Motorworld’s newspaper №84
After the end of the First World War, German manufacturers of aeroplanes were on the edge of the abyss – Germany was forbidden to develop aviation. But, as always happens in the years of devastation, the profits of food producers went through the roof. Because of the inflation, it was useless to carry money to the bank so in 1920 Friedrich Kleeman, financial director and co-owner of the prosperous Rex Konservenglas Gesellschaft (The company of canned food in glass banks Rex”) acquired a controlling stake in the engine company Columbus Motorenbau AG. Columbus was making aircraft engines during the First World War. Under the new management company started more prosaic production – producing Gnom engines for bicycles.
First Horex motorcycle, 250 cc OHV engine
Motorcycle Horex made after produced after the merger with Columbus
Sons are often more ambitious then fathers and Fritz Clement, the son of Frederick confirmed the rule. Why the company that makes the aircraft engines, can not produce a full-fledged motorcycle engine? The first Horex motorcycle appeared in 1923, with a 250-cc OHV engine. The name of the motorcycle was formed from two syllables: “Ho” – from the city of Bad Homburg, which housed the factory of the new firm, “Rex” – from the brand of canned food. The sales went so well that in 1925 the two companies merged, although the motorcycles were selling under the brand Horex, and the engines (which were used by other German motorcycle companies) – under the Columbus brand.
It’s interesting that the production of the new conglomerate was marked by a clear English influence: single-cylinder 4-stroke engines with a vertical cylinder arrangement had a chain drive to the gearbox. In the 1920s the company acquired a license for the production of English Sturmey-Archer engines. It was also continued with the talented designer Hermann Reeb which headed the design department in 1929.
But soon Reeb decided to develop a motorcycle with a larger engine capacity. And he chose a completely unusual for that time layout: two parallel cylinders. This layout was not something completely new but was not used for road bikes (racing motorcycles Peugeot used this scheme with great success in the early 20-ies). The designers were embarrassed by the large overall width of this engine, its unbalance, and, most importantly, the poor cooling of closely-fitting cylinders. Only in the second half of the 30s, the parallel twin became popular, with the help of the creator of the legendary Triumph Speed Twin Edward Turner – but Reeb beat him for almost five years (more info in the article about Triumph Tiger “T100”).
The development of the parallel twin engine was started with Hermann Reeb own initiative in 1931. Rebb showed new motorcycle to Fritz Kleeman only by Christmas 1932. The development of the parallel twin engine was started with Hermann Reeb own initiative in 1931. Rebb showed new motorcycle to Fritz Kleeman only by Christmas 1932. It wasn’t the best time for project: the economic crisis and the echo of the Great Depression could not promise good sales for expensive motorcycles. But in the spring of 1933 the market suddenly revived, and Kleeman gave the go-ahead for launching the novelty in mass production.
New Horex entered the market in two versions: a 600 cc 24 hp S6 and an 800 cc 30 hp S8. Both motors had the same stroke – 90 mm, differing in the diameter of the cylinder: 65 mm for the 600 cc version and 75 mm for the 800 cc version. Other parts of the two models were identical. On the light alloy casing, Reeb vertically placed two cast-iron cylinders, with a large gap between them for better cooling. Cylinders and their heads (also of cast iron) were fastened to the crankcase with long studs (four for each cylinder). The crankshaft has a composite structure, with three main bearings, the middle was mounted in a special aluminium plate. Both rod journals were on the same axis. The firing order is offset, so that cylinder 2 fires 360 degrees after cylinder 1, and 360 degrees later cylinder 1 fires again at 720 total degrees, the beginning of another four-stroke cycle.
The drive of the upper camshaft was a chain running in an aluminium casing. For a better cooling, Reeb left a large gap between this casing and the cylinder. A big innovation for that time was a fully enclosed trip valve gear: it was usually opened on OHV engines at that time, collecting dust and oiling the driver’s feet. Hermann used a dry type lubrication system, but at the same time built a 2.25 liter oil tank into the crankcase. Fears that this will cause overheating of the oil, were in vain: tests conducted by the magazine “Das Motorrad”, showed that its temperature didn’t rise above 60º. Also, Reeb used two Amal carburettors.
On the right side of the crankshaft, there were two chains: one drives an upper camshaft, the second one – a magdino and an oil pump. On the left side, the two-row chain transmitted torque from the engine to the four-speed gearbox of the Munich firm Hurth located in a separate block.
Zündapp K 800 from the collection «Motorworld by V.Sheynov»
A new reinforced frame was developed for the leader of the model range. In general, the running gear was typical for those times: the front parallelogram fork, the rigid rear suspension and the drum brakes on the spoke wheels.
Horex S6 cost 1480 Reichsmark, S8 – 1570 Reichsmark. At the same time debuting four-cylinder Zündapp K 800 cost 1550 Reichsmark. As Fritz Kleeman feared: the reason for bad sales was the high price. Production of straight-twin Horex lasted only two years, during this time 82 S6 and 96 S8 were sold. At the same time, Reeb had to deal with the “childhood illnesses” of the engine. On the latest motorcycles, the diameter of the studs that fastened the cylinders to the crankcase was increased from 8 to 10 mm, the lubrication system was improved and the finning was changed for better cooling.
A straight-twin Horex-Columbus engine was used by a small German company Tornax on its model Tornado.
We also should mention a racing version developed on the basis of this engine. Maximum engine capacity for racing motorcycles with sidecar was 1 litre. To get close to the limit, the bore was increased to 80 mm, and the stroke – up to 99 mm, which provided a 995 cc capacity. Cylinders were made of aluminium alloy, heads – made of bronze. But the plate that supports the central main bearing was made of steel instead of aluminium to increase the rigidity. That engine developed 58 hp at 7800 rpm. There were also experiments with a compressor. Racers Brown and Badshin on Horex S8 became champions of Germany in motorcycle races with a sidecar in 1935.
Straight-twin Horex was much ahead of its time and actually became the first serial road bike with a four-stroke twin. Only thanks to a powerful PR of the Triumph most think that the British Speed Twin, which debuted only in 1937 was the first. Hermann Reeb developed a more perfect version of his straight twin already in the 50s – Horex Imperator.
|Manufacturer||Horex-Columbus Werk AG, Bad Homburg, Germany|
|Years of manufacture||1933 – 1935|
|Quantity produced, units||96|
|ENGINE AND TRANSMISSION|
|Engine capacity, cc||796|
|Bore and stroke, mm||75 х 90|
|Engine rating||30 hp at 5000 rpm|
|Carburetor||Amal 6/439, 2 units|
|РFRAME AND WHEELBASE|
|Frame type||Single, tubular, steel|
|Length, mm||2 000*|
|Height, mm||1 100*|
|Wheelbase, mm||1 430*|
|Ground clearance, mm||130*|
|Seat height, mm||700*|
|Gas tank size, l||
|Maximum speed, km/h||