BMW R51/3
  BMW R 51/3

BMW R 51 / 3
      1952 BMW R51/3 at Iron Horse Motorcycles, Tucson, AZ
Date 1951 - 1954

Number sold 18,420

Price 2,750.- DM

   $983.81 in 1952 dollars
$7,964.67 in 2010 dollars


Engine

Internal designation 252 / 1
Type four-stroke, two-cylinder, flat twin (boxer)
Bore/stroke 68 x 68 mm
Cubic capacity 494 cm3 / 30 inches3
Max power 24 HP at 5800 U /min
Compression ratio 6.3 : 1
Valves per cylinder ohv
Carburation system 2 carburettor Typ Bing 1/22/41-1/22/42 or 1/22/61-1/22/62
Engine lubrication forced-feed lubrication
Oil pump gear pump

 
Power transmission

Clutch single discs, dry
Number of gears 4
Shifting foot shifting (+ auxiliary manual lever on the gear block)
Gear ratios 4.0 / 2.28 / 1.7 / 1.3 (bis Ende 1951: 3.6 / 2.28 / 1.7 / 1.3)
Rear wheel ratio 1 : 3.89 (with original BMW sidecar: 4.75 : 1)
Bevel/crown wheel 9 / 35 teeth (with original BMW sidecar: 7 / 32)

 
Electrical system

Alternator Noris 6 Volt L 45/60 L
Ignition magneto ignition
Spark plugs Bosch W 240 T 1

 
Suspension

Designation 251/3 (1951), 251/4 (1952/53), 251/4 (1954)
Type of frame twin-loop steel tubular frame
Front suspension telescopic fork
Rear suspension telescopic fork
Wheel rims deep-bed 3 x 19
Tires front 3.50 x 19
Tires rear 3.50 x 19
Brakes front drum brake, Ø 200 mm (1952: Duplex, 1954: full hub)
Brakes rear drum brake, Ø 200 mm (1954: full hub)

 
Dimensions and weights

Length x width x height 84 x 31 x 39 inches / 2130 x 790 x 985 mm
Wheel base 55 inches / 1400 mm
Tank capacity 4.5 gals. / 17 liters
Unladen weight, full tank 419 lbs. / 190 kg (with original BMW sidecar: 705 lbs. / 320 kg)
Load rating 783 lbs. / 355 kg (with original BMW sidecar: 1,322 lbs. / 600 kg)
Fuel consumption 52 MPG (ca. 4.5 liters / 100 km)
Oil consumption ca. 0.7l / 1000 km
Top speed 84 MPH / 135 km/h (with original BMW sidecar: 59 MPH / 95 km/h)