BMW R 51 / 3
Number sold 18.420
Price 2.750,- DM
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| Internal Designation | 252 / 1 |
| Engine type | four-stroke two-cylinder flat-twin |
| Bore/stroke | 68 x 68 mm |
| Cubic capacity | 494 cm3 |
| Max power | 24 PS 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 |
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| Power transmission | |
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| 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 sidecar 4,75 : 1) |
| Bevel/crown wheel | 9 / 35 teeth (with sidecar 7 / 32) |
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| Electrical system | |
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| Alternator | Noris 6 Volt L 45/60 L |
| Ignition | magneto ignition |
| Spark plugs | Bosch W 240 T 1 |
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| Suspension | |
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| 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 |
| Tyres front | 3,50 x 19 |
| Tyres 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) |
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| Dimensions and weights | |
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| Length x width x height | 2130 x 790 x 985 mm |
| Wheel base | 1400 mm |
| Tank capacity | 17 l |
| Unladen weight, full tank | 190 kg (with orig. BMW sidecar 320 kg) |
| Load rating | 355 kg (with orig. BMW sidecar 600 kg) |
| Fuel consumption | ca. 4,5 l / 100 km |
| Oil consumption | ca. 0,7l / 1000 km |
| Top speed | 135 km/h (with orig. BMW sidecar 95 km/h) |
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