....goes the old weight-loss mantra. Yup, it was time for the 851 to take out a Jenny Craig membership.
I'd always known the ol' girl could never compete with the IL4's for outright hp, but a light, good handling, hard braking bike might just be an interesting alternative approach to a half decent laptime. So even as version 1.0 came together, ideas were forming about how version 2.0 might look.
One upgrade that was almost forced on me was replacing the alloy tank. The thing had a couple of small weeps at a seam (repaired) which I initially wasn't too worried about, but another bad leak from a different area during the first dyno tune (directly over the vertical exhaust manifold) was a real concern. From sitting on the shelf for a few years it seems condensation had settled at the low points where corrosion got down to business.
The quandary is that a replacement is serious coin, if you can find a good one.
I was just starting to explore tank sealing options (would they work on a corroded aluminium surface?) when Termignoni (the Roman god of racing, remember) smiled on me: a used carbon Corsa tank cropped up. It was complete with hard to find fittings, in great condition, for the same money as an alloy unit: come to Papa you beautiful thing! (Thanks Mathias)
Here it is fitted to the seller's bike (very cool, there's a lot going on there), with period correct Raymond Roche era graphics:
Note the quick connect fuel inlet/outlet connections outside the frame rails rather than up under the tank. The Corsa tanks went through several iterations, some similar to OEM, but this unit is the "letterbox" variety, so called for obvious reasons:
Remember me bangin' on about the Corsa air "box" actually being more of a "dish", how it was completely unsealed? Ducati had created this style tank to boost airflow into the airbox, which it did, but if anything it actually hurt hp....I'm guessing due to the classic venturi effect, where air flowing across an orifice (bellmouths) creates a vacuum/lower pressure, without sealing the airbox increasing the air flow only increases the vacuum being created. So that gaping maw ended up covered by a carbon panel, which is secured by those threaded studs.
(note: ram air and even fuel injection for that matter was in its absolute infancy here, this was revolutionary stuff at the time)
Ducati part number, back in the day you could have wandered into a dealer and ordered this tank over the counter...if your pockets were deep enough:
Corsa quick connect fuel fittings below, as used right up until the 996RS. The return fitting incorporates a non-return ("reversion") valve:
These Corsa tank fittings are almost impossible to find, but occasionally replicas pop up:
And you'll need a set of these to connect the fuel lines, which are fairly commonly available and not that expensive (CPC, part #: PLCD17004):
I ummm'd and aaah'd over these. There are also stainless steel versions available, which on the face of it seemed like a good idea....but what happens in a crash? The plastic/acetal fittings would break and hopefully the tank fitting would stay intact/sealed....in the case of the stainless fittings the carbon tank would be the weakest link and the complete connection would be torn out with fuel going everywhere, hence I went for the plastic option. I can only hope I never get to test my theory.
Stand-by for some pic's of the tank installed....
That's all well and good, but where is the ultimate place to lose some weight? Rotating mass has the compound benefit of also reducing gyrospic forces, making the bike easier to turn, hence we are prepared to sacrfice beer money to buy magnesium/carbon wheels. Reducing rotating mass in the engine is more complicated but just as important, meaning less energy is wasted moving heavy internals and allowing more energy to be transmitted to the rear wheel. Light wheels have a greater effect at higher speeds, but lighter engine internals have an effect dependent on RPM rather than road speed.
There is a limit to how light you can go, too light and you're left with a lightswitch power delivery and poor traction, as a few Motogp manufacturers have discovered in recent years. Given my almost stock OEM 851 crank weighed a near metric ton I wasn't in the same county, let alone ballpark, of experiencing that issue.
But not so long ago, and since banned, Motogp factories were experimenting with hollow conrods: the counterweights on the crank balance the conrod/piston mass, reduce conrod weight and you can reduce crankshaft weight. Some of the Motogp manufacturers have gotten the flywheel weight wrong in recent times but this leads into an interesting perspective from Ben Fox, world renowned crankshaft guru operating at the highest levels of AMA/WSBK (note, I've cut down some of the info but these are his words):
"Should I lighten my crank?" Yes, no. Depends on who you talk to.
Let me illustrate something for you: Do you ever remember holding a bicycle wheel in your hands and having your buddy spin it? Remember how hard it was to try and turn the wheel? Remember the opposing forces it put into your hands?
