Just to add a discussion point.
Like most Ducati owners I try and replace my belts at the recommended intervals , or close but I have afriend who ahs the dame belts on his ST3 after 25,000Mls and says there is not problem with them and is happy to continue with them.
He says that should the belt(s) break there will be no damage caused as the valves will not damage the heads or be damaged themselves , the bike will just stop running.
I know the difference between the ST4s engine and the ST3 is quite large but was surprised by this statement (he is an engineer so didnt want to get into an argument with him as I dont know the motor)
What do others know , are the ST3 motors that bullket-proof or is he wrong ?
I'm an engineer also and that is just whacky. When the belt lets go, it is going to thread through the system in some manner, similar to a chain snapping. Think about how well seated our belts are when replacing them. Those different running speed are going to ensure a valve meets a piston.
Even if it were to totally dissappear, the cams have a certain inertia, spinning at half engine speed, 2k or more. The closer springs will not come to rest in one revolution, or less. Not good.
Worse than that, the ST3 has a SOHC. Therefore, all three valves are on one cam. Unlike the ST4, were all valves seat without a belt, there will be some portion of the cam rotation where the valves will be held on lobe.
Not good. I'm just sayin'.
Have a good one.