New timing belts / valve adjustment interval? Miles vs Time

[Kev M]

Would you say that automotive interference motor timing belt failure is any less catastrophic?

Hell, I could buy a new Ducati for the price of some longblock automotive motor replacements.

I guess I'm playing devil's advocate here, but I'm mostly saying that Ducati replacement intervals are RIDICULOUSLY conservative for the average street bike.

[ungeheuer]

Would you say that automotive interference motor timing belt failure is any less catastrophic?

Depends.  How much does it cost to replace?  Can I do it at home myself?  Is it a rental car?

I guess I'm playing devil's advocate here, but I'm mostly saying that Ducati replacement intervals are RIDICULOUSLY conservative for the average street bike.

I'm mostly saying that the catastrophic damage resulting from finding out the point at which ridiculous ends... is something I'm prepared to approach conservatively  .

[He Man]

Herpes lasts for life.  What's your point?
 

AHAHAHAH!!!! Ive got a screen full of spit and water!!!!

I guess I'm playing devil's advocate here, but I'm mostly saying that Ducati replacement intervals are RIDICULOUSLY conservative for the average street bike.

Unless you have the math to prove it (or a copy of their design calcs) I wouldnt say something with such certainty. You dont know if they designed the belt with a safety factor design or a type of load resistance factored design (which uses probability of failure modes to apply a strength reduction factor). You dont know what kind of assumptions they used when they designed it, in fact the only thing you do know is that it hasnt broken on you.

[Howie]

Automotive timing belts do not run anywhere as tight a radius at the sprockets and generally don't run as high RPMS or changes in engine speed.  Nor are most automotive belts removed and re-tensioned (another stress) for valve adjustments They also do sometimes fail prematurely.  There has also been a slow move from belts back to chains.  

Condition of the rubber is, although the usual failure on a Ducati, not the only consideration.  The aramid fiber will, though not as quickly as steel, eventually fail, undetectable to the eye until too late.

[Howie]

<snip>

Unless you have the math to prove it (or a copy of their design calcs) I wouldnt say something with such certainty. You dont know if they designed the belt with a safety factor design or a type of load resistance factored design (which uses probability of failure modes to apply a strength reduction factor). You dont know what kind of assumptions they used when they designed it, in fact the only thing you do know is that it hasnt broken on you.

That and more.  My dad never changed brake fluid or transmission fluid in his cars and never had a problem.  Guess I should do the same?  Or maybe that is why I couldn't stop his Lincoln from 100 MPH?

[Kev M]

You're right, I don't have any hard and fast science to go on with regards to the particular belt composition, loads, etc.

I only have anecdotal evidence.

It seems to me that in this thread alone with have what, a half-dozen (I didn't go back and count) people who have DOUBLED the time requirement on their belts without a single report of a problem.

It seems that at least one report from a Ducati master-tech who advised the same.

Though not direct comparisons, the Harley final drive belt and the automotive timing belts certainly add some evidence that belts in these types of applications can have SIGNIFICANTLY longer shelf lives (with regards to not degrading too rapidly just from ambient exposure over time).

Certainly I would think the Harley drive belts have much higher loads on them, even considering what I think is a larger size belt.

I don't know that I'd consider the rpm differences that much between an automotive drive belt and Ducati, not unless we're talking a race environment. But of course, the difference in replacement intervals are just staggering, off the chart different. Perhaps radius is a bit tighter, but is it enough to make THAT big a difference?

I guess part of my attitude stems from watching maintenance intervals across the entire industry both be extended as materials and designs have improved, and also be ignored by the average consumer with only the most extreme examples usually resulting in a catastrophic failure. I realize that is a HUGE generalization, but it certainly suggests that manufacturers are purposely conservative with their recommendations (perhaps as much to counteract the public's tendency to stretch it out anyway as it is to protect their reputation by preventing problems).

Again, I'm not telling anyone what to do here. But the overwhelming evidence that I've sourced from multiple owners of Ducatis is that given reasonable/gentle usage, the OEM replacement interval of time alone seems uber-conservative.

No, I'm not about to use it till it breaks for a data point.

I AM trying to make sure that we at least hit the 7500 mile mark by the close of year 4 and we'll just go ahead and do the whole she-bang (belts and valves).

