The story began a few months ago when a group of Solex riders, nicknamed "Team 0", contacted L'Atelier to prepare a "racing" Solex.
This Solex needed to be ready to race on July 8th, for the "4 Hours Solex", a race held annually in the commune of St-Etienne-des Oullières in Beaujolais.
As you may have gathered, L'Atelier is more focused on "original" restorations, and preparing "racing beasts" is not its primary DNA.
However, several factors led to this project being integrated into L'Atelier's schedule:
the enthusiasm of this group of Solex riders was very infectious and we quickly hit it off,
the goals sought were similar to those of L'Atelier: to build a reliable machine capable of withstanding sustained use,
competition also offers the opportunity to effectively test parts and preparation systems "the hard way".
L'Atelier took up the challenge, and a Solex will therefore be entered in this competition in the "improved original" class.
As a base: nothing… only a good condition Motobécane 3800 frame was provided by Team 0.
It was therefore necessary to create an engine and refine the cycle part a little for this endurance race.
The cycle part
This was the easiest operation.
The work consisted of:
checking the rims (spokes, inner tubes, tires) to avoid any punctures or breakages at this level and thus save time in the pit,
changing all the brakes, which were severely tested because the 2.5 km circuit included a fairly long descent ending in a hairpin bend,
lightening the frame of all unnecessary or protruding parts to save weight and ensure better rider safety,
changing the entire "cycle" system: chain and freewheel because pedaling helps support the engine,
reinforcing the bottom bracket axle, which tends to desolder on the frames of the latest Motobécanes.
We will see elsewhere that these last two points are also useful in case of breakdown to return to the pit!
Engine side
At this level, everything had to be done.
So we started with a collection of disparate but excellent condition parts:
roller and ignition flanges, original crankshaft... and that's it!
The engine was mounted on a solid aluminum crankcase.
The crankshaft was reground and polished to adapt perfectly to this crankcase, these two operations allowing a perfect flow of fluids. For its part, the connecting rod received 2 new needle bearings, just to have peace of mind.
From there, a set of new parts were adjusted: roller, ignition coil, 41 3-port cylinder, 11 pipe, high compression cylinder head (without valve to avoid any leakage at this level), new fuel pump, "race" lifting lever, installation of a circuit breaker (mandatory in race) etc…
The carburetor was reamed, equipped with a flat slide and a variable jet by a Solex racing specialist. This person also took care of balancing the flywheel, an essential operation when you start to push the RPMs!
After a few hours of work, we get this:
Solex delivered, the initial tests are conclusive and Team 0 makes some adjustments: removal of the headlight for better engine ventilation, notch in the air filter cover to draw in even more air, adjustment of the variable jet to the circuit to achieve the best compromise and, above all, a spark plug of the correct color to avoid any risk of seizure.
The Race
July 8th, it's the big day.
Between original, improved original, prototypes and super prototypes, there's a lot to see. Some machines are astonishing, but all are different. You go from a completely makeshift Solex, almost reinforced with joint compound and wire, to a fully functional and magnificently machined super prototype.
You also go from an original Solex moving at 35 km/h to a prepared monster reaching 110/120 km/h! And all this on the same track!!
The morning is reserved for adjustments and qualifications. After about ten laps, the Solex is ready and achieves a very respectable ranking: first behind all the super prototypes and even ahead of some "simpler" prototypes. Well done!
2:00 PM: After the final instructions from the race commissioner, the participants set off "Le Mans" style, their Solexes arranged in order of qualification times.
And the race unfolds, minute after minute, hour after hour, punctuated by pit stops to change riders or refuel.
The Solex is running well and manages to do laps in 2.30 minutes. This power and regularity allow Team 0 to occupy the first "inter-category" place and gain many laps ahead.
The afternoon progresses and the heat becomes stronger; one can feel, on all air-cooled machines, that the power is decreasing.
To spare the machine, Team 0 slows the pace a little with passages at 2.50 minutes, thus maintaining a comfortable lead during the first 3 hours of the race.
Then comes the last hour, the Solex continues to run like clockwork for the first twenty minutes then…..it stops!
It returns to the pit "by pedal".
A quick check (too quick?) reveals a... lack of fuel in the tank!
Indeed, the ambient heat, combined with that of the engine, creates a vapor-lock phenomenon within the tank. In fact, as soon as the fuel level is insufficient, the gases "block" the intake.
Once refuelled, it restarts immediately but lacks power.
After another lap, another pit stop allows me to diagnose... a broken flywheel!
This venerable original part, although perfectly balanced, did not withstand the stress of the race and the power of the new engine.
In short, quick disassembly and reassembly of another flywheel and Team 0 resumes the race but a lot of time was lost, alas.
6:00 PM: end of the race and announcement of the results, the team finishes second in the inter-category classification.
For L'Atelier, this experience ends with a rather positive outcome, which above all validates the quality of the parts used and the assembly performed. We will also know, for the next time (?), to reinforce this cursed flywheel or... replace it with another assembly... to be seen!
The experience gained serves us fully!
Thanks again to Team 0 for the trust they placed in us and thank you also for the magnificent welcome you gave us at your stand during this race!
So... L'Atelier might enter a prototype next year... we're very tempted!!
🙂
Don't hesitate to take a look at the slideshow: