This project was born out of a dream, a long standing want for a vintage Speedway solo that could be ridden on the street. Our rider Jake is a Speedway fanatic, and has been most his life. Not a racer, he wanted to enjoy the style of the build in an every day capacity. We had discussed the dream build of this bike 3 years before it started, a few emails and phone conversations ended with me saying “We can make it happen, just go buy a motor, find a pre-unit gearbox and get some details on a speedway frame we can work with.”
After that I thought nothing of it, carried on with building the bikes we had on hand until years later I got the call telling me he was ready to go, and had all the parts. Time to put some metal where my mouth is. The parts we were delivered consisted of a GM500 Upright speedway solo engine, Mikuni VM round slide, and a TTi Norton/AMC 4 speed gearbox. From here it was up to us to create something that echoed era’s of vintage speedway.
Our inspiration came from 20’s and 30’s dirt track racers, speed way bikes, and Jake’s ultimate passion for the sport and it’s history. We approached the build with a completely clean slate, designing from the ground up a bike that would look at home covered in dirt, trackside but held the craftsmanship and qualities of a show bike.
The build started with some sketches, and decisions around wheel sizes to begin building the frame. Using a speedway solo to measure that Jake had bought to sit in his living room.
A typical set up for a speedway solo is an 18”or 19”rear, with a 23”up front. Building off this foundation I began designing a frame with detailing reminiscent of Early dirt track racers with the Art deco styling that came with it. From true racing geometry we’ve borrowed a steep neck angle, but extended the wheel base to create a better line for the tall motor, and creep closer to a street bike set up for stability and rider position. Built from chromoly tubing with the rear section being heavy walled so we could keep the frame visually light, and maintain the rigidity we need.
Mixing hard lines with sweeping curves to accentuate the oversized front wheel. Clean but ornate detailing, hand fabricating what would eventually look like casted frame neck, and axle plates and laying out the geometry around our engine and gearbox. Everything on the frame was designed, and hand built at Purpose Built Moto. With this came a lot of firsts for us, conceiving an idea from scratch with very few boundaries. Putting the time in to craft something timeless and true to my own style. Once the bones of the frame had been finished we templated and planned out the engine and gearbox mounts.
Made from billet aluminium plates and detailed with the obligatory speed holes, the engine, gearbox and rear wheel were now aligned and in place. We’ve used a set of modern racing hubs laced to aluminium rims. The rear runs a cush drive and sprocket/rotor combo with wildwood calliper keeping true to the minimalist aesthetic of a true speedway race bike. The sprocket/rotor combo was designed in house and machined by a friend of the shop to maintain correct gearing. As this bike was to be engineered for street use we’ve fabricated a custom rotor and calliper combo up front custom making a front brake for a springer style front end isn’t an easy thing to make look nice and fit the build. With some trial and error we’ve managed to make a clean, and functional mount for the Brembo brake that looks at home on our 1930’s style set.
To get this build sitting on its own wheels I needed to build my front end. This was a discussion between Jake and myself that lasted a while as we decided on the perfect set up for his bike. Modern speedway fronts are ugly, vintage speedway didn’t look all that fun to make. I conceived an idea of a hybrid springer fork that utilises telescopic forks as the suspension, sketched it up and got an instant tick of approval from our rider. This satisfied both our desire to create something unique and fitting for his one of a kind build, and gave me a huge machining and fabrication challenge.
Anyone can fit a custom front end of swap a set of forks, but fabricating from scratch a functioning springer fork completely of my own design was a goal I had set for myself and wouldn’t stop until I got it. Starting with some lazer cut raw materials, the machine work began. Turning up the headstem, mounting bosses, fork lower mounts, and fork tubes. Using a set of hardened chrome rods for the fork stanchions. All these parts strewn across my fabrication table it was time to get well aquainted with my milling machine. Adding detail to the rear leg, milling the bracing, machining the cross bar for the telescopic forks and machining up the top clamp and bar mount.
The end result is a completely bespoke design, functional, solid and most importantly a beautiful piece adorning the build. Making this part was a stretch of my skills at the time and taught me a lot. The only problem now is I have a bunch of other ideas I want to try out and build. You can watch the whole process of this front end build on our YouTube channel.
The handlebar style was borrowed from early royal enfields, you will notice similarities here with our project delta build, with a reasonably flat profile single mount point and internal throttle and wiring. Although this custom bike is very bare bones some things were absolutely necessary for the bike to be put on the road. Handlebar switches and lighting being the most important.
So what headlights do speedway bikes run? The job here was not to build a speedway headlight, but to create something that you would see on a bike, maybe repurposed from an old car, just as the chopper forefather’s would have done. Re-build, re-use, re-purpose. The solution was a set of B-51 guide lights, rebuilt and chromed out, fitted on a custom bracket that hides the wiring. Something avant garde and a little more flashy than the rest, but I can’t hide who I am completely on these builds.
