BMW started building single-cylinder motorcycles in 1925. Then the 247 cc lightweight (110 kg) R39 was introduced. Features of the R39 motorcycle were a dry single clutch and a drive shaft with encapsulated bevel gear and hard disk. And because you don't have to change what is good, the single-cylinders were continuously developed between 1925 and 1967, but BMW remained faithful to the design.
A long history
Before BMW presented the R39, the brand had already released the R1923 boxer in 32. A clean, quiet, vibration-free and for its time fast motorcycle, with shaft drive. The problem for BMW was that the single-cylinder R39 was hardly cheaper than the two-cylinder R32 and by the end of 1927 it was no longer worthwhile to continue producing the R39. .
In 1931, BMW introduced the successor to the R39. That became the cheap and practical R2. A pressed steel frame, 95 kilo heavy, 198 cc (and therefore tax-free). Such an 15.000 has been sold in five years.
In 1932 brought the R4. The 12 hp strong engine turned out to have such a smooth character that solid army orders were immediately issued. After the R4 came the R1936 in 3. In 1937 it was time for the R20. This again had a normal tubular frame and the first mono a telescopic fork. It also had a three-speed gearbox and a tool box on the tank.
The end of the sheet steel frames
The R35 was the last mono in 1937 with a pressed sheet steel frame and now also with a telescopic fork. This engine is widely used in the German army. When Germany increased the tax-free displacement of 200 to 250 cc, the R23 arrived. This was the same as the R20 on the displacement and power. In 1941 the construction of one-cylinder was stopped. Because of the war, the 7 would take years before BMW again presented a single-cylinder engine.
BMW a cylinder engines after the war
The R24 was a mix of pre-war types. The engine was more powerful and smoother than its predecessors with the same engine capacity. He had a new alternator with an automatic advance and a shock absorber on the main shaft in the gearbox. His successor, the R25, already came in 1950. A new tubular frame with plunger rear suspension, interchangeable wheels, straight spokes and a slightly different front part made the R25 an even better engine. In 1952 the R25 / 2 appeared, which had been changed in detail.
The R1953 / 25 presented in 3 was a completely new motorcycle and became a bestseller for BMW. For the first time, a mono got a damped telescopic fork, 18 ″ wheels with full hubs and light-alloy wheels, a clutch with diaphragm springs with a power output of 13 hp.
1955 Is the year of birth of the R26 it. He delivered 15 horsepower and had a swing arm in front (Earles front fork) and rear. The cardan shaft now entered through a fork leg.
After the R26 came the R1960 in 27. It was the highest-powered single-person from BMW to 'the modern age'. He delivers 18 hp at 7.400 rpm and had a top of 130 km / h. The most striking thing about the R27 was the rubber suspension of the engine block in the frame. This eliminates many vibrations. 1967 is the last BMW single-cylinder push rod production year.
And the honor of these brave single pitters, which is held high by the members of the BMW Mono club. And those are all really nice people.