From BMW Tech
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For the 1970 model year, BMW entered the age of modern motorcycles with three new BMW models having engine capacities of 500 cc (R50/5), 600 cc (R60/5), and at the top of the line 750 cc (R75/5). The R75/5 was one of the fastest production motorcycles of the time, topping out at 109 mph (175 km/h). The "slash-5" series came out just in time to meet the rising demand for sport bikes. All so-called "slash-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 Motorcycle fork, kick starters, 6 volt electrical systems, antiquated brakes, and frames descended from pre-war BMWs for use with sidecars.
The new, “Slash-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), nearly the lightest 750 cc bike of the era. These motorcycles were (and are) extremely reliable. It was (and is) not uncommon to encounter BMW "slash-5" motorcycles that have never been through a complete overhaul and have well over 100,000 miles (160,000 km). Such endurance was not common for the era.
Model year 1972 saw the introduction of the 4 US gallon (15 liter) “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 wheel base” 1973½ “LWB” models. This improved handling and enabled a larger battery to be installed behind the engine while retaining the kick starter.
In 1974, BMW introduced the “Slash-6” models , which offered numerous improvements, most notably disk front brakes, more and better instrumentation, and a five-speed transmission. The fabled “toaster” tank, however, was dropped.
The slash-5 models are air-cooled, four-stroke, Flat-twin engines with hemispherical Combustion chamber. The engine is built around a one-piece (and very strong) 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 C of G 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 slash-2 models, the slash-5 models are equipped with Motorcycle fork, 12-volt Alternator and electrics, and standard tachometer and turn signals.
|R 50/5||R 60/5||R 75/5|
|Bore||67 mm||73.5 mm||82 mm|
|Displacement||498 cc||599 cc||749 cc|
|Power||32 hp (24 kW)||40 hp (30 kW)||50 hp (37 kW)|
|Torque||29 lb·ft (39 N·m)||36 lb·ft (49 N·m)||43 lb·ft (58 N·m)|
|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 vehicle weight rating||881 lb (400 kg)|
|Alternator||Bosch 12 V • 180 Watts|
|Spark Plugs||Bosch W230T30 / Champion N7Y|
|Fuel Tank||4.7 or 6.3 US gallons (18 or 24 litres)|
|Tires||3.25x19 front • 4.00x18 rear|
|Rims||1.85x19 front • 1.85x18 rear|
Last of the BMW kick-starters
The slash-5 models came with an electric starter but the new series (along with the first few of the next series, the /6) retained the kick-starter, still mounted on the back of a four-speed gearbox similar to the one on the /2. But kick-starting this larger engine, still with the outward swinging BMW kick-starter, was now even more of an acquired art than it had been before. Most people found they could only do it with the machine on one or other of the stands, standing on the left side of the machine and using the right foot. A few put the motorcycle on the center-stand and stood left-footed on the cylinder head - even so, it was impossible to get much of a swing. With regular tuning and a well-maintained battery the kick-starter gets little use and this is the ideal situation.