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ST4S: New owner with various frustrations

6K views 35 replies 14 participants last post by  tonered 
#1 ·
Hello all,

I'm back in the Ducati fold again after writing off my 888 last year. Based in Nottingham UK and joined this forum as there seems to be a lot of excellent ST knowledge here! A few months back I bought a recently neglected (and so cheap) 2002 BBG. So far its been pretty much an exercise in frustration getting it running right! Jobs done so far;

Broken mirror spring mount. Several fairing tabs repaired. Leaking fuel tank traced to a failed seam which is now fixed with tank sealant. Oil, belts, fuel and oil filters changed as bike not serviced properly for 5 years (though only 3000 miles previously). New rear pads (one had no material left). Intermittent weird dash coupled with starting failure traced to failing ignition relay. Wobbly dash traced to failed anti-vibration mount. Rear suspension ride height adjuster was in its original position so was taken off, loosened off and rear raised so the tyre is just off the ground on centre stands. I am aiming to strip and rebuild the suspension over the winter at the same time as I do a valve etc service.

I love the riding position and seems just on the right side of sporty to me. Even better is a steering lock that actually allows you to turn sharp corners. Handling wise it feels great though the front feels a little light after the 888. The extra power of the 996 engine does not seem too obvious after the 888 though picks the front end up easily pulling away in first. It generally feels a little bit too civilised to me after the 888 (which is maybe why it doesn’t feel much faster) so I think I need to liberate some intake and exhaust noise :D I am still left with 3 concerns that are proving harder to sort;

1. Brakes. I have the pulsing brake lever at low speed and brake shudder at medium and faster speeds. I checked the nearly new Brembo discs for run-out on my lathe and they both seem OK though obviously difficult to check accurately with semi-floating carriers. Disc thickness checked with micrometer at 3.90-3.95mm for both discs over the whole surface. Freeing the bobbins didn't help. Cleaning discs with angle grinder (wire attachment) didn't help. Converting discs to fully floating (by cutting out the star washers) didn't help either. Brake pistons all free and cleaned. Head bearings, wheel bearings etc all OK. I've seen all the threads on this but don't understand how I can have a pulsing front lever if the thickness is constant and the discs are floating. I’m tempted to try a pair of the cheap Chinese discs just to see but am open to suggestions of what else to try.

2. Tachometer. Initially OK but went loopy after the last run (probably not helped by the failed dash mount). Currently reading 4000 rpm at tickover and barely moves when revved. Tightening the 3 brass screws at the back made no difference so I cut it open. There were no obvious problems with the circuit board so I remade all the solder connections in case of a dry joint and put it back together to find no difference. I have checked the voltage feed and earth as OK. Before I try and track down another tachometer can someone confirm what voltage I should get at the feed from the ECU just in case I have an ECU problem? Currently 11.5V DC with ignition on (ie about 1 V less that the 12V feed) and drops to ~2.5V (both AC and DC) when running. The voltage doesn’t appear to change when the engine is revved. I don’t have an oscilloscope to check the wave form but may be able to borrow one.

3. Vibration. The engine feels slightly smoother pottering around town below 4k rpm than the 888 which is nice. However, at higher rpm it shakes/vibrates when the throttle is opened wide which the 888 didn't do to (except at really high rpm). Cruising on a low to moderate throttle is fine but giving it a handfull eg at ~6k range brings on the vibes. Mirrors, dash and rev counter all vibrate and the last ride was causing me really bad white finger (I do suffer some times). Thus, I am wondering if the 996 engine is just generally more viby or if something is loose/not right somewhere (I've already checked pretty much all bolts including the main engine mounts). The engine sounds super smooth with no abnormal noises and the oil and screen were clear of anything nasty.

Any suggestions much appreciated!! Thanks, Keith
 
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Discussion starter · #8 ·
From my recollection the discs should be 5mm with a min of 4.5 mm so they probably need replacing anyway , pulsing , or not.

Does the engine run rough when revved high in a low gear ?
It could be wheel imbalance occuring at higher speeds.
Otherwise it probably just needs a good service TPS/Throttle balance to sort , it should be smooth...
The discs are pretty new but are 4.0 mm discs rather than the correct 5.0 mm items. I'm assuming this is not ideal but I guess OK as that is what the earlier bikes ran.

Its not wheel balance as its smooth on part throttle but gets rough as I wind the throttle on. Thanks for confirming that it should run smooth. Hopefully a throttle balance etc will sort it. The plan is to strip out the suspension etc over the winter so I'll do the valves etc then.

Keith
 
Discussion starter · #9 ·
Hi Keith and welcome to the forum.

It's very sad to hear of a very lovely and very rare 888 being written off. That would be my ultimate Ducati.Forgive my ignorance, but what's a BBG ?
The 888 is still alive as it wasn't too bad. I bought it back from the insurance company and sold it to a mate. Its now back to being immaculate again. The 888s are lovely at 70 mph plus and for trackdays but I am just getting too old for the riding position. My right leg used to cramp something chronic......

