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Thread: Summer running - 2000 Ducati ST2

  1. #181
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    28th January 2015 - 16:17
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    2000 Ducati ST2
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    Well, it looks like I wasn't correct about the inlet manifold flanges. The bike's test ride showed improvement but not a fix. I took the bike home and got the throttle bodies out and onto the bench, to go looking for vacuum leaks.

    While doing this I noticed that I'd managed to fold and nearly guillotine one of the injector O-rings. These really want grease or similar on reassembly, they roll very easily if they grip on the outside while being installed. However I don't think that this was the problem.

    I got diverted briefly by filing off the last remainder of the mould flash lines on the throttle bodies where they connect to the manifolds. Rubber doesn't fold perfectly into the 90 degree valleys either side of a raised ridge like this, even if it's a small feature - a smooth surface is better, even filing by hand. There was dirt at the root of the mould flash line, indicating air movement. These would be pinhole air leaks though.

    The greasy dirt around both throttle body return springs finally convinced me to have a look at the shaft seals, as the last remaining place for a significant vacuum leak. The first step was to remove the TPS and get the 8mm push nut off the throttle shaft. There's basically no way to do this without destroying it - I cut both sides of the diameter with a Dremel and broke it away, after failing to lift it by prying with a screwdriver.
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  2. #182
    Join Date
    28th January 2015 - 16:17
    Bike
    2000 Ducati ST2
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    Lower Hutt
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    The next step was to remove the throttle butterflies. I had to be careful about cleaning filings up before allowing the throttles to close again - rags, cotton buds, compressed air, and a magnetic pick up tool were used. The photos do most of the talking but something needs to be said about the photo of the throttle butterfly: it was installed on an angle. It'd be quite difficult to keep it straight, the way it's designed.
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  3. #183
    Join Date
    28th January 2015 - 16:17
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    2000 Ducati ST2
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    Lower Hutt
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    The throttle shaft seals look like they are the issue after all. There's a lot of dirt underneath them and in the shaft's plain bearing - cotton buds used for swabbing came out filthy - and the seals themselves are borderline loose. They're barely holding themselves in place. The outer diameter of these seals is also a cup design, similar to the inner lip, and is tapered. The seal to housing interface is really only on the outer edge.

    One of the four seals appears to have been cut by the throttle shaft. I can't be sure if this was during work today or during installation. A close look at the throttle shafts showed that they're covered in sharp 90 degree edges which will pass over the seal during installation, and the cut made for installing the throttle butterfly has left positively raked knife-edges on one side of the slot.

    Replacing the seals may be a problem. Apparently they're an unusual mix of sizes - 8mm inner diameter, 0.150" high, 0.450" OD (or thereabouts). Note that 5/16" is very close to 8mm, though, clocking in at roughly 7.93mm. Spare seals aren't available from Ducati. Total replacement of the entire throttle body is called for instead, which at Euro 740 isn't exactly free... CA Cycleworks made up some aftermarket replacements, see:

    http://ca-cycleworks.com/t-seal.html

    They look good but they're ex USA and they're also not reinforced. I think it may be possible to fit SKF 3044 grease seals as replacements, if the throttle bodies are modified slightly via a piloted 12mm counterbore and a drill press. The 3044s have the advantage of a metal ring holding the outer diameter. They'll press into place and then stay there. I'll have to check compatibility with petrol though.
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  4. #184
    Join Date
    28th January 2015 - 16:17
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    2000 Ducati ST2
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    Lower Hutt
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    Further work... I tested the free play in the throttle shafts via dial gauge and stand, with the throttle body clamped in the bench vise. All four bushings came in at between 0.90 and 0.80 mm. I've spent a bit of time looking at options.

    The bushings themselves are split, steel-based cylinders with bronze plating topped with a layer of sintered lead and PTFE. These have some commonly accepted brand names, like Ezi-Glide, Glacier, etc, but they're manufactured by a lot of companies these days. They're intended for low / no lubrication operation, which in a petrol soaked environment, makes a lot of sense. From what I've read, petrol does have some lubricating ability, but it's thin stuff, very low viscosity, and needs close running tolerances to carry any real loading.