We were now looking at the skeleton of our build on its own wheels, with ideas flying around about how to dress this beauty with body work. A few more sketches and the sheet metal was pulled out and templates cut. I have a habit of over detailing, or making complex intricate shapes that I really had to pair back on this build. This project was about nostalgia, history and paying homage to a forgotten era of racing.
The design here blends elements of 80’s speedway racers, and early peashooter board track styling. The gas tank housed between frame rails, kept thin and minimal and holding an integrated speedometer opposite the fuel cap. Hand shaped, and finished with polished panels on the side, lightly detailed with some body lines put in with the bead roller. The oil tank and rear fender are much the same, simple, elegant shapes each complimenting the other to become part of the whole. All hand shaped, finished and set in place with custom everything.
I took some time to really think through the detailing on the rear fender struts, usually I will opt for a more ornate and flowing style, here we went for pure function, and industrial style, just as you would expect to see trackside. Steel flat bar, machined out for detail with a grab bar fabricated to house the rear brake light.
The engine on this bike was pulled straight out of a classic speedway bike, usually run on race fuel, and full noise for about 5 minutes at a time revving to around 7000rpm. A 500cc, 4 valve chain drive OHC engine capable of about 70HP I’m told. This one however was dropped to 11:1 compression and modified to run on pump gas with a Mikuni VM carburettor. It came to us built already, but after a few test run we noticed some significant oil leaks and a few things that needed to be addressed. What I will say here is that race track good, and street bike or PBM good are 2 different things. So we spent some time repairing, machining and bringing the engine up to spec with a few modifications for our external oiling system.
The GM speedway engine is designed to run for short bursts, on race fuel that keeps things a lot cooler, with a minimal amount of oil (800ml) that is splash feed to the head via the timing chain, and into the crank via a worm drive. Our approach to keeping the engine cool was first adding cooling fins to the rocker cover then designing an external oiling system.
Our oiling system runs through an external oil filter borrowed from a Harley Davidson Panhead, and through the main downtube on the front of the frame as it pumps it’s way to the feed that was machined into the rocker cover. Run by a Jawa external oil pump common on bikes of the era. This increases the volume of the oil system significantly, as well as exposing it to a longer run of oil lines exposed to air cooling.
The exhaust has been sand bent from 2” 316 stainless steel tube, completed with integrated muffler and a well placed hand made turn out and tip, polished and now perfectly golden after the test rides.
Final touches before paint were the primary drive belt cover, and seat mount. The primary cover is a functional piece that flows from front sprocket to gearbox with a machined clutch pressure plate cover. A mix of machined and hand shaped sheet metal aluminium parts. The seat mount was shaped to match a messinger vintage racing seat, hand made in New York.
For this I wanted to have a bit of give for the rider, but standard style seat springs would ruin the flow we had created with the frame and oil tank. The design here called for a leaf spring style mount, starting on the back bone, and stretching rearward. The result is a beautifully floating seat that flexes with the rider. Made from a set of modified trailer leaf springs, re-shaped, detailed and sent off for chrome.
Time for paint design and again Justin from Pop-Bang classics got the call up. I made a few sketches of the design and we conversed about the right way to pull it off. As usual I wanted the work to do the talking on this bike, rather than a wild paint design. The bone grey was laid as a base with cherry red, white, and black pinstriping detailing the separation between paint and polish. Some subtle inclusions on the neck of the frame with the Purpose Built Moto Delta taking pride of place, and the Signature series badge placed under the oil tank. Let there be no doubt that this build came from our garage, if you couldn’t tell already.
The ride of this machine happens in black and white, strong nostalgic feelings as the single cylinder thumps away beneath you. The odd shift pattern on the right foot lets you know you’re riding something different, unique. With each hand made system working, talking to each other resulting in a one of a kind experience for the rider. From top to bottom this entire machine was conceived and brought to life by the hands at Purpose Built Moto. A lot of motorcycle builders can have careers that span decades and not have the opportunity to build something completely from scratch. For that opportunity I’m truly grateful.
As the skills grow at PBM, so does the ambition to create. This build is again a level up in concept, creativity and finish from the bikes that come before. A huge milestone in our story as we release our first completely in house built motorcycle. As a sign of things to come for us, we are pushing towards creating completely unique motorcycles for collectors and enthusiasts that love and support what we do here. As a builder, I’m consistently grateful for the opportunities presented to Purpose Built Moto that allow us to build our own legacy and be a part of our customers story.
As a personal note to our rider and customer that commissioned this piece, Jake Tobin. Thank you for your confidence, belief and support as we worked to build your dream motorcycle.
Thanks for taking the time, make sure you check out our build run down on YouTube, and the Studio Shoot Gallery here
Tom
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