Winter Layup - 1995 Ducati 900 Supersport

[OddDuck]

First steps on a couple of things.

1) Fitting the electronics to drive the carburettor bowl heaters. The little thermostat needs an on-off switch, a fuse, and weather protection. This was a bit of an exercise in just buying an enclosure and trying it for fit, to both the bike and the components mounting on it or in it. It was only $3.50 out of Jaycar, it's not the end of the world if I have to go back for the next size up or down.

It'll go onto the bike. There's a place where it can be tucked out of view inside the side fairing, mounted on the instrument sub-frame side rail, but accessible to a gloved hand for switching on or off.

In this setup, I won't be able to see the relay indicator, the digital display, or access the setpoint buttons. That isn't really a problem though... I'll set operating temperature once, then never worry about it again. All I really need to know is how long to run the heaters before hitting the starter button.

2) fitting the heaters and temperature sensor to the carburettor bowls. Should be easy, could be easy, so far it's fighting me. I tried making a clamp-on metal block, but it's clunky at best and it won't transmit heat well without thermal adhesive or similar. I'll revert to sticking the heaters in the idle mix adjust screw holes, with provision for easy removal, and find a place to fit the sensor. Somehow.

3) thermal adhesive. This stuff might make life a bit easier: it's two-part epoxy, but with thermal conductivity like heatsink paste.

The stuff I've ordered is supported by its parent company with online datasheets, including good info like glass transition temperature, service temperature limits, and susceptibility to solvents like petrol. So far it checks out... here's the page:

https://www.atomadhesives.com/AA-SUP...Epoxy-Adhesive

I ordered a pack through Amazon. It's a pain having to wait, but I'd tried local supply (Jaycar) and all they had was thermal plaster. I don't think it'll survive. Vibration, heat, thermal expansion, and petrol don't make an easy environment for this stuff.

[OddDuck]

I finally took a few hours and went through the numbers on latent heat of vaporisation for various different temperatures. Assumptions:

5000 RPM
100% volumetric efficiency
Throttle position doesn't matter
Petrol's relative density at 20 C is 0.72 (relative to water)
Petrol's change in mass is 0.7 g / litre degree C
Humidity irrelevant for this.

So, the equation for heat of vaporisation sums up as:

L = ¹/_d x (194.4 - 0.162 x T)

where

L = heat of vaporisation, in ^kcal / _kg
d = relative density, dimensionless
T = temperature, degrees C.

The density of petrol changes with temperature of course. If we start with petrol @ 20 C, then:

5 C: 730.5 ^kg / _m3
10 C: 727 ^kg / _m3
20 C: 720 ^kg / _m3
30 C: 713 ^kg / _m3

So, factoring that density change into the heat of vaporisation, and working out L:

5 C: 265 ^kcal / _kg
10 C: 265.2 ^kcal / _kg
20 C: 265.5 ^kcal / _kg
30 C: 265.8 ^kcal / _kg

Basically the heat of vaporisation is insensitive to temperature. This was a surprise, but maybe that's why petrol is widely used as a fuel, it's forgiving to work with.

Anyway, carrying on to work out heat absorbed from vaporisation. I assumed that tuning had been set at 20 C, with a 1:15 fuel-air ratio, and that the volume of fuel subsequently was constant against temperature. The density of fuel, like the density of air, would change with temperature, hence ratio changes due to temperature. 5000 RPM, 900 cc, 1 atm, 100% volumetric efficiency... here's my first go at a table:

Temperature (C)	5	10	20	30
Density Air kg/m3	1.269	1.247	1.204	1.165
Mass Air (g)	95.175	93.525	90.300	87.375
Mass Fuel (g)	6.11	6.08	6.02	5.96
L kcal/kg	265.0	265.2	265.5	265.8
Heat Absorbed (Watts)	386.9	385.3	382.0	378.5

So the wattage required to evaporate the fuel does increase slightly as things get colder, but it's not a big change.

