Winter Layup - 1995 Ducati 900 Supersport

[OddDuck]

I think you should make your battery box in steel as you are then use it as a mould to remake it in fibreglass.

It would be really interesting to have a play with fibreglass, I've never used that material before, but I'm running tight on time. Need the bike ready and running in two and a half weeks... it'll have to be this, welded up and painted.

I weighed the OEM airbox / battery box / coil mount assembly last night and was surprised to find it coming in at 1670 g. That's with the lid opened up and snorkels removed, rubber trumpets included in the box. So there's not that much change in weight anyway.

[OddDuck]

Folding the plate carrying the coils and CDIs.

The steel I've got is 3.5 mm thick, way too solid for the little mechanic's vise I've got on the bench. I carved out a channel with a 2mm cut-off disc down to roughly a third of the original thickness, then folded via G-clamps and crescent wrenches (for extra leverage).

It worked out very nicely - no curves or waves in the plate outside the bend radius. I'll have to weld the channels closed if I want to restore the original strength.

[OddDuck]

Welding the box together.

Welder's magnets are really good to have - the ones pictured can be set to any angle and also can close a 90 degree angle around the outside, very useful for a box like this since it's too small to fit normal one-piece magnets on the inside.

I tack welded, then started running the seams. Compared to the frame welding earlier, it's been an absolute doddle. Straight lines, easy access, not even any need for filler rod most of the time. Melting the parent material together is working fine. Something that helped a lot was using the welding table surface as a guide for the torch.

A while ago I'd been told about the value of good welding helmets, after today I believe it (still welding with a cheapie for now). The ability to see precisely what's happening is pretty much essential, as soon as I'm guessing then the weld's turning into a mess.

The two smaller mounting tabs were the only welds that needed filler rod. I'd left them undrilled deliberately, there isn't much margin for error with these and I'll have to mark out by fitting to the frame.

[OddDuck]

Threaded spigots have to be welded on in a few points too.

A mistake I made with the box was not wiping the panel edges down with a new rag and acetone. I'd used the usual water-soluble degreaser, but had a few spots of porosity come up in the weld from residual oil. Didn't want it to happen twice, so went for immersion washing of the spigots first, then positioned these and welded.

A couple of notes... the thermal mass of the spigot is much less than that of the plate it's welded to. It's very easy to melt the spigot rim back without connecting to the material underneath. I found that making a puddle in the plate, then walking it up to the spigot edge, tended to work best.

I made a mistake with one of the spigots carrying the coil / CDI bracket... I left the M6 cap screws I'd used for positioning and clamping during tack welding in place during the main welding.

Not a good idea. Either I managed to collapse the spigot wall a bit, or I bent the screw, or something else happened... but it wouldn't come out after the lot had cooled down. I tried forcing it and the head snapped off, leaving a few spigot threads clear and the rest of the screw jammed in. This was fixed by using the accessible threads as a guide for a 5.0 mm drill and drilling the body of the screw out, then chasing the threads with an M6 bottoming tap got the rest of it out. I've probably lost the crests off a few threads doing that, but it looks serviceable.

[OddDuck]

The box needs to be stabilised against rocking forward / back on its two side mounts.

One idea I'd had was to clamp to the bar I've installed across the top frame rails, for this I'd need a split clamp welded to a bracket to connect to the box.

Ducati use a technique of fixing threaded bungs to the frame via a weld bead. I gave this a go and found that it can be done relatively easily. Unfortunately the results aren't exactly gorgeous... a shame really. I know that temporary solutions have a habit of becoming permanent, but I'll probably have to go with this for now.

[OddDuck]

Box now in position in frame, anti-rocking bracket yet to be made.

[OddDuck]

I really wasn't happy with the split clamp, so remade it, this time from a decent piece of stock metal and a couple of cut-down M12 bolts. The hole was initially drilled with a 25mm holesaw, marked out to final size using a socket with right outer diameter, and then filed.

A couple of notes from the day... I did some reading about alternatives to machining up spigots (or whatever the things I've been making should be called). A lot of guys simply weld commercial nuts down to plates, but that has issues with the plating giving off fumes when it's welded. Galvanising is nasty, so is the yellow stuff seen on the high-tensile fasteners. Grind or blast first, basically. Stainless can be used but it's a third the strength of steel and apparently there are also issues with hexavalent chromium.

