S4RS Build

The steering damper parts arrived today and are now mounted on the bike. Both components are machined from 6061 aluminium.

Overall, I am pleased with the result. There are a couple of minor cosmetic blemishes in the finish on the bar clamp, but they do not affect fit or function. I am currently in discussion with the manufacturer to see whether anything can be done about that.

The airbox design is complete and the patterns for the mould are now almost finished. Once I am happy with the patterns, I can move on to making the moulds.

I have now finished the design for the steering damper mount and ordered the parts.

That design has changed a few times along the way, partly because I was not happy with the earlier version, and partly because I needed to adjust the clearances for the finalised tank position and the new handlebars.

I have now started redesigning the airbox. The battery, filters, regulator, solenoid, relays, and everything else all need to live in a very tight space, so it has taken a fair amount of trial and error to get things positioned with enough clearance while still considering installation and maintenance once the bike is assembled.

That has been one of the more awkward parts of the build, as moving one thing tends to force changes to several others. It still needs some refinement, but the design is almost complete.

I have had to redesign the airbox again, as I lost access to the earlier CAD work, so I needed a better way of understanding the geometry under the tank.

I made a simple probing jig so I could map the shape of the tank underside and use that data to locate the 3D scan of the tank underside in relation to the airbox model in CAD. This should let me optimise the airbox for volume while maintaining adequate clearance.

I have refined the design of the subframe, had some parts laser cut, and got them tacked into position.

The final version differs slightly from the earlier mock-up, as the seat mounting required me to use flat stock instead of tube. The tank, seat, and tail can now be positioned repeatably.

I have also remade the white insert piece that will be moulded into the seat. That should help close up the void between the tank and tail.

I have started working through the design of the subframe and mocking it up on the bike. I want it to be minimal and, when complete, look as though it was designed that way from the start.

I started working on the subframe. The old one has now been cut off, so there is no going back.

I had some steel from another project with the same diameter and wall thickness I need. I still need to turn some slugs before I can weld it up, so for now it is only mocked up.

I have revisited the tail unit model, and I think it is getting close to where I want it to be.

The small white part under the seat will probably be moulded into the seat itself and then recovered as though it were part of the seat. That should help close the void between the tank and the tail.

I have also started planning the subframe. I have modelled a gusset with a Ducati logo cut into it that will reinforce the subframe once it has been cut down.

The matt white finish makes it difficult to photograph in a way that really shows the contours properly.

I knew I wanted to make it narrower, as the standard 999 tail is wider than the tank and looks a little unbalanced, perhaps because it is no longer on a fully faired bike.

I have narrowed it down and made a first mock-up so I can get something physically on the bike, as it can be hard to visualise in CAD alone.

I like the side profile and front profile, but from a three-quarter angle it still looks too large to me. I may also need to shorten the Termignoni silencers, which I had hoped to avoid.

At least I now have something in place on the bike that I can take proper measurements from. The next version will not be so flat, I would like to add some feature that ties it to the shape of the tank more.

I have started working on a revised steering damper mount, as I was not very happy with the way the last one looked.

I still need to adjust the model and make sure there will be enough clearance with the new handlebars I have ordered (ProTaper Contour CR High).

The machined flanges / starters for the exhaust have arrived. They do look very good, and I think they were worth the cost.

I have also 3D scanned the 999 tail unit. I do not like how wide it is, so I am going to make it narrower so it sits over the Termignoni silencers better. So now I can continue work on the tail unit, subframe, and exhaust together.

I have started to mock up the exhaust. The plan is to use 2-inch diameter 304 stainless mandrel bends for the headers, and at some point I will need to step up to 2.25-inch for the Termignoni silencers.

The oval exhaust port has been a challenge. I have tried to ovalise the 2-inch mandrel bends, but I have not arrived at a result or method I am happy with. I have tried vices, a hydraulic press with some tooling, heat, and a few other approaches. It is especially tight on the rear cylinder, so there is no room for a straight section, which would be much easier to form.

At the moment I have only mocked up the header runs as far as the point where the Y-merge will be. I have not yet worked out the angle of the merge.

Because of that, I have designed and ordered some machined flanges / starters. They were much more expensive, but they should solve the problem properly and should look good as well.

I made the front tank mounts and got them welded onto the frame. I will still add a gusset and clean them up properly when the frame eventually goes to powder coating.