But I'm certainly not going to stay up late at night worrying that 3 year old belts are gonna go on my bike with only 5k miles on em.

[metroplex]

I asked Gates and they weren't adamant about any type of lifespan for the belts (probably to cover all their bases), but they did say the shelf life of timing belts is typically 6 years.

This is not saying that the OEM Ducati belts will last shorter or longer, but it seems like the same conservative estimate that some tire manufacturers used to use a few years ago, although many tire OEMs now indicate the shelf life is 10 years for tires.

[He Man]

You're right, I don't have any hard and fast science to go on with regards to the particular belt composition, loads, etc.

I only have anecdotal evidence.

It seems to me that in this thread alone with have what, a half-dozen (I didn't go back and count) people who have DOUBLED the time requirement on their belts without a single report of a problem.

It seems that at least one report from a Ducati master-tech who advised the same.

Though not direct comparisons, the Harley final drive belt and the automotive timing belts certainly add some evidence that belts in these types of applications can have SIGNIFICANTLY longer shelf lives (with regards to not degrading too rapidly just from ambient exposure over time).

Certainly I would think the Harley drive belts have much higher loads on them, even considering what I think is a larger size belt.

I don't know that I'd consider the rpm differences that much between an automotive drive belt and Ducati, not unless we're talking a race environment. But of course, the difference in replacement intervals are just staggering, off the chart different. Perhaps radius is a bit tighter, but is it enough to make THAT big a difference?

I guess part of my attitude stems from watching maintenance intervals across the entire industry both be extended as materials and designs have improved, and also be ignored by the average consumer with only the most extreme examples usually resulting in a catastrophic failure. I realize that is a HUGE generalization, but it certainly suggests that manufacturers are purposely conservative with their recommendations (perhaps as much to counteract the public's tendency to stretch it out anyway as it is to protect their reputation by preventing problems).

Again, I'm not telling anyone what to do here. But the overwhelming evidence that I've sourced from multiple owners of Ducatis is that given reasonable/gentle usage, the OEM replacement interval of time alone seems uber-conservative.

No, I'm not about to use it till it breaks for a data point.

I AM trying to make sure that we at least hit the 7500 mile mark by the close of year 4 and we'll just go ahead and do the whole she-bang (belts and valves).

But I'm certainly not going to stay up late at night worrying that 3 year old belts are gonna go on my bike with only 5k miles on em.

-Shelf life is not the same as service life. Shelf life is idea storage condition, with out any loads.
-Engineers don't use loads to design, its about stress (which takes into account cross sectional area(..or whatever type of load geometry that is important), so the larger belt with higher load is the same thing is a lower load on a less wide of a belt). i.e. there is no comparison of force that is valid.
-The pulley diameter has a SIGNIFICANT impact for two reasons. First is the moment arm, the bigger a pulley is, the less load it applies on the belt (consequently, you can increase the load by decreasing the pulley diameter , this is why it is easy to leverage a 1ton block with a 10ft pipe, and not so easy with a 1 foot pipe). the second reason is that the smaller diameter leads to increased velocity at the leading edge, faster moving belt = larger kinematic stresses, which if you are looking at it from an energy stand point, double the speed actually squares your energy input. So while the force between the two comparisons (harley final drive and the ducati pulley) isnt really a reliable stand point, the pulley diameter is.

Lastly, as materials improve and testing becomes more involved, we dont just say, well use the same conservative factor to reduce the service load. Instead we make the part smaller, and load it closer to failure, since we know when it will fail. So it should be even MORE important for us to follow the maintenance schedule.

That said, even if there are dozens of people here (myself included) who have safely gone past 2 years,12,000 miles. Just dont try to sell it to someone without telling them the ramifications.

That and more.  My dad never changed brake fluid or transmission fluid in his cars and never had a problem.  Guess I should do the same?  Or maybe that is why I couldn't stop his Lincoln from 100 MPH?

Funny because my dad never changes his oil. His 1988 toyota 4runner had the same oil (actually, thats a lie, the gasket blew at 150,000 miles and it required a top up every 5,000 miles so theres your oil change) for its whole 350,000 mile life. About the only thing that was changed was the spark plug (fouling from burning oil). It lost a cylinder in its last 5,000 miles of life before hitting the scrap yard. If you dont particularly care about your car, or its reliability (though it was deadly reliable) id say its cheaper to NOT change your oil and just buy another freaking car when it dies!