Weld nuts exist commercially. They're basically standard black steel hex nuts with a locating spigot on one side. The idea is to drill a hole for the spigot, fit the nut, then spot or mig weld it into place. Quick, easy, good. The trouble is getting them at short notice and in small quantities... I've never seen these on the shelf anywhere, which is kind of odd thinking about the numbers of people out there making stuff in garages.

Anyway, carrying on... Anti-rocking bracket now welded up and good to clean up and paint. It's been tried for fit and goes on OK, although it was fussy to make. If this design doesn't work out, it's still possible to rebuild this component and use the existing forward airbox mounts on the frame, with a new bracket design.

[OddDuck]

Had a first go at vacuum forming plastic today. I want a mount for the wideband AFR sensor's gauge.

Failed, but learned a bit... the technique is simple enough, it's basically one-sided moulding of plastic sheet. Heat sheet up in a frame, stretch it over a positive former (that's the mould), then use vacuum to suck the hot plastic down over the former. The professional machines sometimes bubble the material with positive pressure first, to give more uniform wall thicknesses after forming.

I went wrong in at least two areas: the plastic chosen for a first go, and the frame to hold the sheet with. I bought a polypropylene box for the princely sum of $6. It wasn't much work to cut the plain base out of it. Unfortunately the PP is a great material for injection moulding, which is why the hardware shop had boxes made of the stuff everywhere, but a terrible material for vacuum forming. It buckles, also apparently it goes soft one moment and then promptly melts the next. Very tight temperature control is needed. All I've got is a standard domestic oven. It's simply not happening with PP here.

The forming frames didn't hold up to the buckling of the plastic - quite a few of the screws ripped out. A couple of the bits of wood also buckled, and of course the paint was an issue in the hot oven. I'd seen it, thought I'd give it a go anyway, but it really wasn't a good idea to put painted wood into an oven at that temperature. Oops.

The last note from the day is the amount of vacuum used by the commercial machines: they're pulling nearly 27 inches Hg. I've got a standard domestic vacuum cleaner, it's pulling a fraction of that, but I'll have to see how I go with what I've got.

I've found an ABS tray via Trademe and will try again with that, in the meantime I'll have to make new forming frames.

[OddDuck]

While painting the new battery box and bracket, I got onto preparing the exhaust pipes for the new O2 sensor threaded bosses. I have to drill and weld, and of course they've got coking / carbon on the inside. Best to clean before welding. One of the weld zones is directly accessible (on the short 90" pipe pictured), the other is around a bend and some distance down the pipe, just before the cross.

An idea I'd been toying with for a while was to shove in some gravel, pour in some degreaser, cork all open ends and then simply shake the thing. Gave it a try today. It works, albeit slowly and with some labour. It's very much a method of diminishing returns, so I've got near enough and stopped, instead of trying for 100% clean metal. A look in the screw port next to the weld zone showed clean metal inside (it was a bit difficult to photograph properly). I'll take another look once I've got the holes for the bosses drilled.

[OddDuck]

New battery box and bracket now painted and installed.

One of the issues with steel construction (instead of fibreglass or plastic) is that I'm going to have to be very careful with cable routing and edges... if insulation gets cut or worn through then I'll start having nasty short circuits. Some stick-on cable mounting feet should help here.

I've started preparation for welding the O2 sensor into the header pipes. The very short drill pictured is a center drill, normally used on a lathe - I've found these quite useful as pilot / guide drills for general work. There was no issue using a 16mm holesaw to make the entry hole for the O2 sensor. The weld-in bungs I'd bought via Amazon and YouPost had to be filed slightly to match the curve of the exhaust headers.

The earlier attempt at cleaning with gravel can be seen in one of the pictures - it's blue inside because I had to use a LED torch to light it up. Basically the carbon's gone, but the surface oxides are still there.

[OddDuck]

Welding the bungs to the exhaust headers.

