Recently, I got a note from Maarten Janssens, you remember him, he’s the student who designed and built his own 250cc racer from scratch. Some of you commented the work he did on that project was a strong indication we might be hearing more from him and, sure enough, his first racer was just a warm up.
Maarten just turned 22, he’s still studying, but after the first bike was completed he still had an itch to build his dream bike, a bike he could race in a competitive class where prototypes were allowed, so he chose the supermono class.
There’s a lot to see in what he did here, look closely at the rear suspension, and notice the dummy tank and seat buildup, using wire mesh like John Britten. It’s a neat build.
Here’s Maarten in his own words:
The Ducati Supermono was my dream bike, but one thing that bothered me on the Ducati was that the engine was some sort of compromise with the normal v-twin crank using one of the rods as a balancer. Knowing a thing or two about KTM engines I saved up 2000euro (2500 U.S. dollars) working weekends and -sadly- selling parts from the 250RR project.
For that money I got a KTM LC4 Duke 690 engine from 2009 with only a 1000 miles on it + the injection system, wiring loom, exhaust, airbox, throttle system, clutch, radiator and fuel tank. I bought the engine with all these things because I knew I could use them or parts from them. Eventually I used a part of the inlet funnel that was attached to the airbox, I used the fuel pump from the tank, I modified the radiator and used the front pipe piece that fits into the engine. Money well spent I’d say!
Likewise for the Ohlins shock and the Showa race forks from a Ducati 998S by the way! I bought those for $350! The wheels come from the 250RR project but I’m looking for a magnesium rear wheel as I’m writing this.
Designing the frame:The first thing you’ll notice when you look at the frame is probably the rear suspension. The entire point of the bike is mass centralization for accurate and fast control. Although a lot of people are skeptical about it I believe it has a lot of advantages:
1) Mass centralization: because of the position of the spring there is more room in front of the rear wheel than with a conventional system so you can put the fuel there and the spring closer to the engine so an overall gain in mass centralization is achieved. I believe mass centralization on a bike is more important than a low centre of gravity. because the fuel sits underneath the seat the total bike will be more sensitive to rider position.
2) Mass distribution: there is little difference in mass distribution between the front and rear wheel when the tank is full or empty, this makes the bike easier to ride during a race.
3) Room for the airbox: because the fuel could be moved (read above) there is more room for an airbox and electronic parts above the engine.
4) Continuously variable setting of the angle of the swing arm with the push rods: this angle has a great effect on the anti-squat effect and the weight distribution.
5) Forces: the spring forces generated by the swing arm are put onto the spring aligned with the springs axle and working from both ways. they react as negatives against each other! they don’t disturb the frame and aren’t going towards the headstock!
6) Fuel temperature: Because of the position of the fuel it will keep cooler (not closely behind the radiator or above the hot engine) and thus makes it easier to generate more power.
7) Spring adjustments: the spring is easy to reach and (dis)mount and in a couple of minutes I can change the system from progressive to linear and back.
The idea for placing the spring there formed the rest of the bike because of my belief in the advantages above.
The rest of the frame is a basic trellis frame made from 25CrMo4 seamless cold-drawn tubes. The main tubes are 25mm diameter with a wall thickness of 1.5mm. other tubes are 20×1.5mm and 14×0.8mm. More about the frame in the next point.
I had a lot of help designing the pivoting triangles the “push-rod” pushes upon. I now have the option of switching from linear suspension travel to progressive by putting the push-rods in other mounting holes. A local CNC firm made them for free for me from a solidworks file another friend helped me to make. All I did was pay for the blocks of aluminum!
Making the frame(s)
Yes, you’ve read it right! I’m not ashamed to admit I make mistakes but this was a big one! I made a new jig for this frame so I could build around the engine to ensure tight packaging. So far so good.
I started machining all the tubes and started welding them. Now that’s where it all went wrong. I never welded CrMo steel before so I thought it was just the material being a pain in the ass (sorry) during welding and I can’t say that I was content about the result but I carried on. Lucky for me I met the right friend at the right time. I didn’t make all that much parts to fit the frame yet (well I did but I don’t want to think about the old subframe, airbox an air-inlet I had to redo 😉 He told me I used the wrong filler rod. So I chose to make a second frame.
The second frame turned out better because I had a real life example now and I could change little things that made a big difference. I also made it in a manner I thought would be better to avoid distortion due to welding.
I first built the top two “triangles” on a flat plate and connected them with the tubes that run across the frame; again on the machined steel plate. Then I connected this part with other triangles I made to fit the swingarm pivot. Last, but not least, I welded on the headstock, free from any tension of the other welds on the frame!
(Maarten wanted to be sure you knew some of the photos of his build on Facebook are of the old “bad” frame with the incorrect welds so you wouldn’t be too hard on him, but somehow, I don’t think he needed to be concerned about that. – Paul)
Making the swingarm
The swingarm eventually had to be home made so I chose to make an aluminum one that would also work as a part of the fairing. It was made from billet blocks and sheet plate I bent on my working bench. It was an unbelievable amount of work but it paid of! the pictures tell it all.
Since I was on a roll making everything myself again I decided to make the dummy tank/seat assembly myself too. Inspired by the John Britten documentary I bought me some $10 of wire and wallpaper glue and started on making a shape!
I had a lot of help from the guys at Polycress when making the mold. I also received a lot of support from the man behind Tyga-Europe who sponsored me with the fairing + footpegs and exhausts for the project!!
Fuel tank, airbox and subframe
They are made from alloy plate, tube, blood, sweat and yes…tears!
swingarm length (ctc): 600mm
headstock angle: 23.3°
fork offset: 35mm
current weight without fuel: 110kg (242 pounds) (I’m hoping to stay underneath 120kg and I think that that’s reasonable given the heavy wheels.
current horsepower: 72HP (will be tuned!)
current torque: 65Nm
(This project has been very well documented, Maarten took LOTS of photos, so choosing a few to highlight what he did was difficult. Follow the link below to see more of them.)I think it’s important for everyone to see all of the work involved in a project like this, including the mistakes along the way. Look around the Internet and you’ll usually see shiny bikes with perfect paint, ready to ride. They look great and make for a gorgeous photo, but it’s deceptive and all too often, as we’ve seen in many articles, comments begin by critiquing one part or another, how the builder should have done this or that, how the commenter’s Ducati or Honda or whatever is better, cheaper, faster and prettier.
A photo of a finished bike draws the mind away from how it came to be there in the first place. A story like this emphasizes the process, the motivation, the skill, the determination to see it through; making mistakes and learning from them, and then, continuing on.
Many want to say they’ve built a motorcycle, to be able to point to it and look at it, however, the learning and doing isn’t always fun, it can be really hard work, so they never quite get around to it, and then we come across some builders, like Maarten, who know there’s a lot more to having a bike than wishing and dreaming, so he rolls up his sleeves and gets to work. In a few more months, when the Supermono rolls out of the shop and onto the track, if someone asks, he will be able to proudly say, “Yes, I did build that.” Very nice work, Maarten!
Link: MJ Works on Facebook