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For the 1970 model year, BMW launched three new models having engine capacities of 500 cc (R50/5), 600 cc (R60/5), and 750 cc (R75/5). The R75/5 could reach 110 mph (177 km/h). The "slash-5" series came out just in time to meet the rising demand for sport bikes. All so-called "/5" models were manufactured at BMW's factory in the Spandau suburb of Berlin, BMW having transferred all motorcycle production there from Munich in the late 1960s. BMW had stopped production in Munich of the last “Slash-2” models, with their Earles forks, kick starters, 6 volt electrical systems, antiquated brakes, and frames descended from pre-war BMWs for use with sidecars.
The new, “/5” series of BMWs offered a 12 volt electrical system, electric starters as well as the retained kick starter, telescopic forks, and improved brakes. The sidecar was no longer factored into the design, allowing for better handling. BMW also introduced with this model non-metallic fenders and tail light housings for the first time. The use of plastic and other non-metallic materials resulted in a motorcycle weighing only 463 lb (210 kg).
Model year 1972 saw the introduction of the 15 L (3.3 imp gal; 4.0 US gal) “toaster” tank with chrome side panels, so named because of its resemblance to a kitchen toaster. For the second half of the 1973 model year, BMW lengthened the rear swingarm 2.5 inch (6.4 cm), resulting in that is known now as the “long-wheelbase” 1973½ “LWB” models. This improved handling and enabled a larger battery to be installed behind the engine while retaining the kick starter. In some instances, the driveshaft cover was cut and a splice of the same diameter was welded in to lengthen the cover, as to not waste shorter drive shaft covers in inventory.
The /5 series was the first series to be manufactured completely in Berlin, as by 1969 all of Munich's production capacity was needed for automobiles. "Berlin with its well-trained workforce was an obvious choice. So in 1969 the Berlin Plant started production of the all-new BMW /5 Series, a completely new design and construction following a modular principle all the way from the suspension to the flat-twin power unit."
"With the motorcycle — which, in the 1960s, had been almost forced out of the market by the automobile — starting to re-gain popularity in the early 1970s, production figures at BMW Plant Berlin began to increase rapidly. In 1970 no less than 12,287 units came off the production line and by July 1973, when the /5 model series reached the end production, a significant volume of 68,956 motorcycles had left the Berlin Plant, production increasing five-fold within just three years. Another highlight celebrated at the time was the completion of the 500,000th BMW motorcycle in the history of the Company."
In 1974, BMW introduced the “/6” models, which offered numerous improvements, most notably disk front brakes, more and better instrumentation, and a five-speed transmission. The “toaster” tank, however, was dropped. The front single disk brake was a hybrid cable/hydraulic system. The master cylinder underneath the fuel tank was actuated by a cable from the handlebar lever.
The /5 models are air-cooled, four-stroke, opposed-twin (boxer) engines with hemispherical combustion chambers. The engine is built around a one-piece tunnel crank-case. The camshaft is driven by a duplex chain and is located below the crankshaft (unlike the /2 series which had the gear-driven camshaft above the crank). This reversed arrangement improves ground clearance for the same center of gravity and assists lubrication of the camshaft. Valves are actuated by the camshaft through hardened followers, push rods, and rocker arms.
The 500 cc and 600 cc models are equipped with Bing slide-type carburetors with 26 mm throats. The R75/5 comes with 32 mm Bing CV (Constant Vacuum/constant depression) type carburetors. As in all BMW motorcycles at the time, the clutch is a single-disk dry clutch.
Final drive is by shaft, running from the transmission by universal joint to an oil bath within the right rear swing arm and connecting to a bevel gear and ring gear on the other end. Unlike the /2 models (with the exception of the 1969 R69US), the /5 models are equipped with telescopic front forks, 12-volt alternator and electrics, and standard tachometer and turn signals.
|R 50/5||R 60/5||R 75/5|
|Bore||67 mm (2.6 in)||73.5 mm (2.89 in)||82 mm (3.2 in)|
|Stroke||70.6 mm (2.78 in)|
|Displacement||498 cc (30.4 cu in)||599 cc (36.6 cu in)||749 cc (45.7 cu in)|
|Power||32 hp (24 kW) @ 6,800 rpm||40 hp (30 kW) @ 6,600 rpm||50 hp (37 kW) @ 6,400 rpm|
|Torque||29 ft·lbf (39 N·m) @ 5,000 rpm||36 ft·lbf (49 N·m) @ 5,000 rpm||43 ft·lbf (58 N·m) @ 5,000 rpm|
|Top Speed||87 mph (140 km/h)||99 mph (159 km/h)||109 mph (175 km/h)|
|Curb Weight||452 lb (205 kg)||463 lb (210 kg)||463 lb (210 kg)|
|Gross Weight Rating||881 lb (400 kg)|
|Alternator||Bosch 12 V • 180 Watts|
|Spark Plugs||Bosch W230T30 / Champion N7Y|
|Fuel Tank||4.7 US gal (18 l; 3.9 imp gal) or 6.3 US gal (24 l; 5.2 imp gal)|
|Tires||3.25x19 front • 4.00x18 rear|
|Rims||1.85x19 front • 1.85x18 rear|
The /5 models came with an electric starter and also retained the outward-swinging kickstart lever, connected to the input shaft on the back of a four-speed gearbox similar to the one on the /2.