    A comment on a forum concerning throttle shafts has stayed with me: if it feels loose, it is loose. These throttle shafts feel loose. Unfortunately I think I'm stuck with it. The shafts came in on the micrometer at 7.95 mm - so that's 0.05 right there - and the bushings are designed with a positive clearance of 0.30 mm as a brand new item. That's from checking the bushing's stated tolerance class and then looking up the ISO tables. Even if I can find the exact size (10 OD, 8 ID, 8 long), using a tap or an Ezi-Out to pull the old bushes and some sort of push tool to install new bushings won't really sort out the throttle shaft play. All that will happen is that I'll lose another week or two of riding time.

    The real way to do it is to install double-sealed ball bearings. This would reduce free play to almost zero, which adding another layer or two of seals. There isn't enough wall thickness on the housings though. The absolute smallest bearings I could find were 8 ID, 12 OD, 3 thick, unsealed, which would have to be installed in a throttle housing which has a 15mm diameter post for mounting the throttle shaft. That'd leave 1.5mm wall thickness of zinc-aluminium alloy. Also, the bearings were intended for ultra light duty - benchtop chart recorders and similar - and I had doubts about their ability in a rough environment.

    The last point is that this throttle assembly uses a spring return. There's no positive close cable. Maybe throttle shafts that are slightly loose is actually a safe choice here. So in the end I've left the stock bushings in place and simply changed the seals.

    The seals: I'd found an option online which featured a steel cup body and a spring on the inner lip, unlike the original all-rubber seals. Proper construction. Good... they were 12mm OD, slightly larger than the original 11.5-ish imperial size. I would have to bore out the seal housing, on center and reasonably in-line, to fit these.

    After some attempts with a drill press and then a lathe, both foiled by lack of tooling and difficulty holding the throttle body securely, I settled on making a one-off cutting tool and using a valve seat cutter guide to mount it on. The original throttle shaft bushings provided the guides. Proper tools are available but expensive since it's not quite a standard metric cap screw size. What's needed is a 12mm counterbore, an 8mm guide pin, and the relevant shank, all within the same system. Trade Tools offer the Ifanger system. I've worked with these before and the quality is outstanding but that's reflected in the price... at least $220 for one 3-part tool to cut four holes. Not really worth it for a one-off job. I lathed a bit of mild steel down to OD size, drilled and then reamed the interior, and cut holesaw-style teeth with a hand file. This worked, slowly, with a few re-sharpens needed along the way. I started cutting by hand but quickly found that fixing the cutter in the vise and turning the throttle body on top worked better.
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  5. #185
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    28th January 2015 - 16:17
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    The seals pushed into place by hand, basically a very light push fit, but I could feel the rubber engage properly. They're a lot more secure than the old seals were.

    The butterfly screws are worth mentioning as well. They're not standard fasteners... for this duty a very soft steel fastener, cad-plated, low profile high-torque head (ie Torx), is best. They're not easy to source, does anyone know a place?

    I tried using some standard M4 BZP cap screws. Didn't work. Either they were grade 8.8 or 12.9 but they were too hard to mushroom the tail ends of the threads after installation. That's got to be done. If these come off, they get sucked into the engine. Less obviously, if they come loose, the butterfly plates can shift. The butterfly can then jam at some partial throttle position.

    In the end I re-used the original screws. Setting into place was done by doing them up tight (by feel) and then centerpunching the rear of the screw, with the screw head directly supported on a suitable mechanic's socket. No loading was put through the throttle shaft or throttle body. The centerpunching was done in twos,one top, one bottom. This was intended to out-of-round the very end of the screw thread, from a circle into a figure 8, so that it locks into place on the throttle shaft's curved rear face. It's maybe a bit dicey - I've got just one thread clear of the shaft - but since I'm trying to lock within a fraction of a turn then perhaps this is enough.

    There were some fun and games getting springs, limit plates etc all back together but the throttle bodies are reassembled now.
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  6. #186
    Join Date
    28th January 2015 - 16:17
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    2000 Ducati ST2
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    Well... nope. The throttle body seals did make a slight difference but wasn't the main problem, my best theory is that the rough running is still a vacuum leak from the rubber boots moulded onto the inlet manifolds.