At this point I realised something... before the fuel can evaporate, it has to be brought to evaporation temperature. Whatever that is. There's a range of volatiles in petrol and as such there's a wide band of boiling points. These are also affected by pressure.

An issue with volatiles like petrol is something called partial pressures. A bit of petrol, at almost any practical temperature / pressure, will evaporate until equilibrium is reached between vapour and liquid. I've decided in the interests of sanity to ignore this, assuming flow rates through the carburettors are high enough that bulk evaporation only needs to be addressed. The other issue is the pressure drop in the carburettor bowl. It'll be running below 1 atm in there, and that means the boiling point is lowered.

So... further big assumption... petrol (generally) starts evaporating at 38 C and reaches final boiling point at 205 C, at 1 atm pressure. I'll assume that an ideal base temperature for petrol to be at, in the carb bowl, is 30 C.

Droplets sprayed cold into incoming air will have to be raised to 30 C before they can evaporate. This heating will happen under compression, even in a cold engine. The incoming air charge will get heated purely by compressing it. However it will take time, not all the fuel will convert to vapour, combustion will be messy at best... what if the fuel is preheated, prior to the carburettor, and what wattage is needed to do that?

For the same set of conditions as above:

5 C: 337 watts
10 C: 270 watts
20 C: 135 watts
30 C: nil, it's already there

I don't think that this will affect carburettor icing, though. That's purely down to water vapour, air temperature, lowered pressure through the carb venturi, and the heat of evaporation of petrol. It's a widely known issue in light aviation, with a lot of charts available showing icing conditions and when to apply carb heat. It looks like heating the entire carburettor is on the only way to solve icing. If anything, pre-heating inlet fuel but leaving the carb cold might actually make icing worse, since the petrol will evaporate closer to the carb throat instead of staying in droplet form further down the inlet manifold.

Pre-heating inlet fuel... I think any advantage here is in engine starting and cold-engine rideability. It's going to adversely affect carburettor tuning vs temperature, by reducing density of the fuel against cold air, and there may be issues with reducing internal cooling in the cylinder and head during the induction / compression strokes. I'll have to do some further reading and see what's already been done.

[OddDuck]

I had a couple of orders arrive, concerning tools for work on the valve shims.

The first was this odd set of plastic pliers:

http://www.regal.co.nz/category.php?sub_id=663

The idea was that they're non-marking and they lock. Ideally I'd like rubber-jawed, adjustable position vicegrips with a 45 degree gooseneck in the jaws, with a slender nose as well... but nobody makes these. Fine. We'll give these a go.

They do actually work - perhaps better with some heatshrink over the jaws so that they grip better - but once filed at an angle, they'll hold the valve stem without damaging the valve guide seal. They don't hold particularly strongly so there may be a couple of repositions and haulings up of the valve, however it's a lot better than mechanic's magnetic pick-up tools and lots of fiddling. Or cable ties and side cutters with bits of loose plastic pinging around, if I don't cut the seals into the bargain.

The second item was this:

http://emsduc.com/product/rocker-holder-tool-2v-7mm/

I saw the photographs and thought I could knock this up in half an hour out of a piece of barstock. Then I bought it anyway. I'm glad I did, this wee tool is a gem and I sincerely wish I had this years ago.

It does raise questions though... is there a difference in shim clearance measurements when bodging with a screwdriver vs using this?

This thing is highly controllable. It's easy to feel the slack in the closer arm and it's easy to be consistent. That can't be said for jabbing with a screwdriver. I also found that the valve clearance measurements I took at the last service interval were questionable to the point where the replacement shims I had also ordered weren't of use.

Replacement closer shims caused engine lockups (this is why we always turn the engine over by hand with an engine rotation tool, straight off the crankshaft), and replacement opener shims were simply too large and would have left the valve off its seat. Something's going on. Hmm. For now I've put covers back on and left the engine as is; I'll check again at the next 3,000 mile interval.

[OddDuck]

The reason it's been so quiet on this thread over the last week or so is me trying to actually concept, design, and make the attachments needed for the cold-start system. It's been fairly involved.