[Kev M]

Sorry for misusing terms, but in-service life, stress, or bend aside, my anecdotal points remain.

I'm not trying to sell it to anyone who doesn't understand the ramifications, or honestly to anyone who does other than to explain my conclusions after researching with many owners and techs.

I've spent my life around engineers, and was raised by one, so I understand their reluctance to abandon math for intuition and experience, but I also think even the best engineering calculations are proven or disproven in testing, and THAT'S where anecdotal evidence comes into play.

[Yogi]

Interesting.
Has anyone actually experienced first hand a broken belt or is it all what if?

My Dealer says it is OK to do 4 years on a belt. They have not had any snap. All they say is check the tension and see if they are showing signs of deterioration regularly.
I hear lots of horror stories about belts braking on many forums but there is not much evidence, most breaks seem to be due to neglect (Tension).
I just searched this forum and I could only find one snapped belt thread.
The comments about pulleys being small unlike cars which is a reason for more frequent changes is a bit lame. The crank pulley on my M1100 is more or less the same size as that on my Lancia (car) admittedly the cam pulleys are way bigger, but a lot of cars now run balancer shafts with tiny pulleys the same size as the cam pulleys on the Monster, these camblets last considerably longer.  And if you factor in heat how can an exposed air cooled engine run hotter belts than a transverse mounted encased belt turbo charged engine?

It is a shame no one has solid proof other than hear say. You pay your money you take the risk.

Edit
I found this if your interested some FACTS on belts from Gates http://www.gatesmectrol.com/mectrol/index.cfm?location_id=5319

[coduc]

From a design perspective, I would want to make sure that the valves open and close at the right time relative to the crank/pistons.  There will be minor changes to the valve timing when the belt stretches (and it does every second the engine is running), since we all know the load on the belts is not uniform.  What this basically means is that the cams are being tugged around by the belts and sometimes the cams might be "ahead" of the crank and sometimes "behind"  thus, the timings is very minorly "variable".  If you keep your belts replaced on a regular basis, the stretch and flex experienced over the service time will be more uniform, thus performance will be more consistent (all else being equal).

From a racer's perspective, trying to keep the engine running and bike performing as consistently as possible is the best way to achieve race wins.  The practical result from consistent bike performance on a road bike is reliability/consistency.

Ducati's main goal is to achieve customer satisfaction.  They gain nothing if a customer bombs an engine because the factory service schedule is set to aggressively. In fact, it is to their detriment because then they will likely have more warranty claims (which cost them money).  Also, Ducati has only a very small amount of experience with the bikes they sell when they initially put them up for sale.  But of course, at the time they put them up for sale, they have to make some kind of recommendation about when to change parts and they can only go on past experience and how good they feel about the new design.

In aircraft design, fatigue/maintenance limits are defined by calculations and mfr experience at the time of certification/approval.  As customer experience is reported back to the mfr, the mfr adjusts the service times/limits accordingly.  Ducati does the same thing, only they probably don't worry too much about revising old models since they are a lot more disposable than a 747 engine.

I've had my 750 for 5.5 yrs and changed the belts after about 4 years and 15000 miles and only adjusted them a few times in between.  I am just now adjusting the valves.  This is my own schedule based on how the bike feels to me regarding power delivery and also due to my laziness.

Most people buy Ducati's on emotion not on the maintenance cost, and Ducati knows this.  They also know that people buying Ducati's probably have the cash to change belts to make sure they can ride the bike down to the coffee shop and show off their coolness to all the other bikers.....   

[He Man]

Interesting.
Has anyone actually experienced first hand a broken belt or is it all what if?

