Ducati Monster Forum

Why is it that Ducati recommends changing the timing belts at 12k miles, but most car manufacturers recommend changing them at 60k-100k?

the belts are turned over a much smaller wheel, resulting in higher heat and higher stresses on the belt. also, i think most car engines are non-interference, and thus if you break a belt you're just stranded, and not blowing up the top end of the engine.

or that's the tale i've heard passed down.

Chris,

   In my opinion, mostly it's a "penalty for failure" issue. In your average auto, if a timing belt breaks, all that happens is the motor won't run, the pistons spin around a few times, and the valves stay where they were, no big deal. You'll have to put the new one on making sure you line up the timing marks. In a worst case scenario you could have bits of belt or chain flying around, but that's why they've all got scatter shields over them.

   Ducatis, and other high performance autos, like Ferraris, have "interference" valve design. This means that if the valve is open, and the piston comes up, it's going to smash your valve. Standard motors have clearence so that at TDC the valve can still fully open without obstruction. So, just like Ducati, Ferrari and other such manufacturers will recommend short timing belt change intervals.

  The idea isn't that the belts will break more often, but, since the penalty for failure is so high, change them with an extremely safe margain.

That's my .02 at least.

Justin

Hmm OK, I see the reason there. But we are talking about 5+ times the change interval.

I'm pretty sure my Nissan 240sx is an interference engine. But, it has a timing chain, not a belt...

A friend of my dad's had a Fiat X1/9.
It had a cambelt.
The change intervals were very explicit.
He went past it, and it shucked the belt.
Got the head rebuilt, as it was an interference motor.
Reassembled.
Went past the interval again, and shucked the belt.
Got the head rebuilt, again.
Reassembled, again.
Installed the race-spec belt, and was diligent in replacing the belt on time.
No more problems.

Ducati's interval may be conservative, but beyond that YMMV.

Most automobile ARE interference engines. Very very few are not. The only reasonably modern one I can think of right now is the older Ford 2.3 engines used in the early 90's Mustangs and Rangers.

I can attest to that with FHE, my Merkur with the 2.3 Turbo motor shucked a belt with no harm done (other than to my schedule, and my wallet for the towing).

If it wasn't for costs...and the fact dry chains were noisy...

we'd still have them and be happy.

+2 - my 86 ranger 4cyl broke a belt middle of no-where nebraska, and no damage done.

mitt

I'm pretty sure they aren't, though many of the newer high performance motors may be, I've seen a lot of timing belts break on cars and it's never been a problem other than a delay.

I'll venture to guess...

Do you think that RPMs have anything to do with belt life?  Guessing that over the life of a Ducati belt it is being subjected to much higher revolutions than most auto's.  Of course I have absolutely zero factual evidence to back that thought up... just a guess.

Back in the '70s when compression was lower interference engines were the exception.  Now it is the opposite.

Here is a good resource for finding out if your car has an interference engine:
http://www.gates.com/part_locator/index.cfm?location_id=3598&go=Interference

Back to our bikes; small sprockets, heat and quick RPM change shorten belt life.

Another characteristic of our engines is the uneven firing order, the crank doesn't spin as consistently as you might think.
The variations in crank speed do spike the loading on the belt.

Nearly all automotive engines are more than 4 cylinders, and generally heavy flywheels compared to our bikes, so the cranks turn pretty consistently.
The cams generally serve all cylinders, and all those lobes tend to smooth out the loading.

oooh, good info, didn't know that  [thumbsup]

As a tech for 20 years, I gotta state you are wrong. There are MORE non-interference engines than there are interference ones. Primarily Honda, Nissan and high perf engines from other mfg's were and are interference. That's why I buy Toyota's non-interference. Plus they are back to using chains!  [thumbsup]  And if ya wanna get totally non-interefence, there is my RX7, no valves, period!!  8)

What I find wierd is that on the newer engines that are at the new 7500mi service interval, Ducati has not aligned the T-belt interval to match. I should be changing them at 15K not 12k. No matter really, I'll be inspecting them at 12k and most likely run them til 15k anyway.

I recently saw a nissan diesel that had broke a belt and trashed the engine big time.

Hmm... I guess VW, Audi, older BMW six cylinders, Subaru, Suzuki, Mitsubishi, Hundai and I'm sure some who i left out don't count ;)

Most of those fall into that "performance" engine category but some of the others are a surprise. Guess things have changed a bunch since I bailed out of the automotive trade.

Hypurone,

I'm not wrong at all.

Go on the Gates website listed, it shows which engines are Interference or not. I'm having a tough time finding ANY 2000+ model vehicle that is a NON interference engine. I'd venture to say that many are not what you would consider "performance"

I don't remember the orignal post stating 2000+ as a qualifier. Most every Toyota except their limited diesel designs are non-interference. As well as most domestics w/o perf driven layouts. Since the inception of timing belts I still think if someone went thru every car made and all their engine revisions, there would be more non-interference engines. But I think we digress...

I've been told my Honda Civic is an interference motor and if the belt goes I'll mash some valves.

There are several reasons to change the belts on a Ducati more often than on a car:
1) Many bikes sit still for several months in the off season.  The belts can take a set during this time and become more brittle and more likely to break.
2) The belts go over some very small pulleys and flex more than on a car making them more prone to failure.  Double that on 4v bikes where the belts are tighter, make more bends, and flex significantly in both directions.
3) The 2v bikes are air cooled and so run very hot compared to water cooled engines.  The belts sit right next to those hot cylinders and take all that heat.

While the belts need to be maintained it's not terribly expensive and only takes about 30 minutes every 2 years/12,000 miles.  Not a bad price to pay for owning an exotic Italian moto.

I like the belts.  My last bike was a modern air cooled inline four with a cam chain and the engine was noisy as hell and spit a lot of high frequency vibes out to the handlebars and foot pegs.  The Ducati is much smoother by comparison.  One other thing, if you take the covers off they look wicked cool when the bike is running.

Scott

Covers are off on mine, but I think a timing chain would look cool in that situation too. Just two more chains to lube...