I also made some temporary seat mounts so I can remove and reposition the tank and seat accurately. With that done, I can now finalise the airbox design ready to make the mould pattern.

I fitted the connectors for the Shindengen rectifier (FH020AA), and taped up some more of the loom.

It will sit just in front of the air filters, so I now need to modify the airbox pattern slightly to give it a bit more clearance and a flat section for it to mount to.

I have almost finished the airbox design and have had some quotes for a carbon fibre version.

Most of the electrical system can now be hidden under the tank.

I have replaced the original battery and starter cables. They had stiffened with age and were slightly too short for the revised battery position. The new cables are much more flexible, and I believe they are around 16 mm², which is similar to some of the upgrade kits people use.

I have also now got the rectifier I am going to use, a Shindengen rectifier (FH020AA), and I am waiting for the connectors to arrive.

That will let me reroute more of the loom and package it more neatly behind the frame. Some of the connectors will also be depinned, re-terminated, or replaced when I tidy the loom up properly.

Once that is done, I can fabricate the front tank mounts.

I have now managed to get the ECU, battery, fuse box, and most of the relays hidden under the tank. Getting the ECU and battery in there has been difficult, but I am hoping it will be worth it if it leads to a cleaner seat and tail section with the exhaust routed underneath.

Once I have tidied the wiring loom a bit more, made the remaining brackets, and finished the final airbox pattern, I will post some more detailed photos. I want to finish the under-tank packaging before I make the tank and seat mounts final.

The overall silhouette is starting to come together now. A few things will still change. The fairing will likely sit lower and tilt back slightly, the tail unit will probably become slimmer, and I may shorten the Termignoni silencers slightly.

I am still working on the intake and trying to get everything hidden under the tank neatly. I have been using the scanned airbox geometry to work out how much room I actually have under the tank. It is going to be tight.

The cavity will house an Antigravity battery, as there is not enough room for the original lead-acid battery.

There is still more to work out:

ECU location

fuse box location

starter solenoid location

airbox drain

seal and fasteners to close up the airbox

everything else that inevitably appears as the design develops

Once I have arrived at a model I am happy with, I plan on making the airbox in fibreglass. Later on I may be able to make one in carbon fibre.

The shape is challenging enough that it will require a split mould. I have never made anything that required a split mould before, but I have plenty of mock-up pieces to practise on.

I remade the intake modelling blocks using 1D bends instead of 1.5D bends. They are a lot easier to route and give me more freedom with the filter position. Even so, I don't think this system is the right solution, so I am now looking at a different approach.

I have had the original airbox 3D scanned so I can design a new airbox around the space available. I still expect to use the same filters and have them positioned just in front of the tank, but feeding into a common plenum.

At this point I am fairly certain I will use the 999 tank. I think it is one of the nicest tanks Ducati ever made, but I am not yet at the point of no return as I have not cut the subframe. The seat will be slightly higher, although I have not measured by how much. I think that may actually help when routing the undertail exhaust.

Right now I am working out exactly where the airbox fouls the tank and how much of the original geometry I can retain. I have a scan of the original geometry, and a skinned version of it cut back to the point where it fouls the tank. From there I can rebuild the top side geometry and make better use of the room under the tank.

I have also started working on a steering damper mount inspired by another S4RS damper mount I have seen. I think the Öhlins damper is from an Aprilia Tuono. I still need to confirm some measurements and clearances.

The filters have arrived (K&N RC-1250). I have been trying to figure out the intake runner routing using the 3D printed modelling blocks. They are 57mmØ - 1.5D bends, and it has been tight trying to package them while keeping both sides symmetrical. So, I am going to print another set with 1.0D bends to give myself a bit more freedom. With the 1.5D bends I have not been able to route the rear throttle body in the position I want.

I can route both throttle bodies another way, but the filters end up sitting higher, closer to fouling the tank, and the layout is not as symmetrical as I would like.

The new end cans arrived today. Termignoni's from a 848 /1098/1198 (96116107B)

At the moment they are just resting on the subframe to help me get an idea of their size. A lot will have to be cut away to get them into position

I will get the intake fabricated first. Then I will get the tank and seat mounted in position and finish up the subframe and exhaust mounting.

I fitted some parts and seals to the 999 fuel pump assembly this morning.

The connector and pinout of the 999 pump assembly are the same as the S4RS. It connected, primed, and started just fine. There was very little fuel in the tank, and I still did not get a low fuel light on the dash, so there is still some investigation to do there.