    As to why they passed the pressure test but have failed (as far as I can tell) by real world riding... I think it's thermal expansion between cylinders. The engine is actually alright when starting at cold. Two L-twin cylinders are connected to a banked pair of throttle bodies. As the engine warms up, the cylinders expand and lengthen, the distance between the two inlet manifolds increases, putting a very slight linear strain plus even slighter twist onto the throttle pair. The movement isn't much. Aluminium has a thermal coefficient of linear expansion of 17 parts per million per degree Celsius. The difference between cold and normal running is just 70 C minus 20 C, ie 50 C. The path length between the two manifold throats, center to center, at the cylinder head flange, is approximately 200 mm.

    This means a movement of just 0.25mm, roughly, but the rubber part of the manifold is very short. The rubber is definitely not 100% minty fresh and super flexy any more. Plus it may have been messed with by someone trying to do some porting. The pressure test was carried out with the manifolds separate from each other and the engine, so they weren't under this sideways strain, and so the test would not have shown this failure mode. So at this stage, I'll get the replacements in and simply try changing the manifolds.

    And why this hasn't already happened... maybe this is worth going through for anyone else regularly ordering parts through Stein Dinse. They're great guys but there's a gotcha to watch out for: everything I've ordered over the last couple of months isn't in three separate orders, as I've placed orders, and supplied in three boxes like we'd do here. As far as the guys at SD are concerned it's all my current order, ie ONE ORDER. So if there's one part waiting to be supplied, and I've ticked the box marked Send Only When Complete, well, everything from this week's order gets forcibly linked back to an order from five weeks ago. If I then place another recent order which has another time wait on a part, that restarts the clock and now everything waits on this new part, even if all the bits from the first time around have finally turned up. In short the delays could go on for quite some time. To be fair they are very clear about warning that delays can happen if you click that Only Send Complete button.

    This may be cultural, maybe this is a Germanic thing, maybe this is something that's just a normal part of the motor parts trade globally and I just haven't seen someone else do this yet... anyway after a phone call tonight and a chat, they'll send through a message with confirmation and revised payment and I can get the bits I need on their way. Ah well. One to remember for next time.

  7. #187
    Join Date
    3rd February 2004 - 08:11
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    1982 Suzuki GS1100GK, 2008 KLR650
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    Wallaceville, Upper hutt
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    Oil of wintergreen can soften age-hardened rubber. I tried it with the airbox-to-carb rubbers of the gs1100. Worked pretty ok
    it's not a bad thing till you throw a KLR into the mix.
    those cheap ass bitches can do anything with ductape.
    (PostalDave on ADVrider)

  8. #188
    Join Date
    24th September 2004 - 06:46
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    '76 CB550 Super Sport
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    On the road to nowhere...
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    6,679
    Quote Originally Posted by pete376403 View Post
    Oil of wintergreen can soften age-hardened rubber. I tried it with the airbox-to-carb rubbers of the gs1100. Worked pretty ok
    So does crc 5.56.
    "Every time you set your ass on a bike, you're playing a game of Russian Roulette between yourself and your own stupidity."

  9. #189
    Join Date
    28th January 2015 - 16:17
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    2000 Ducati ST2
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    Lower Hutt
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    Old Intake Manifold Autopsy

    So, the new parts arrived from Stein Dinse earlier in the week. I took a couple of evenings and changed out in the inlet manifolds.

    The first two photos show one of the old manifolds next to one of the new. The major difference between them is the rubber: the new one features rubber coating the entire inner surface. The seal between manifold and cylinder head is also now integral, instead of a separate O-ring.

    Test riding has shown a marked improvement (in both rough running and overheating) but not a complete fix. Some reading has told me that poor valve clearances can give a vacuum leak; testing at the last service showed that the clearances are right on the edge for opening shims and slightly over for closing. I've already seen that the bike has the OEM half-circle wire retainers, and I'd be amazed if they've been replaced since new. They're notorious for getting hammered flat over time and having clearances open up. I've placed an order for the MBP retainers, so once they're here it'll be worth checking and then setting valve clearances finely and also re-balancing the throttles.

    I've taken a hacksaw to the old manifolds and gone looking for the reason that they failed. There really isn't anything obvious. The rubber is still mostly bonded (it isn't on the inner or outer circular flat surfaces), and although it seems to have been disintegrating a bit on the inside, doesn't have clear pinholes or cracks. There's nothing wrong with the aluminium. What I'd taken for possible cracks looks instead like fold lines in the original casting. There is a patch where the casting was porous, but the gaps have been filled with rubber under pressure and sealed as well as any other part of the manifold. If a roughing tool has been used, it hasn't thinned the aluminium walls to the point of failure.