I did a lot of reading through the week about welding stainless and decided to back purge the welds - to have both sides of the weld gas shielded. The reason for this was to try to avoid embrittlement / corrosion problems later on. The stainless steel gets its corrosion resistance from a very thin layer of chromium oxide, and modifications to this oxide layer (temper zone from welding, black 'sugar' on the reverse face etc) destroy its corrosion resistance.

The gas shielding is a simple idea: run a second line from the regulator to the work and use bungs / tape / plugs / whatever to control the gas flow through the inside of the workpiece. It's important to leave open gas escape ports, so the weld doesn't pressurise. A vertical column flowmeter, with a needle valve, manages the gas flow. I managed to borrow a scientific O2 bench meter from work and checked how quickly the work purged - it turned out that, even at the smallest measurable flow rate, the smaller pipe cleared to less than 0.1% oxygen in roughly ten seconds. The larger header assembly took a bit longer - roughly 30 seconds - but cleared readily. This was at flowrates of around 1 ltr / minute. The needle valve doesn't turn on / off with the torch, so there's a lot of manual on-off while fiddling with setups.

Material compatibility is important - the wrong grade of filler rod could cause problems later on. I know the headers are non-magnetic stainless but don't know which alloy. Same thing for the bungs. I've taken the guess that they're all 304 and welded with 316 filler rod. By far the most common alloy used in exhaust systems is 304, and the common wisdom on the welding forums is that going up a grade for filler rod is perfectly fine. It's all guesswork though, only longterm service will show if this holds up.

I used a pair of M18 x 1.5 threaded plugs to seal the bungs, while welding. Unfortunately one of the threads galled on the way out, balled, and tore itself to shreds inside the bung. It had been a bit notchy going in. Should have used high-temp stainless anti-seize... It looks like the bung threads are mostly still OK, but after failing to pick the embedded threads out with a scriber, it looks like I'll have to invest in a tap to clean it up. The weld bungs have a tendency to collapse slightly under welding anyway, running a tap through them again after welding is probably a good idea in general.

The welds themselves look OK. I'm a fair way off being able to produce welds with stacked pennies, but for this they'll do.

[OddDuck]

I had success with plastic vacuum forming today - the mounting for the AFR gauge is now in place.

Setup was as previous try - vacuum box, frames, domestic vacuum cleaner, domestic oven. The plastic was some ABS, sourced as camping food trays off Trademe and cut down to sheets. The revised frames were one-piece aluminium sheets, about 2mm thick each. I didn't have a way to make the usual bulldog clips work (easy, cheap, good - shame really) so made spring compressors via long countersunk M4 screws and coil springs.

As to the forming itself... ABS is supposed to be easy to handle, with a wide forming range, but I struggled. I'd say, based on this experience, that about 2mm is really the limit for the home worker with this gear. I was using material that was roughly 3mm thick and could only just get it to form. A domestic fan-bake oven struggled with the control and stability needed. Bits of the sheet showed overheat damage despite the material not having softened all the way through, at the same time the vacuum didn't have the grunt to pull the plastic into the corners properly. There are also significant wrinkles, but I'm not sure if that'd get better with a thinner sheet.

The other thing is the smoke... ohh boy. One of these days I'm finally going to learn about bits of wood and ovens. If you're going to do this, don't do what I did and use 2x4's to space the frames upward from the nearest wire-frame oven drawer. The pine wood will boil out sap and smoke very badly (especially if it's off the garage floor and has been getting oil spilled on it). Spacers are needed, the ABS sheet will sag downwards when it's ready to go, and for this form I saw it move by 30 mm. The frames have to seal to the vacuum box, that usually means that they're flat, so something is going to have to hold them up a bit from the oven's trays. Just don't use wood. Aside from the oil smoking up, I saw the wood come out of the oven with the beginnings of charring. This happened at around 160 C, it didn't take anywere near as much heat as I would have expected.

I'm not sure how much smoke came off the plastic itself. I think most of it was the wood, but at the heat-damage stage, it's possible that the plastic smoked too. I wouldn't do this in my food oven again, put it that way... it might pass for a one-off but that'd be about it. Looks like there's very good reason that commercial vacuum forming machines exist.

