violently than any stress in your dreamed up scenario and what do we see failing in those? Chain drive systems. Not belts. They survive. You guys can live in fantasy land all you like.
