One of the things that surprises me when I write posts are the reactions I sometimes get, specifically the questions that often leave me wondering how people interpret or comprehend what I've written. It makes me realise how hard it can be to be clear and get what I'm trying to say across. Compounded by my tendency to ramble and digress and straight up forget what I was rabbiting on about in the first place. So I'll put in some more belt info, and try to respond to some of the comments and questions.
Another thing is that (especially with cam timing) people ask me for "the good numbers", as if there's some sort of secret squirrel component to what I write. There's not. What you see is what you get.
The old Gates belts were available for all the Ducati models pre 98 external to Ducati via Gates distributors. The three part numbers were "cancelled" in Australia last year, not sure about the rest of the world. They were all differing construction types, which I found a bit interesting.
T934: the 900 round tooth belt - 900SS, M900, 906, 907, ST2. 1st generation construction, NEO - Neoprene rubber fibreglass tensile cords and nylon tooth facing. Interesting that the belt introduced last was the most basic construction. Never gave any issues.
T819: the Pantah square tooth belt - all small blocks (non 900) up to 1997. 2nd generation construction, HTN - High temperature neoprene rubber, fibreglass cords and nylon tooth facing. Never gave any issues. When the Pantah was first released, they had Pirelli belts which were rubbish I'm told by people who worked on them. And gone before my time. I have also seen Continental belts fitted to these motors.
T917: the 4V belt, also fitted to Renault R19, which ran from 89 - 96 according to the Gates book. 3rd generation construction, HSN - Highly saturated nitrile rubber with aramid fibre loading, aramid or high tenacity fibreglass cords and nylon tooth facing. The problem belt (from 98 onwards at least). The interesting thing is the aramid part. Aramid is a generic name for what is better known by name brands such as Nomex and Kevlar (both owned by DuPont). So these belts it appears had a Kevlar component, which was allegedly the big point of the red letter belts.
So to clarify, the only Ducati belt made by Gates that gave any issue was the T917 - available via Ducati or Gates. And the issues only appeared as a consistant problem in 1998, by which time Ducati seemed to have realised there was an issue as the "2 year replacement" directive was communicated to the importer (ours at least) before we had experienced it.
Why there was an issue I don't know. Lots of theories were expounded, but I like facts backed up with evidence and there didn't seem to be enough of that to generate any conclusions. Lots expired down the front straight at Philip Island, but lots didn't. They just broke on bikes that were more than 2 years old, but had done less than 20,000km. We also saw belts break that had been fitted at 20,000km services, but not replaced again within the 2 year window. Yes, the pullies are quite small compared to most automotive applications. And, on the 4V, there are quite extreme changes in direction compared to what you see in most automotive design. But, anecdotal evidence of belt life before and after, especially with the later belts, would indicate that the actual engine design is not "the" issue.
The Red Letter Belts, or whatever you wish to call them, were introduced in 1999 or so - I don't actually recall now. The main claim to them was that they contained Kevlar. All still made by Gates and marked as made in the UK, but not available outside of Ducati. Some were a bit more expensive, the Testastretta belts a lot so.
Whether or not all the red letter belts actually contain Kevlar, I have no idea. If you can find someone at Gates who does know, pass it on.
As to the two year replacement interval thing: Firstly, I have no interest in arguing this in the slightest. Absolutely none. Believe it. Don't believe it. I don't give a rat's arse. But every official Ducati workshop manual from 2000 until the MTS1200 has had the two year replacement regardless of km specified. At the bottom of the scheduled maintenance chart or on the next page, it will have the note corresponding to the (*) or (1) after the Timing belt line saying "Replace every two years, in any case." With the MTS1200 and Diavel it became 5 years. As I'm not part of the dealer network, I didn't get the official explanation as to why.
As to how often I change my belts: I have only had one belt drive bike in use long enough to require belt changes, but then again it's also on its third engine in its time with me and there's been a bit of idle time. I think only the 750 engine has had belts in it long enough to need them to be replaced, and I only did that when I realised (after noticing the dates on dyno runs) they were over 5 years old. I'd guess the belts in the 851 are getting on for 15 years old now, but it hasn't run in 12 years so that's no big deal. Everything else has been moved on before time. But I'm a tight arse too, so any belts in my bikes will be in there for as long as I can withstand the niggling paranoia of impending doom.
I've not used any of the Dayco belts. As the Australian distributor for California Cycleworks products, I use the Exactfit belts as the aftermarket option.