    I think the reason for failure is probably thermal expansion differential between rubber boot and aluminium body. Hard rubber has an expansion of around 80 parts per million per degree C, while aluminium will expand by 21 to 24. Since the rubber is bonded to the aluminium instead of clamped, sooner or later some part of the circumference will open up enough to let air in. For twenty years old they're not bad, but this design is guaranteed to fail by this mechanism sooner or later. Failure will happen gradually, too, so there won't be clear warning signs once it starts.
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  10. #190
    Join Date
    8th July 2018 - 07:46
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    Ducati ST2 2003
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    whakatane
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    19
    Hi Thanks for the update

    I put the MBP retainers in my ST2 about 5000 km ago, havent checked the clearances yet but likely i will have the time in the next few weeks given as work isn't looking like happening much in the near future.

    I got my closers down to zero or basically zero, once you get below 1.5 thou it really doesn't become measurable but with the belt off you can spin the cam and also rotate the closer until you get no binding, you can feel the binding easily and in reality you are only doing 4 closers on a 2v so can take your time.
    I treat anything less than 1.5 thou and no binding as basically zero.

    I have a sheet of glass with 400grit black wet and dry that i use with WD40 for doing shims, it works great, you could use a coarser paper but i prefer the fine paper and a little more time. Be sure to wash the grit off the shim with brakeclean twice before remeasuring and also before putting back in the engine.

    I set the openers to around the minimum clearance but never less than minimum on an opener.(Closers gaps get BIGGER with heat, Openers get SMALLER)

    I have done another set of clerances on a 1098 also fitted with MBP retainers and they really make the job easier, they dont stick in the valves like half rings and you dont have to figure out which is the right way up (removed half rings have a tiny wear gap where they tap the shim and need to be put back in the same way)

    Just make sure you plug the oil drain holes in the head, those corded ear plugs work wonders, the cord makes sure you cannot leave them in the motor.

    My IDLE is much better, thats the only noticable differerence, when i am riding in 50k areas. Maybe a bit less rattle but hard to tell with a dry clutch

    Let me know if you need 2V shims. I have a MBP kit here.

    Noel

  11. #191
    Join Date
    28th January 2015 - 16:17
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    2000 Ducati ST2
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    Hi Noelh,

    Thanks for the offer on the shims - we'll see how things are once the retainers get here. I'm hoping that the problem is the half-rings, not the current shims, but possibly they've been wearing or getting hammered too.

    What you describe is pretty much exactly what I did for the 900SS when I fitted the MBP collets. The collets are everything you say they are. The great thing about the belt system is that it is pretty easy to take the belts off and try camshafts by hand; there can be a very fine line on closer shims, as you say. Good point about closers opening up when engines warm up - the closing clearances are definitely bigger than 1.5 thou cold and yep that could be vacuum leak right there, too.

    I changed out the ignition and fuel pump relays today as well but haven't test ridden yet.

  12. #192
    Join Date
    28th January 2015 - 16:17
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    2000 Ducati ST2
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    I've swapped the MBP collets in (post, ex USA, got here in a week. Impressive). Re-test on clearances shows that opener shims are fine, possibly even a bit on the tight side, but closers have all opened up.

    I'd guess that wear on the valve seat and inner valve face has matched wear on the opening shims, rocker arms, pivot arms, and camshaft. The wear patterns have compensated for each other.

    This has happened in reverse on the closing shims, the wear has added together, so things have opened up. It's not much: as far as I can tell, it's just 0.002" at the most... but I'm seeing closer clearances of 0.004". Fiddly re-shimming is now necessary.

    This time around, instead of locking forceps, I tried using rope fed into the cylinder and a deliberately closed piston to keep valves high. This took a few minutes to set up (and the rope has to be scrupulously clean) but worked very well. Pro mechanics use a threaded fitting and compressed air. Both methods have a massive advantage over the forceps: it's possible to push the closer arm down right to the valve stem seal, making it much easier to remove or fit collets to the valve stem. The rope is also intrinsically safe against a valve dropping into the cylinder.

    I took a set of close-up photos of the old half-rings, for interest's sake. Damage on both sides of the half-rings is visible. There's a flat on the side resting on the closer shim, and an angled mark on the valve stem side. Both contact patches are quite small, which wouldn't have helped.
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