Hi , I recently bought an ST4S from build year 2004. It has got about 28000km or 17500 miles and I don't suspect any fraud with these numbers at this point. I have done about 300 miles on it and I started to notice a vibration in the engine. It runs very smooth up to 5500 rpm but a vibration starts to build up from 6000 rpm until it reaches the redline. The intensity of the vibration just increases with the revs. It's not that the whole bike is shaking but it's already unpleasant at 6000rpm and I don't see myself doing alot of miles on it in this condition. Another problem I have is throttle body related I think. When cold the engine just backfires into the airbox alot. Once the engine is hot this still happens but only very occasionally. Could this vibration be linked to the backfiring problem or I'm I looking at 2 different things and should I start to look at the main bearings or the flywheel. When I bought the bike it had brand new oil on it. I will replace the old one with new one just to see how it looks. Any ideas or tips will be greatly appreciated. DeScheep
Cause of the backfire is lean running. Ideally you need your throttle bodies balancing and the fuel trim adjusting.
I would suggest that the two problems are linked and it sounds like the fuelling issue is causing unburnt fuel to ignite as a backfire. This could be down to one or more factors such as the Throttle Position Sensor (TPS) needing to be adjusted, throttle bodies balanced, ignition timing or component issues. All of the above would cause uneven fuelling or ignition which would in turn make the engine vibrate. There are obviously other things like the fly wheel coming loose that might do the same thing and I'd probably start by ruling that out first, for no other reason than failure could be catastrophic. However, my money is on the fuelling or ignition being the route cause. Good luck with the bike and keep asking questions as you try and solve the issue. They're a really helpful bunch on here
Thx for the replies I had some time today and pulled of the alternator cover and drained the oil. I found no surprises so that's a good thing. The oil and drain plug were clean. I did not have the right tool to remove the oil screen so I will do that tomorrow. I have my doubts about the small alternator bearing so I will replace that before assembling everything tomorrow. One thing that bothers me is the fact that everything came appart so easy. The hoses from the cooling system required no effort at all to remove and the coolant was clearly brand new so some work has been done on the engine but what????? Since the weather is bad for the next week I will do the belts and valves as well before taking it to the dealer to sort out the fueling. All maintenance history I have is on a word basis so I won't take any risks. I have never done any valve adjustment on a Ducati before so all tips, articles or videos on the subject are welcome. DeScheep
Hi, It's been a while since my last update. I gave the bike a full maintenance and decided to repaint the alternator cover since the paint was badly damaged near the sprocket. This took me a while and by the time my bike was back together the dealer his holiday started followed by mine. I got the bike back early this week and the tune up on the test bench transformed the bike. It is clearly running much richer at idle now. No more back fires in the airbox and the vibrations higher in the revrange have disapeared. At this point I still have some clutch issues wich I have to investigate, but nothing that can't be ressolved. DeScheep
Glad to hear you are sorting things out, but my 2002 ST4s had main bearing failure due to oil starvation at around 30k miles. It started with a vibration just the way you describe. The oil screen and filter were fine for me too, but the Ducati tech who diagnosed it for used a long pipette type device to extract oil from deep in the sump and it had white-ish particles in it that he concluded could only have come from the main bearings. He was right and showed me the offending items. Fortunately, I had no damage on the crank but the rebuild was bloody expensive. Worth a shot if the vibration persists.
Main bearings went on my ST4 at 12k. Started making a hard to trace 'whiring' noise, that sounded like worn bearings, but seemed to occur all of a sudden. Long story short, Rich at Luigi Moto diagnosed the bearings and correctly predicted that the crank had been shimmed too tight at the factory. He was able to tell from the distinctive sealant that the engine had never been apart from new. One of the bearings just fell apart when he tried to remove it, so I guess I was lucky to have caught it in time! New bearings and a propper rebuild sorted the problem. Top bloke is Rich
