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BMW R 75/5 in comparison with the R 1200 R Classic

Yesterday and today

BMW has been building air-cooled two-cylinder boxer motorcycles since 1923. An R 75/5, whose series heralded a more modern boxer era in 1969, looks technically very old next to a current R 1200 R.?

The history of the BMW motorcycle begins in 1923. Then BMW chief designer Max Friz blocked an air-cooled two-cylinder boxer engine with a displacement of 494 cm 3 and 8.5 hp with a three-speed gearbox, developed a few years earlier by Martin Stolle, and transferred the power directly to the unsprung rear wheel via a clean cardan drive. This engine had been driving the Victoria KR1 since 1920, but with cylinders arranged lengthways and an open-running flat V-belt to the rear wheel. The BMW named R 32 was a great success. It remained on the market from 1923 to 1926: it weighed 120 kilograms, reached a top speed of 95 km / h and was timelessly elegant.

No, we’re not writing BMW history, we just want to compare the BMW R 75/5 from 1969 with the popular R 1200 R. Yesterday: The two-valve carburetor engine of the R 75/5 made 50 hp at 6200 tours . The 745 cm³ engine marked a more modern type of two-valve boxer due to its design. The unmistakable BMW engine made it into the R 100 models with 980 cm³ and up to 70 hp. On his journey through almost three decades of construction, he fired the R 80 GS Basic, which was built until December 1996, to say goodbye. Over the past 27 years, well over 250,000 such two-valve boxers have rolled off the production line in Berlin.

HToday: The 1170 cc four-valve engine of the R 1200 R starts up with a quick push of a button and immediately runs smoothly. He bubbles discreetly, prottelt like always. Logically, BMW has remained true to itself with this drive for almost 90 years: transversely and therefore with the hot exhaust sides well positioned cylinders (now plus oil cooler), even firing order, cardan.

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Brands, Myths and Engines

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Forms of yesteryear: bellows, toaster tank, elongated lamp bell, fat two-man bench, sheet metal fenders.

Still, the boxer drove wobbly with the short swing arm near top speed. The straight-line stability only improved when the swing arm and with it the wheelbase grew 50 millimeters in length in 1971. Like this 1973 copy. The elevator effect remained noticeable, once rubber cow always rubber cow, that’s that. The suspension comfort of the chassis remains positive, even by today’s standards. The way it puts away potholes and manhole covers is simply sensational.

The standard, narrow, ideally cranked handlebar is easy to reach. The soft, boldly padded bench contributes a lot to the high level of seating comfort. Even as a "long swing arm", the R 75/5 catches the most jagged hooks and is very handy for a 750 cc. It has been proven that Bridgestone’s famous BT 45s make the R 75/5 quite accurate and even sufficiently stable.

Despite the happy ticking of the valves: This engine quickly beguiled the sworn white and blue fanatic troop with its more or less true “nothing goes wrong! ”Stories. For a long time there was a kick starter as standard in addition to the electric starter; From the end of the 1970s, it became an accessory that had to be paid for.

Today: Thanks to the double-jointed single-sided swing arm (Paralever), nothing lifts in the chassis of the R 1200 R. Nothing wobbles any more, the R 1200 R pulls its course undeterred, it bounces great, is comfortable and has a secure track. A top chassis in the best BMW tradition. In addition, the R brakes very well, its ABS-equipped stoppers are no comparison to the blunt drums of the ancestor.

The R 1200 R hangs fine on the gas, the boxer accelerates vehemently, is really powerful. But the BMW is more socially responsible than almost any other motorcycle. And in traditional black with spoked wheels, the roadster continues to look like a classic BMW, the big sister of the R 75/5, so to speak. Except for a few designer corners, in which BMW head of design David Robb has let off steam.

Tomorrow: In 2030, we will remember the R 75/5 with nostalgia and melancholy. “50 HP was always enough!” Shout the yesterday from the windows of the old people’s homes, as Hans-Gunther von der Marwitz always claimed during his lifetime. A R 1200 R will be a sought-after young timer in 2030. “110 HP is enough!” We will shout and let our rickety bones fall into the deep seat, press the button with a trembling thumb, engage first gear and enjoy every meter, no matter where.

technology

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The dohc four-valve cylinders are thicker on the outside. Colorful, shimmering manifolds as always, oil cooler.

BMW R 75/5 engine
For the first time in the BMW boxer concept, the cylinders were made of cast aluminum, and the longitudinal crankshaft of the R 75/5 had plain bearings; the boxers previously had cast iron cylinders and crankshafts with roller bearings. From the camshaft below the crankshaft, four very long bumpers led to the right and left cylinder heads, where they operated a valve for the inlet and outlet of both cylinders via rocker arms. The valve clearance was regulated via adjusting screws. The R 75/5 had modern Bing constant pressure carburettors; the smaller / 5 models R 60 and R 50 still had slide carburetors. The single-disc dry clutch was operated mechanically using a cable. In the pivot point of the cardan shaft there was a universal joint, the needle bearings of which often broke. Inspections were required every 5000 kilometers, but valves and carburettors (or their Bowden cables) had to be readjusted after 2500 km at the latest.

BMW R 1200 engine
The four-valve boxer appeared in the R 1100 RS in 1993: with 1085 cm3, 90 hp at 7250 tours, petrol injection and G-Kat. In addition with five gears, cardan in a double-joint single-sided swing arm to the rear axle drive and Telelever front wheel suspension. For BMW it meant a revolution. The current R models carry the last evolutionary stage of the air / oil-cooled boxer engine – with 1170 cm3, two overhead camshafts and four valves per cylinder. It develops 110 hp at 7750 tours, the transmission now has six gears. The 10.1 centimeter thick pistons pile up a full 119 Newton meters on their 73 millimeter stroke. The compression is high: twelve to one (R 75/5: nine to one). A special feature are the four camshafts lying lengthways to the direction of travel: each one controls an inlet and an outlet valve using short rocker arms. An intermediate shaft under the crankshaft drives the four overhead camshafts via timing chains. As before, a single-plate dry clutch provides the frictional connection, which is now hydraulically operated.

Technical specifications

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The rounded valve covers with the cooling fins tapering from the inside to the outside have already achieved cult status.

BMW R 75 / 5BMW R 1200 R ClassicType of engineAir-cooled two-cylinder four-stroke boxer engineAir / oil-cooled two-cylinder four-stroke boxer motorMixture preparationComputer pressure carburettor, Ø 32 mmInjection, Ø 50 mmClutchSingle-disc dry clutchSingle-disc dry clutch82.0 x gearboxFour-gear x.6.0 mmCapacity746 cm31170 cm3Compression9.0: 112.0: 1Power37.0 kW (50 PS) at 6200 / min81.0 kW (110 PS) at 7750 / minTorque60 Nm at 5000 / min119 Nm at 6000 / minWeight fully fueled210 kg237 kgMaximum speed175 km / h220 km / h Price 5845 marks (1973) from 12 540 euros

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