Vespa PX with engine WR 360 Husqvarna
The amount of work that went into this phenomenal Vespa custom project is obvious! One of our long-term customers, Marek Nachlik, has delivered a milestone in Vespa customising fit for the hall of fame! Here is an account of the production process by the man himself:
"The idea for the project was sparked off by yet another tuned PX motor going arse over tit and blowing up underneath me costing me – once again – a whole barrel full of money. By chance I noticed that the hub on the Honda Comstar wheel possesses a similar mounting hole arrangement to that found on the OE Piaggio items for the PX scooters. With an attitude of 'suck it and see' I bought myself an example of the Honda wheel on E-bay and discovered to my joy and surprise that, with a minimal offset, it is indeed compatible with the Vespa wheel mounting. I drilled out the Honda mounting holes and attached a centralisation device to the hub. This solved the problem of where to mount the rear wheel sprocket and shock absorber. Due to the fact that the drum brake originated from a Honda 750cc motorbike it is definitely suitably powerful enough for the needs of this project.
When I first thought about which motor to use the initial parameter considered was the fact that I wanted something with more than 250cc. This quickly lead to the WR 360 motor from Husqvarna coming into consideration as it is relatively easy to get hold of and the spare parts are easily available and affordable. One minor set-back of the Husky motor is that has its output sprocket located on the right hand side, the Honda wheel sprocket however is on the left. Luckily the simplex drum brake assembly can be simply turned over, leaving the sprocket on the correct side.
The next part of the process involved fabricating a swing-arm, preferably made of steel for easier modification. At this stage I still hadn't really begun to take the whole thing seriously or even hope that I would ever have it anywhere near complete. In the end I decided upon a swing-arm from a Yamaha XS 400 to modify for my purposes. The bracket to hold the motor in place was then also fabricated from steel plate. To check the overall proportions I mounted this part of the assembly into a Vespa frame, from which I had already removed the rear half. The main plan had evolved to having a centrally positioned motor with a completely removable rear frame unit, including the sidepanels. These factors determined the final situation of the Husky motor and also the final maximum length of the swing-arm. I shortened it to a suitable length and welded it to the motors holding bracket. I had decided to construct the rear shock absorber mechanism underneath the scooter, similar to the assembly found on Buell motorcycles. This solution was necessary due to the removable rear frame being no longer suitable to incorporate a shock absorber mounting. The suspension leverage system was designed to create identical strength and travel at each end of the mechanism. The lever was then attached to the bottom of the frames tunnel which I also reinforced through to the legshields using 2.5mm thick angled steel plate. The swing-arm fixing bolt with a modified thread from the Vespa Cosa was used here and to further strengthen the tunnel section I added a steel cover, which also helped to hide the existing reinforcements.
For a better fit underneath the rear frame I had positioned the Husky motor tilted 45° towards the front of the scooter. As a result its kick-starter shafts stub is located underneath the top of the sidepanel, making its operation anything else but practical. The solution was to extend the kick-starter shaft and support it, while attaching a suitably dimensioned sprocket to the end. The sprocket would then be turned using a chain, allowing the kick-starter itself to be mounted in a more user-friendly position. I took a kick-starter shaft from a Vespa PX motor, machined away the now unnecessary features and adapted it to accept another sprocket to operate the lower end of the connecting chain. To my delight the whole construction worked from the word go and did not require any further modification. I now turned my efforts towards assembling the removable rear frame and also its correct positioning. This involved sawing yet another donor frame apart as the new frame needed extending by 10cm, 4cm to the front and 6cm to the rear. To hide this elongation successfully the sidepanels from a Vespa Sprint model proved ideal, due to fact that they are noticeably longer than the sidepanels found on other Vespa models. Their inclusion also made the 'Fake-Oldie' look inevitable. I was then offered an Indian Bajaj frame which I rapidly purchased in order to promptly saw it apart to supply all the parts required to complete the final look of the frame. The horncover is a separately obtained repair/replacement item and the steering headset, from a Vespa Rally, was found at a scooter-parts fair.