Keith
 
Discussion starter · #10 ·
Sounds like the previous owner didn't keep it up all that well. My tach started getting weird so I disconnected all the terminals, clean everything up well and reconnected it with dielectric grease. It's good to do that on all of your connections really.

I never rode a 888 but maybe the gearing accounts for the difference. And/or the rough engine means that a tune up is in order. A smoother engine around town than the open road is the opposite of my experience.
The previous owner shouldn't be allowed to own a Ducati. It was immaculate when he got it and had just had a full service at a specilaist. When I got it 3000 miles and 5 years later it was a much different story.....

I am hoping a tune up may help. Throttle balance seems possible from what you are all saying so I'll see if I can dig out the vacuum gauges. The ST4S is smooth around town only in comparison to my 888 which was a bit of an animal. Any more than a sniff of thottle below 4K will certainly bring on the shakes but thats standard fare for a Ducati as I understand it :D

Keith
 
Discussion starter · #13 ·
Yeah, I meant earlier Ducatis in general. My 888 had 4.0 mm discs as well on what seems to be the same calipers and that braked pretty good.

Keith
 
Discussion starter · #17 ·
Well, I seem to be making some progress! Rev counter fixed and working 100% again (see separate thread). The dash is also now bouncing around less now I fixed the one rubber mount that had fractured. Due to encouragement from you, I checked my TPS and it was high at 220 mv. Reset that and then found that the TB balance was a bit out as well. Got that spot on at 4000 rpm on the fast idle and then balanced it at tickover with air bleeds. The TPS was reading zero on DucatiDiag at tickover so I reset that that with the software and it now reads 2.5 degrees which sounds about right. The end result is a more robust tickover and a much smoother engine. I no longer have the shakes at full throttle. All I have now is a steadily increasing relatively slight vibration above about 8,000 rpm which is what my 888 used to do. Much happier!

I also stripped the discs off again. I sanded them lightly to an even buff colour and cleaned off the paint on the wheel flange in case that was throwing them out. Still no better :( I can clearly feel the lever pulsing at relatively low rpm so I dont think it can be anything else now! Thus, looks like I am going to bite the bullet on discs. So, do I go with the Chinese discs or try and track down a good second hand pair? I dont see why I should pay a vast premium for Brembo discs when they seem to warp so readily on this bike!

Thanks, Keith
 
Discussion starter · #19 ·
Yep, that makes sense. My 888 had the early style TB without air bleeds so there was less to play with. I still need to do valves/rocker check over the winter so balance will get done again after that! Certainly good enough for now though :)

There are a couple of sets of discs on auction on ebay in the UK so I'll keep a careful eye on those. I need to do something as braking is not nice. Light and heavy braking is not too bad but 'normal' braking is pretty unpleasant :eek:

Keith
 
Discussion starter · #24 ·
Oh, I'm pretty certain its the discs. As said above, I have 'spun' the bobbins to free them off which made no difference. I then cut out the star washers to convert the discs to full floating which made no difference. I then sanded the discs and removed all paint off the hub flanges which made no difference. Well, actually thats not true, the 'pulsing' through the lever at low speeds is now much more obvious. Pistons all clean and free and wheel bearings and headstock bearings are fine. If there is anything else to check then please let me know as I've reached the end of my list :)

Keith
 
Discussion starter · #31 ·
Thats certainly an interesting tip for checking head races. I've still not made further progress mainly due to a 3 day working week and job uncertainty which is curtailing spending. If I was absolutely certain it was the discs I would spend the money but there is still that nagging doubt. Its no big deal if I dont get it sorted this year but I want to do at least one track day next year but not with those brakes :)

Keith
 
Discussion starter · #32 ·
I took a risk on some second hand discs. It was a bargain price as the listing was mis-spelt and when I got them I was delighted to see they were nearly mint. I slapped them straight on using the old pads and without bothering to free off the bobbins and straight away its clear that it brakes beautifully now :D Thus, confirming that my discs were the problem. I'm sure they were not warped and the micrometer suggests that slight variation in thickness was most likely the problem. I am assuming that they must have worn that way as there were certainly no deposits on the metal.

Unfortunately, the bad news is that near the end of a fun blast it started surging and firing back though the air box. It then completely dropped one cylinder :mad: I'm hoping its just a bad plug or loose connection but this bike is really making it hard for me to like it.....

Keith
 
Discussion starter · #34 ·
The disc surfaces on the 'old' dics look fine and are clearly nearly new. I could see no warping when spinning them on the lathe and the full floater conversion should have coped with a certain amount of movement any way. I could measure a small thickness discrepancy around the disc with a micrometer(cannot remember how much) so that must have been the culprit and would certainly cause the pulsing through the lever. I have to assume they were fine from new so all I can think of is that the hardening process was not uniform around the discs and they have worn this way.

I agree I should fit new pads as best practice. However, its obviously also not best practice to fit second hand discs :) The pads are nearly new and the brakes are so much better so I'm going to stick with what I have.

Keith
 
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