That done (and windows opened) I found that the formed sheet came out of the frames easily, but the mould took some persuading. I'd made this in four layers of MDF scrounged from scrap kitchen bench board, with quite steep angles. Trying to pull the thing in one go didn't work but taking it out layer by layer did.

From there it was a simple job of trimming it via drill, wood saw, hacksaw and files. It took some file-and-fit to get it into place, but the gauge fitted in without problems. Clearance to brake lines on full steering lock is very tight but it works.

The boxy grid thing on the warning lights is an earlier modification. Ducati warning lights are notorious for going invisible in direct sunlight. The grid was made via 3D printing and provides shade at most angles so that I can still see what's going on, it works almost all of the time except for when the sun angle is directly over my shoulder.

[OddDuck]

Connecting the AFR gauge to power.

This gave me a bit of trouble... the usual story with an accessory is that mostly they can be connected on top of the battery terminals. If they have to be switched through the ignition key, it's just a matter of finding a positive line and splicing into that.

The gauge draws 1.3 amps and requires a switched, 10 A fused supply. It'd be easy to cause problems by splicing in at random and causing an overload. I've spent a few hours going through the wiring diagram, trying to understand how the loom works.

The bike's main fuse box divides the wiring into five areas:

30A - main battery line, starter motor and charging circuitry
15A - ignition circuitry, fuel pump
15A - headlight, high / low beam
7.5A - indicators, warning lights
7.5A - horn, brake lights

I've added up the electrical loads already present on the two 7.5A fuses and found that the last one (horn, brake lights) will draw 3A in the worst case operating condition. That leaves a fairly generous 4A operating ceiling for accessories. In the event of a problem causing a blown fuse, I'll lose the horn and the brake lights, but that's all... the bike will still get me home.

The horn also turned out to be running 12V full time - it's switched through the ground line, presumably to simplify the wiring. This means that it's a good place to tap into for the switched positive supply, although I'll have to be sure of which spade lug to connect to. The ground connection can be achieved by connecting a lead to the front subframe grounding point.

The best bit about all of this is that connection can be achieved without cutting or soldering - I can use an eyelet for the ground and a bridged spade connector for the positive, so I don't have to hack up the loom or use a soldering iron to change anything later. I've chosen to use a 2-way connector rather than direct leads, so the connector can live on the bike permanently and I can tap in as and when I need the supply in future.

The AFR gauge is intended to go on for carburettor tuning and maybe a couple of decent runs to check engine behaviour, but once tuning is done I suspect it'll just turn into a distraction. I'm also keen to use it on other vehicles. It'll be good to keep the option of removing it easily.

The M18 x 1.5 tap arrived today - I got the exhaust bung cleaned out with a makeshift tap handle (via the socket set) and a plug fitted. Then I sorted out the last connections in the wiring and refitted the fuel tank.

[OddDuck]

Pulled the plugs, set kill switch to off, and cranked the starter motor until the oil level stabilised and the oil pressure warning light went out. Then I refitted the plugs and HT leads, put some fresh petrol in the tank and gave it a go.

Some cranking, one backfire, and then she ran. Idle's going fine. AFR gauge indicates 11, header pipes are getting stinking hot, so I think some rough driveway tuning is a good idea before going anywhere.

[OddDuck]

A bit of have-a-go carbie tuning... starting with removal of my homemade spacer plates for the inlet trumpets. These were needed for the old airbox - the trumpets weren't quite long enough as supplied, the airbox couldn't be sealed properly and there was a problem with road grit getting into the carburettor bowls and jamming up the needle valves. This caused the engine to fill up with petrol overnight, flooding the exhaust sytem as well. I had to throw the oil away. This is why proper sealing of airbox / inlet system is essential for carburetted bikes. It's not for vacuum leaks (not before the throttle plate or butterfly, anyway), it's against the dirt. Switching to pod filters means the plates and gaskets can go into honorable retirement.

My first go at tuning was simple enough: set the slow fuel screws to 1 turn, turn out the slow air screws to 2 turns. The AFR gauge is now reading about 12 - 13 between idle and 1/8th throttle, so I'll have to go in again. I don't want to go higher on the throttle with a free-revving and just rebuilt engine, though - until I'm on the road again, the higher throttle settings will have to stay as they are.