Quick recap: I think that pre-heating the petrol, directly in the carburettor bowl, is a valid alternative to a choke for enrichening the mixture during cold starting.

The trouble is getting a heating element into place and then controlling it. We really don't want to boil the petrol off or worse, damage rubber seals. The carb bowl, as is, doesn't give many options for placement of either heater or temperature sensor. After several full nights considering what to do, I finally decided to bolt an attachment plate on, carrying the temperature sensor for the control thermostat, and providing mechanical retention of the heater element itself. This was to be one of the 40 W cartridge heaters (from the 3D plastic printing industry), directly inserted into the bowl well for the idle mixture adjustment screw.

The heater had to go straight into the carb bowl, somehow. Heating a clamp-on plate up was simply never going to work; the interface between two different bits of metal was always going to be too much of a heat barrier. This oval 6x7 well was the only place suitable for the heater.

So, holding the heater on... I thought about wire clips, springs etc, and finally realised that the only solution that I can count on is a bolted-on plate, supporting the heater from below. There's simply too much vibration for anything else to work.

It's the same for the sensor. It's got to be secured. Glue, spring clips, clamps etc will fail, after a while. It's got to be bulletproof. The last thing I want to be doing is breaking tools out while on tour.

I'd like to model and cast a replacement carburettor bowl, carrying re-entrant wells for both heater and sensor, these re-entrant wells carrying circlip grooves or similar. Failing that, I'd like to machine bowls up out of billet. Neither is an option right now unfortunately, so a bolt-on plate it is... this can be done with suitable plate stock metal, a drill press, a bench vise, and hand tools. You don't need a foundry, dedicated moulds, or CNC machine tools to make this happen.

So, I got the carburettor bowls off the bike, got the verniers out, measured up, and had the first go at it. I'll quickly mention methods, in case this is useful for someone else out there.

Marking out was done by drafting up in a CAD/CAM program and printing out at 1:1 scale, then sticking the printout directly to the metal with double-sided tape. This lets me quickly centerpunch holes without fiddling with ruler and set square, also it keeps a limit on inaccuracies. This isn't better than +/- 0.25 mm, but for this it doesn't have to be.

Drilling the big 20mm holes needed to clear the carburettor bowl drains was done with a step drill. These are normally intended for sheet metal or plastic; in this case, I went straight though 6mm plate with a 4-12, then a 10-20 mm step drill in one setup under the drill press. It actually works if swarf is cleared and lots of cutting fluid is used. The final 20mm diameter is best done by slightly extending the drill in the chuck, not (as I did) turning the work over.

Cutting slots was done by drilling a hole and then filing with a chainsaw file. These are great little things - constant diameter round files. I've found them much more useful than standard, tapered round files.

Cutting from the plate itself: I'd centerpunched the outlines, so after the printout failed under cutting fluid and abuse, I still had the outline to work to. This was simple work with hacksaw and file.

Fitting the plate to the carburettors: in the electronics industry, they use a lot of PCB spacers. These are useful fasteners for this kind of work. It turns out that if I have 14mm spacers at the rear, 32mm spacers at the front, then I'm on the same plane as the machined flat carrying the carburettor bowl drain. These spacers had to be cut to length and then squared up. Lacking a lathe (I'd really like one someday) a makeshift technique is to roughly length them with a hacksaw, fit them into a drill and present them to a grinding wheel, square on. This trues them up and lengths them quite nicely and controllably, albeit with a few stop-starts and checks with verniers.

The sensor retainer plate: this was drilled locked into the master plate. No tool more sophisticated than a manual drill press was needed. That said, these retainers are individual to their master plates, they're not interchangeable.

I have no idea yet if all this actually works. I'll have to remove the carburettors from the bike and get them onto the bench to test fit, file holes, and fit properly... or redesign and remake where necessary.

[pete376403]

If Bert Munro rode a Ducati, this is how he would have done it.

Files, hand drills and the odd thermal camera.

[OddDuck]

"blush"

High praise indeed. Haven't been trying to file camshafts out of tractor axles yet though...

