BMW /5 motorcycles

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 Black BMW R75/5
BMW R75/5
 Red BMW R60/5
BMW R60/5 (with BMW R80GS behind)

The BMW R50/5, R60/5, and R75/5 form a range of boxer twin motorcycles that were manufactured in Berlin, Germany, by BMW from 1970. Having electric starting and telescopic forks, the "slash-5" series was a significant advance over BMW's earlier rather utilitarian motorcycles, and the new bikes appealed to the emerging market for recreational motorcycles.

History[edit]

Closeup of BMW roundel badge on a part-painted and polished chrome fuel tank side panel
R75/5 tank roundel
 Black BMW R75/5
BMW R75/5 with "toaster" side-panels

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).[1] 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 the “long-wheelbase” (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.[2]

By the 1960s, motorcycles as a form of "cheap transport" were being abandoned by post-war consumers who could now afford a car; but the motorcycle market was revolutionised by a new kind of customer who wanted a bike for fun and recreation. Accordingly, production 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[when?] was the completion of the 500,000th BMW motorcycle in the history of the company.[2]

In 1974, BMW introduced the “/6” models, which offered some advances, such as a front disc brake, more modern instrumentation, and a five-speed transmission. The single disc brake was a hybrid cable/hydraulic system, whereby a cable from the handlebar lever actuated the master cylinder underneath the fuel tank. The “toaster” tank was dropped.

Technical Data[edit]

Top-down view of a black R75/5 showing that the cylinders which protrude out of each side of the bike are not directly opposite each other
Boxer engine showing offset cylinders

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.[3] 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) 110 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
 Red BMW R75/5 motorcycle fitted with panniers, parked on grass by a lake with a city in the background
BMW R75/5 with pannier

Last of the BMW kick starter[edit]

All /5 models had both an electric starter and a kickstart pedal.[4] Kickstarts were discontinued on some subsequent models, but kickstarts remained intermittently present up to model year 1980.

See also[edit]

References[edit]

  1. ^ [http://www.eecs.umich.ed.
  2. ^ a b Forty Years of BMW Motorcycle Production in Berlin-Spandau
  3. ^ Richard Backus (November–December 2009). "10 Days with a 1973 BMW R70/5". Motorcycle Classics. Archived from the original on 8 November 2009. Retrieved 2009-11-11. 
  4. ^ Falloon, Ian (2003). Original BMW Air-Cooled Boxer Twins 1950-1996. MotorBooks International. ISBN 978-0-7603-1424-1. 

External links[edit]