I have 3D printed some modelling blocks to help me route the intake system, but I still need to make another set that are more rigid, along with some more jigs so I can improve the alignment. I will also need to grind the tabs off the tank to create some clearance for the filters.

With this layout I may still be able to use the Öhlins damper I already have, which is one of the reasons I have been trying to keep the filters lower than they are on the UNICO MOTO bike. I also think the taller arrangement looks a little odd, so keeping everything lower would suit the bike better if I can make it work. I also looked at routing the filters out through the sides of the frame, but it has been quite tight to make that work.

At this stage I am still not sure whether the intake runners will end up being made in stainless steel or carbon fibre.

I have some Termignoni silencers from an 848 / 1098 / 1198 (96116107B) on the way.

The 999 seat arrived today (59510521A), although it will need recovering.

I'm not sure how i feel about the 999 tail unit, it seems a bit bulbous to me. I think I will use it to make a pattern for a fibreglass tail unit instead.

The original airbox fouls the 999 tank pretty badly, so I am looking at intake options. A pod filter setup would hopefully save some space under the tank.

I would still prefer to keep some form of airbox if I can make it work. At the moment I have not found a way of doing that with the 999 tank. Even with the open airbox cover or an MWR filter, I do not think I am going to get anywhere close to retaining the factory airbox in any sensible way.

I also do not think there is enough room to modify the underside of the 999 tank, and I would rather avoid sacrificing the tank to find out unless I absolutely have to. I think the rear of the airbox would end up very close to the top side of the tank, or at least very close to the filler cap area. I have not made any measurements yet, so that may still prove less severe than it looks. Even if I did go down that route, I am not convinced it would leave much more room for the ECU and battery.

I may soon have access to a 3D scanner, so I have also started thinking about designing a completely new airbox, and possibly making it in carbon fibre.

I have also been considering a setup similar to a bike by UNICO MOTO, with pod filters positioned just in front of the fuel tank. One complication is that I had planned to fit a steering damper in that area. I already have an Öhlins damper on the shelf, so I would try to position the filters slightly lower.

There are still a few details to work out, including what to do with the crankcase breather, possibly just using a typical breather filter and venting it to atmosphere. I am also not certain what I would do with the hose from the airbox to the stepper motor.

The area under the tank does not actually look too bad for room once the airbox is removed, so I am going to do my best to package as much as I can under there and keep the rear of the bike clean. For the exhaust, I am thinking about using some Termignoni silencers from an 848 / 1098 / 1198 (96116107B).

I fitted a 999 mudguard today. I have never really liked the look of the original. I had seen another S4RS online with a 999 mudguard and thought it looked much better.

The fork lowers are a little more protected, but the oil cooler and radiator are more exposed. I am not certain yet whether I will stick with it, I need to think it over.

S4RS mudguard (Original)

I have managed to get hold of a 999 seat, though it does not fit as expected. The foam seems much thicker than it should be. I had expected it to sit much more flush with the tank as per some of the 999's / 749's I have seen.

After another look, I am fairly sure the seat itself is the issue rather than the bike. Even off the frame it still does not sit correctly.

The part number on this seat is 55510531A. That is not the same as the part number shown on the Ducati parts website, which is 59510521A.

It is just bare foam and does not look modified, at least not in any obvious way. The only thing I can think is that it may be some sort of factory option for taller riders.

In any case, the seat has been returned and I have another on the way.

I have not committed to cutting the frame yet, I want to get as much as I can working before I go past the point of no return. The original tank is sat on the garage shelf drying out. I am keeping it just in case I have to revert back to it.

My main concerns at the moment are the compatibility of the 999 fuel pump / fuel level thermistor assembly, and what I am going to do with the airbox, as that will probably dictate how feasible the tank swap is.

I have a Ducati 999 tank, so I decided to offer it up to the bike and see how it looked.

It has me considering a Streetfighter build. It is probably more bother than it is worth, but curiosity got the better of me.

I recently bought a Ducati S4RS (2008 - 12k miles) as a winter rebuild project. Although it's running very well, it is clear it has not had an easy life.

From a distance it looks fairly tidy, but the closer I look, the more issues I find. The tank has expanded, the paintwork has picked up plenty of damage over the years, the engine paint is heavily corroded, and the radiator has seen better days.

I have just started stripping it down, so I should soon be able to see what needs attention.