I did Gold Ride Forever on the weekend, then took Anzac Day to go out and have a first try at practising some new skills.

I've been learning to ride ad hoc. It took doing a course to really highlight the gaps in what I'm doing; it's very difficult to see what's missing. The old saying about getting to a level and then staying there has applied for some time and it's good to make progress.

Highlights (for me):

- Trail braking (already proved its worth in a tight corner)
- Using rear brake only when at low speed, pulling up, parking etc
- Looking through corners to the vanishing point, eyes up and on the horizon
- Corner to the longest possible visibility instead of race apexing
- Clutchless shifting. This probably wasn't part of the course, it sort of happened incidentally... for me this was huge. I've heard about it but it wasn't until someone else was doing it in front of me that it 'clicked', so to speak.

That's a fraction of what was covered. It was a good day out, so was the day of trying to ride in a new way.

[Voltaire]

"blush"

High praise indeed. Haven't been trying to file camshafts out of tractor axles yet though...

I did Gold Ride Forever on the weekend, then took Anzac Day to go out and have a first try at practising some new skills.

I've been learning to ride ad hoc. It took doing a course to really highlight the gaps in what I'm doing; it's very difficult to see what's missing. The old saying about getting to a level and then staying there has applied for some time and it's good to make progress.

Highlights (for me):

- Trail braking (already proved its worth in a tight corner)
- Using rear brake only when at low speed, pulling up, parking etc
- Looking through corners to the vanishing point, eyes up and on the horizon
- Corner to the longest possible visibility instead of race apexing
- Clutchless shifting. This probably wasn't part of the course, it sort of happened incidentally... for me this was huge. I've heard about it but it wasn't until someone else was doing it in front of me that it 'clicked', so to speak.

That's a fraction of what was covered. It was a good day out, so was the day of trying to ride in a new way.

Out of interest what are the benefits of clutchless gearchanges?
I know they do it on racetracks but I've never been keen on my airhead BMW racer having seen the inside of them.
Its enough for me locking the rear dropping into second...
Only time I ever used it was when the clutch cable broke and had to sync the gears before easing the lever thru.

[jafagsx250]

It's faster at the drags but off the top of my head there doesn't seem to be that many benefits

Sent from my GT-I9506 using Tapatalk

[OddDuck]

Yep agreed, way faster at the drags (and presumably blipping down while approaching corners). It's a valuable track skill. No wonder track riders will buy quickshift kits.

In terms of safety, about the only justification I can see is minimising the time that the engine isn't engaged with the rear wheel. The fastest that I can do a clutched shift is maybe half a second, and that's risking skidding the back wheel if I'm engine braking. Clutchless, if done right, there'd be potential for a false neutral for a fraction of that time.

Unfortunately (speaking authoritatively here after one day's riding practice) you've got to get the matching between rear wheel and engine right otherwise the gearbox locks and won't shift. In a panic situation it might be very easy to get locked into the wrong gear.

The other use I can see for learning this skill is in the case of a stuffed clutch actuator. Maybe the bike's had a fall and broken the lever off, maybe the hose or cable has failed, or the seals on the slave piston have gone... you might have to get a bike home without much in the way of clutch usage.

I'll keep practicing and see. In the meantime I want to read up on what this does to the lifetime of a gearbox - I made some pretty choppy changes yesterday and had the bike lurching or diving a couple of times, that sort of thing can't be good.

[jafagsx250]

I am pretty curious about how bad downshift are clutch less. It doesn't seem so bad up shifting but I pretty much always use the clutch to down shift.

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[OddDuck]

I had less trouble with downshifting than going up. A little blip on the throttle, shift, done.

Seems the trick is to get the torque transmitted to the rear wheel as close to zero as possible. Early days yet though.

[Voltaire]

I did a Honda riding school once in the UK and I remember one line " use the brakes for slowing down not the gearbox as brake pads are cheap to replace

gearboxes less so"

I can see the benefit of any time saving ideas when racing but when you have to dismantle your Bevel Drive Ducati because it jumps out of 1st dues to worn dogs

you tend to use the clutch. Modern gearboxes are probably stronger.

My stock carbs on the 900 SL are leaking, where do I get that float and valve assembly from locally?

You mentioned BMW airheads earlier....far easier to do the carbs on them

[OddDuck]

Apologies for the delay in replying.

Stock carbs bits are easy - dealer network or online through Stein Dinse. I'd go dealer network if possible, I had bits ex Aus in about a week when I replaced emulsion tubes.

[OddDuck]

Finally had a moment to get back into it, with several issues wanting attention. Last night I had a look at the weak front headlight - these bikes are notorious for dim lights.

It's been like this since I've had it. It's been liveable until a recent ride involved crossing the Rimutaka Hill after dark. Late, tired, oncoming cars with dazzling headlights... not good. The headlight's actually OK if my eyes have adjusted to it, the issue is how bright everyone else's lights have become.

The first thing I tried was changing the bulb for something billed as 30% brighter. The two photos of the bike lighting up the garage door are before and after, with the camera shooting on full manual and the exact same exposure settings in terms of shutter and aperture - in short you can see the difference.

There is actually 30% more light. That shows up on the exposure histogram. The trouble is that it doesn't look like much at all to the eye; cameras see light in terms of double or half and I think the human eye works on similar scales.

Much earlier I'd measured voltage at the headlight bulb and found it wanting. Not re-measuring (I should have) I took the handlebar switch block off, with a view to getting into the contacts and giving them a clean. Basically, for anyone else out there contemplating this, the headlight / indicator / high beam switch block isn't serviceable, as far as I can tell. It's snap-together construction which doesn't come apart again. Some of the plastic seemed to have the beginnings of cracking, so I decided not to risk forcing anything.

It also seems to have been designed right. The photos don't show this as clearly as I'd like, but a couple of the contacts for the headlight are visible in one frame, covered by the switch mechanism in the next. These are sliding contacts, not press-togethers. They get wiped clean every time the switch is used.

The logical next step to take would be to trace wiring and check contact resistances via multimeter, but the connector block showed clear traces of corrosion on some of the pins. To my mind, that's far more likely to be a problem. Metal oxide is a very good electrical insulator, even in thicknesses of microns. The check is to get some dielectric grease (not conductive, not inside a multipole connector block) and make-and-break the connector a few times to wipe the pins, then try the headlight again.

A last note about checking resistances with a multimeter... I'd read somewhere that the only real check in a wiring loom is to power it up and measure voltage drops across runs of wire, across switches or connectors, etc. The reason for this is current: under power, the headlight draws 55 / 60 watts, at 12V. That's 4.6 amps under normal loading. A multimeter's sensing current for ohms would be in the milliamps. A thread of metal holding a wire together might test alright, under milliamps; it'd be a very different story under nearly 5 amps.

The amperage also highlights any defects in connectors. There's heat damage on one pin of the old headlight bulb. I'll have to get the thermal imager out again and have a look at this connector, with the headlight running.

[OddDuck]

Had a look with the thermal imager tonight, after reassembling the switch block to the bike and pulling the headlight assembly off the front so that terminal connections to the rear of the main bulb could be seen.

A couple of surprises followed. The bulb itself is the main heat source, the terminal and wiring was fine... and there's a pretty obvious hotspot at the main fuses. The wiring's possibly undersized, but it's very clear that there's a high resistance spot at the push-on connectors to the two main fuses. The confusing photo of the wires is of the fuse box underside, showing the leads into the fuses. There are two shots, one with main headlight on, one with the headlight off - the second pair of wires are running cooler with the headlight off.

I tried pulling the 15A fuse and having a look at the blades - one was a bit oxidised, but nothing too bad. The headlight switch and switch block connector didn't show up as anything special on the thermal imager, although I didn't run the ignition for long - the AFR sensor doesn't like being powered up with the engine off for too long.

I re-shot the headlight with the same camera settings as before, a quick test to see if fiddling with fuses or the block connector had helped. It had, a very little, but it's not significant enough to be definite.