Now picture this, The crankshaft is the spinning "wheel" and the bearings in the engine cases are the "hands", what happens when you lean the bike over in a turn? The crank wants to stay upright. Think about the forces that are being applied to the engine case halves and bearings.
****Benefit #1:
A lighter crank will apply less force into those bearings and engine cases.
Now have you heard of crank whip? This is the flexing of the side counterweights. I really don't think I need to go into much discussion on this one.
****Benefit #2:
Less mass on the counterweights = less whip = less flex in the crank.
I'm not here to argue the fact that a stock crank and stock rods are a bad combination. But the light crank and rods will cater to the people who want something a little more than that, and something that takes stress out of the engine, because they are going to be stressing it more than the average person. And quite honestly that's really what it comes down to in the end. Less stress on internals. Yes there's also the benefits of it spinning up faster and accelerating faster from point to point, but I view it as extra longevity."
Hmmmm, lots to think about there, eh?
Ok, but I'd already had my crank balanced for the lighter Pistal pistons and Pankl Ti rods, I'd fitted an ultra-light Nichols flywheel, I'd added extra frame spars to relieve the pavlova-spec crankcases of as much stress as I could, what more could I do?
I didn't need to power lights, radiator fans etc so why was I running the stock 350w alternator? "Who cares?" I hear you say. Well, the 350w (vs the 280w Corsa alternator) output was achieved by fitting a comparatively heavy set of stator and rotor parts, the race parts being significantly slimmer and lighter. They also happen to be stupid expensive if you can find them.
But through the online Ducati community I'd heard of an interesting inexpensive alternative. So many of the Ducati models share similar architecture, be they 2 valve, 4 valve, carb'd or injected and this played into my hands in the form of a 400SS alternator rotor. Being carb'd and air cooled it didn't have anything like the electrical load of a fuel injected water cooled bike, so the alternator was sized appropriately. Here's my 851 rotor vs the 400SS unit:
With a weight difference of 810gm vs 630gm. That doesn't sound like a huge amount (23% reduction) but would have a decent effect at 10000rpm.
You just have to machine a spacer, or find/buy the Corsa spacer, which I shamelessly copied to the best of my amateur ability:
Spacer fitted against the alloy Nichols flywheel:
And rotor installed:
That's all there is too it, just bolt on the cover from here. The spacer is the awkward part if you don't have access to a lathe, but the rotor itself costs bugger all.
Next up was tackling the ugly/heavy plastic rear undertray. This was actually a lot more faffing around, for arguably less benefit than the above, but needs must as the thing just hurt my eyes.
I'd earlier found a rear carbon undertray, vs the more complicated and vastly more expensive Corsa units incorporating the crankcase breather it was a picture of simplicity:
The carbon unit obviously looks better and is much lighter, 1.3kg vs 475gm, this with the rear guard surgically (hacksaw, bonesaw, same thing) removed from the OEM unit by a previous owner, it must have weighed the better part of 2kg in original form. To be fair it was in an era where proper underseat storage was actually a thing, held a toolkit and supported the ECU/power group etc. Ooooh, that's a point, mounting the ECU......uh oh....
Seeing as Elon Musk had decided to partake in a space race rather than club race a Ducati (still waiting for you to return my calls Elon...) a front mount ECU, twin injector throttle bodies, and associated wiring harness were off the table, so the ECU was staying "in the boot". But that scallop in the new tray made things kinda awkward....and I didn't really want a heap of mounting bolts ruining the clean look of the panel underside.
Some beer fuelled inspiration later and a combination of existing mounts, new brackets and anti-vibration rubbers as stand-offs seemed like a goer.
Brackets made:
ECU mounted, rear rubbers are hot glued to the panel, front rubbers utilise the subframe/panel mounting points:
The rear fuse/relay/power group alloy mounting plate is also a bit of a monstrosity:
And it wasn't difficult to take 300gm's out of it:
After all that I just couldn't bring myself to use the original ridiculously oversize M8 (!!!) "bridge bolts" to remount the power group, so cue more eye of newt toe of frog "alchemy" performed on some alternatives to halve the weight of the originals (25gm saving, lol):
And everything back in it's new/old home:
All up, using a few alloy nuts/bolts/washers I had stashed away, it totals a 1.2kg saving. Nothing revelatory, but I'm trying to justify the effort to myself as most of it is from the back end of a bike that could do with more weight over the front wheel....yeah, I'm not convinced either but at least I don't have to look at that bloody plastic thing!
