Gnome et Rhone is a French company that was famous for manufacturing aircraft engines of an unusual design — the crankshaft was rigidly fixed and the rest was rolling around it! Despite the inherent imperfections (in particular, it was extremely difficult to regulate the speed of engine rotation, which is why those engines would support the ‘all or nothing’ principle), the Gnome et Rhone was the most popular brand at the beginning of the WWI: 25,000 engines were produced in France, 75,000 were manufactured under the licence in Great Britain, Russia and… Germany.
In the aftermath of the war, with a sudden drop in demand for the aircraft engines, the company’s management couldn’t decide what direction it should take. Eventually, they have followed the BMW’s footsteps and started a motorcycle production. But since the engineers from Gnome et Rhone didn’t have such experience, they’ve decided to buy a license from the professionals. The very first model that they wanted to make was the ABC motorcycle, designed by Granville Bradshaw. It was the first motorcycle in the world equipped with a boxer engine with the cylinders fitted across the frame. The Bradshaw’s bike didn’t have the rear wheel drive fixed to the shaft [Max Fritz, the core engineer from BMW, would come up with this idea a few years later]. But unlike the first BMW models both of the wheels of the ABC motorcycle had a soft suspension.
From 1920 to 1924 the company produced around 3,000 of these unusual and quite expensive bikes and then switched to more “trivial” models. But their love for boxer engines hasn’t gone anywhere, and in 1930, they’ve presented the new generation of motorcycles with 500 cc 2-cylinder boxer engine. Their main features were: the rear wheel drive fixed to the shaft, stamped duplex frame and the front parallelogram fork with powerful stamped arms.
The Gnome-Rhone 750X, presented on the Paris Salon in October 1935, became the crown jewel of the whole lineup. It had a 724 cc 2-cylinder overhead boxer engine that produced 34 hp at 5,500 rpm. It was one of the fastest and most powerful motorcycles in the world at the time. It could achieve the speed of up to 150 km/h in solo version and 110 km/h — in combination with the light Bernardet Sport sidecar. Of course, the British Brough-Superior demonstrated a better performance, but at a much greater cost.
The Gnome-Rhone engines and BMW motorcycles fitted together perfectly. Connecting rods with sectional lower heads were positioned on a crankshaft on the roller bearings. One of the camshafts was located over the crankshaft, and the original feature of the bike was the additional pusher between cams and rods. The massive oil pan was attached to the bottom of the crankcase. The rear wheel was driven by the dry single-plate clutch, 4-speed gearbox, and shaft.
The Gnome-Rhone had a typical duplex frame [made of molded elements] that had something in common with the German analogs. This machine could be equipped with a sidecar because of its structural strength. It had a parallelogram front fork with stamped arms and friction shock-absorber and a rigid rear suspension. It’s interesting that in those days the company already understood the benefits of customizing: for example, one could order a chrome tank or lamp housing.
In its motorcycle commercials the Gnome et Rhone company has always placed emphasis on the “aircraft quality” of its products. In order to confirm this claim, it promoted and participated in the all kinds of driving randes and record runs. Thus, on September 5th, 1936, the famous racer Bernar got behind the wheel of the Gnome-Rhone 750X (with a sidecar!) and surpassed the Orient Express on the Budapest-Paris route, it covered 1,519 km in 23 h and 28 min. No less impressive were the other two record runs on Linas-Montlhéry Race Track in 1937-1939. Among the most remarkable records during those sessions were: the 24-hour run with an average speed of 136,563 km/h and 50 000 km with an average speed of 109,380 km/h. In total, the Gnome-Rhone 750X holds over 108 world records, some of them are undefeated till this day.
The army version of Gnome-Rhone — model 750XA — was developed at the same time as civilian X model. Under the contract, the company had to produce 405 copies of this motorcycle [Bernardet DP sidecar versions] until March 1st, 1936. The main difference was that the engine of this model contained one carburetor Solex instead of two AMAC — it was a big plus because now there was no need for synchronization. Gnome-Rhone 750XA had an original system of carburetor heating: from exhaust port some of the gas traveled to the carb through a special pipe. In this version the engine had a reduced power of 28 hp, but still it remained above average rates that most of the military bikes had at the time.
The chassis of Gnome-Rhone 750XA has been enhanced, the road clearance raised up to 180 mm. Instead of 3,50-19 tires, the 4,00-19 tires have been installed. All three wheels, including the sidecar wheel, became interchangeable.
The army version of the bike showed its reliability during the marathon. All military engineers were absolutely amazed by the new generation of Belgium motorcycles with a sidecar wheel drive. This technology has been licensed on February 3, 1937. In the same year the company produced 15 copies of Gnome-Rhone 750XA RM for testing, but this model didn’t go into serial production.
The production of a new army motorcycle Gnome-Rhone AX2 with 800 cc flathead engine with a capacity of 18,5 hp had started in 1938. The “old” overhead 750 cc engine was last used in 1942, when Vichy government has ordered 50 units for the security escort of the highest officials of the State. These motorcycles, known as Gnome-Rhone X40, were used until 1952 by the escort of Henri Pétain, Charles De Gaulle and Vincent Auriol.
|Manufacturer||Société des Moteurs Gnome et Rhône, Paris, France|
|Years of manufacture||1935-1940|
|Quantity produced, units||N/A|
|ENGINE AND TRANSMISSION|
|Type||2-cylinder, 4-stroke, boxer|
|Engine capacity, cc||724|
|Bore and stroke, mm||80 х 72|
|Engine rating||28 л.с. при 4200 об/мин.|
|FRAME AND WHEELBASE|
|Frame type||Stamped steel duplex|
|Wheel size||4,00-19, грязевой протектор|
|Ground clearance, mm|
|Seat height, mm|
|Mass, kg||180 (solo), 320 (with a sidecar)|
|Gas tank size, L||20|
|Maximum speed, km/h||78|