Grand Prix, the Cafe Racer Sportster
Grand Prix, the Cafe Racer Sportster by Ardent Motorcycles
We are so pleased to introduce Curtis from Ardent Motorcycles and his new creation: Grand Prix, the cafe racer sportster…
A little background about me by way of introduction. I came to motorcycles quite late in life. I am an artist by training. I have been a painter and fine art photographer since I graduated from college with my Bachelor of Fine Arts degree.
I started riding just six years ago but quickly got the bug in the worst way. I have always loved building things and it was just a matter of time before I began building bikes, but I had absolutely no mechanical background at all when I began. I had never even changed the oil on my bike when I started customizing my first bike.
After customizing a few bikes, doing paint, a little bit of fabricating, and installing various components, I came to the point where I felt I needed to know more.
I ended up studying motorcycle mechanics and fabrication at a local community college that has an excellent program. I wound up becoming a certified mechanic. While I was in school, I started building bikes from scratch. This bike is my third scratch build and I call it the Grand Prix for the bikes that inspired it.
This motorcycle is based on the idea of creating a classic looking Cafe Racer bike with modern fuel injected engine and sport bike suspension.
The tanks were inspired by the small displacement race bikes of the fifties and sixties, with their tall, boxy sections.
The frame is based on the classic featherbed frame from the Norton Manx. It’s a double hoop style of frame with a nice flat top line.
I chose a Harley-Davidson Sportster engine because I like the torque, sound, and character of the engine. The rear tank on the bike houses the oil, with copper oil lines running down the back of the electrical box, which is under the seat of the bike.
I wanted to do as much hand fabricated aluminum work on this bike as I could, so I made not only the gas and oil tanks, but also a set of partial fairings for the bike and a little headlight fairing as well. I fabricated the frame from scratch and I also built the swingarm, exhaust, rearsets, and a variety of small details around the bike.
Almost every aspect of this build was fairly challenging. Building the frame from scratch and incorporating the Sportster engine mounts was difficult. There is a lot of bending and coping of tubes to do and lots of welding and finishing of welds to get the smooth finish I wanted.
I even made the head tube with the bearing lands in order to fit the front end I acquired. Building the swingarm also required some very precise fabrication and welding. It’s entirely welded up out of flat stock with the ends hand machined from aluminum blocks.
I had to have a custom made sprocket fabricated in order to deal with the large offset created by the wide rear tire. In fact, the rear wheel is turned around backwards to get the drive on the right side of the bike. The brake had to be underslung on the left side because of this.
The tanks and fairings on the bike are probably the most challenging part of the build. All of the panels are hand formed from sheet aluminum using a mallet and shot bag for initial shaping and an English wheel for final shaping. The gas tank is comprised of about ten different pieces, all tig welded and hand finished.
The fairing was inspired by the 60s race bikes. It comes off in about five minutes with Dzus fasteners for access to the engine. There’s stainless mesh up front and it’s open bottom and top for cooling. I’ve had no issues with cooling thus far.
Getting the panels rough shaped and welded together doesn’t take me too long, but smoothing the surfaces takes real time and attention. I hit the surfaces with a sanding block to reveal the low spots, then tap these out with a mallet from behind. The entire surface has been sanded from 80 grit all the way to 1000 grit or more before polishing. A lot of work, but very satisfying and it’s the signature feature of the bike.
I did the painting on the bike as well, using automotive urethane paints and an epoxy sealer to prevent any possible rust. The paint is a metallic gray with a silver metal flake added to the clear for some extra sparkle. The seat and handgrip covers were made for me by a local seat builder. I built the seat pan and he did the foam and leather work.
The components for the bike were mostly purchased on Ebay. The front end is from a GSXR600. It was rebuilt with new seals and bushings before installation.The wheels and tires are for a CBR1000RR.
They worked with the front end with a little bit of adaptation.
The engine was a low mileage engine from a salvage company. I tore it down and surfaced the valves and valve seats. I honed the cylinders and reassembled with new seals and rings.
I had it dyno tuned to optimize it for the pipe and air cleaner. It makes just under 80 ftlb of torque and 80 horsepower.
The pipe was initially left open, but the sound was too harsh and obnoxious, so I put in a couple of adjustable baffles in the muffler to tame it a bit. It sounds great on full throttle.
Wiring was accomplished by modifying a stock Sportster Harness to run through the custom frame and body work. There was a bit of custom wiring to be done to mate the GSXR switches to the Sportster harness. I removed the Harley-Davidson turn signal module because it’s very bulky and won’t handle LED lighting.
I used an Illuminator Pro to power all of the led lighting for turn signals and brake lights. The front turn signals are wrapped around the front forks and the rear run/brake/turn lights are tucked under the tail of the bike.
The battery is a Shorai Lithium unit I chose both for its compact size and light weight. It’s all gets fairly complicated, but if you can read a wiring diagram, you can make it work.
Building this unique cafe racer sportster took almost six months of nearly full time work to complete.
It seems like it should go faster, but all of the little details add up and putting it all together and making it work takes time. There is also a significant period spent on testing and refining the bike once it’s together.
I build just one or two bikes a year because of all of the scratch built components.
I work as an artist would, building what inspires me and then selling it afterward.
If a buyer wants to change components to suit their needs, that’s fine with me, but I like to work from my own concepts rather than a customer’s requirements.
For now, I’m enjoying working with the Sportster engine. I may experiment with other engines in time, but the engineering in making everything work with a different engine is substantial and I want to take advantage of the work I’ve done with the Sportster engine.
The Grand Prix bike is for sale right now.