Due to the space underneath the rear frame being extremely limited there was no room left for a fuel tank. The area beneath the frame was occupied by the shock absorber assembly so I decided that the legshield toolbox would have to do. We started with a new toolbox, matched and modified the dimensions and finally coated its inner surface with a fuel tank sealant. The fuel delivery is now taken care of by a 'Hardi' fuel pump. Following closer inspection it turned out that the Husky motor was in a much worse mechanical state than originally hoped. The piston, cylinder, con-rod bearing and the water pump were all knackered, leading to a complete overhaul and the piston being replated by the experts at 'Powerseal' in the Netherlands.
Now that both the rear and front half of the frame, including the toolbox fuel-tank, were in shape it was time for the first complete assembly of the whole scooter. A water-cooling radiator was attached to the front using a luggage rack and cable-ties, fuel put in the tank and the motor was fired up for the first time following its rebuild. The initial smiles were quickly replaced by the decision to start work on the exhaust! My lack of expertise in this field led to the job of fabricating a custom expansion-pipe being outsourced to a competent specialist in the form of Markus Rentzmann from 'Pipe Design' in the neighbouring town of Bremen. He delivered the goods in a brilliant style and we were all impressed with his efforts. While the scooter was at the exhaust workshop in Bremen I used the time to get started sorting out the steering column and front suspension. The fork assembly found on the Vespa Cosa model has adequate damping qualities and also provides a suitably dimensioned brake unit but I find that they are a little too bulky in appearance for this project and decided to remain with an old-school trailing link version. Another reason was in order to better match the look of the rear wheel assembly I had the idea to build a wheel resembling the 'Centerline' wheels found on many drag-racers. The disc brake is a further development of the front brake I constructed for my previous custom Vespa 'Stray Bullet' and its spoked front wheel. This had the obvious advantage that the second time around it was easier to put together and the whole fork, front wheel and brake segment was dealt with in just two months.
Having the scooter back from 'Pipedesign' in Bremen, complete with exhaust, meant that I could finally weld the left-hand sidepanel in place, mount the steering column assembly and arrange the final position of the front mudguard. To finish off the frame modifications the radiator holding bracket was welded in place, now the steering assembly could be considered. The headset was chopped, dropped and prepared for the electronic 'Motoscope Pro' speedometer unit from 'Motogadget'. The seat also had to be custom built as the extended length of the rear frame meant that the items available for standard Vespa frames are all exactly 10cm too short. Its design had to be completely integrated into the general form of the rear frame but I also required it to be hinged. To allow the seats hinge to be completely hidden I constructed a virtual, or remote, seat hinge folding mechanism and added a locking device, taken from the bonnet latch of an old VW beetle. As with the VW beetles filler-cap cover this item is operated remotely by cable and is actuated in this case by pulling the other end of the cable which I situated underneath the Sprints left sidepanel hatch.
The wiring loom and electrical components are all from 'Motogadget', while the indicators and switches are from 'M-Unit' and 'Motoscope' respectively.
I deliberately chose the simplicity and ease of repair of a fake classic-look paint job to counter the inevitable problems that could be encountered during the otherwise complicated construction process. The removable rear frame arrangement can also quickly lead to unintentional scratches or other minor damage occurring while in use.
The first test-ride exposed the difficulty encountered while attempting to change gear. My initial idea was to simply take the ratchet block from the PX models gear-change mechanism and weld it to a modified gear-change lever. In theory it seemed good enough. Practice showed that there was a problem concerning the force needed to operate it versus the practical distance required to select the gears correctly. I ruled out any possible further purely mechanical solutions and chose instead to install an electro-mechanical gear changing cylinder produced by 'Klicktronic'. These clever little devices are generally found on go-kart motors or motorcycle conversions for riders with artificial legs. The catch with this technology is that with a peak-power requirement of around 35A the Husqvarna motor, which has an electrical output similar to the inadequate values produced by Vespa motors, needed an electrical upgrade. I re-soldered the stator and added an ACϟDC voltage regulator. The H4 headlamp was replaced by a LED item produced by 'Adjure'. The motor now produces a stable 13.8V of current when running.
Following even more testing we gradually solved the rest of the small, niggly problems successfully but, as always with a project like this, its not over yet! For example: The vibration caused by this set-up requires a modified set of motor buffers to be made at some point in the future.
The performance this scooter delivers can only be described as monstrous! 55 hp and 45 Nm combined with a dry weight of only 145 Kg means this baby can rocket you into orbit and beyond!