My Dealer says it is OK to do 4 years on a belt. They have not had any snap. All they say is check the tension and see if they are showing signs of deterioration regularly.
I hear lots of horror stories about belts braking on many forums but there is not much evidence, most breaks seem to be due to neglect (Tension).
I just searched this forum and I could only find one snapped belt thread.
The comments about pulleys being small unlike cars which is a reason for more frequent changes is a bit lame. The crank pulley on my M1100 is more or less the same size as that on my Lancia (car) admittedly the cam pulleys are way bigger, but a lot of cars now run balancer shafts with tiny pulleys the same size as the cam pulleys on the Monster, these camblets last considerably longer.  And if you factor in heat how can an exposed air cooled engine run hotter belts than a transverse mounted encased belt turbo charged engine?

It is a shame no one has solid proof other than hear say. You pay your money you take the risk.

Edit
I found this if your interested some FACTS on belts from Gates http://www.gatesmectrol.com/mectrol/index.cfm?location_id=5319

Just a few comments: your thought on the pulley size being a lame excuses i the lamest thing ive ever heard. (see how that works?....hint: it doesnt matter if its lame or not, science isnt as cool as you think it is sometimes). BTW If you click on the link you provided the first thing they say is how the belt is affected by the timing gear. Im putting this in layman terms since its a pretty technical article.

Anyway, i should probably point out that belt failure isnt caued by the belt SNAPPING (though it can certainly fail that way). Ive never heard of a belt snap (on a ducati, and the only one that did was caused by CA cycleworks bouncing a shit ton of weight on one). Belt failure comes from the strands coming loose (its the glue that fails) and the strands get caught in the pulley.

[Howie]

I've seen two types of belt failures on Ducatis.  The rubber itself becoming hard and brittle or the cords failing.  Strength comes from the cords, power is transmitted through the rubber.  As I said before, I've been working on cars with timing belts since 1974, before many of you were born.  I also owned several of them, two which failed prematurely.  And, yep, one day when visiting a dealer I saw a rather hard ridden 748 (red belts) that came in for the 12k service with the belts held together by a few cords.  One more start up, kaboomy! I also saw belts last four and five times the interval.   

Since we don't get Lancias in the US I am not familiar with the layout of the timing belts so I can't comment, but balance shafts generally have little load and the belt might not wrap around them as much as a cam sprocket.  Also most cars do not have you release the tension on the belts to adjust valves, then retension, an added stress.  Again a maintenance interval on a part like that will be appropriately conservative, but to not follow the schedule is like not putting money in a parki8ng meter in NYC.  Save a quarter, possibly loose hundreds and a lot of inconvenience.  Belt breaks you will at least need some valves at about you are looking at over $100 per valve plus labor at a minimum, a trashed engine worst case scenerio, and if it happens far from home?

[He Man]

I dropped a valve at highway speeds and did a ton of damage. $1000 for both heads to get new valves, valve guide and gaskets. This doesn't even  include the labor to get the head off and back on. I ended up just getting a new motor entirely! Failure mode was different bit the damage was the same. Not worth it!

[Estoma]

Preventative Maintenance beats Corrective Maintenance on any day, even on a good one.  I am forever confronted (challenged) on the beat-to-death subjects of Safety Factors and of ‘Over Engineering’.  Truth be told; your life, limbs and wallet have probably been thankful many a time for those without you even knowing about it.  These factors empirically take care of the Conditions that cannot reliably be calculated or foreseen – or which might simply not even have been anticipated. Where they can be, they are incrementally considered – which is why Service Intervals are increasingly improving.  Everybody uses their Bikes in different ways; some nurse them, some race them, some abuse them, neglect them.  Some will start them cold, smoke the rear tire for half a minute at top revs to impress their swaggering mates and then shut it down again.  Sometimes you miss a gear, sometimes you lug it and stall it.

And there is NO WAY that you can compare the highly strung, erratically loaded life of a Timing Belt to an H-D Final Drive, or to tires.  Each individual component faces unique Engineering Prerequisites and bespoke Design Conditions.

Do yourself, your Bike, its next Owner and your Wallet a favor and follow the Manufacturers Recommendations.  Always.  It never seizes to amaze me how many Users of a Product will forever know better than its Originator.  There is no problem with fitting higher spec Consumables (e.g. best-in-class Timing Belt, Oil Filter Brands) or even servicing more frequently than mandated (e.g. Oil & Hydraulic Fluid Changes), but if you choose to undercut it might just be at your own peril.  The Brits quite rightly call it; being penny-wise and pound-foolish.