Junak B20 Make Model | Junak B20 | Year | 1960-65 | Production | 2500 | Engine | Four stroke, single cylinder, OHV | Capacity | 349 cc / 21.3 cub. in. | Bore x Stroke | 75 x 79 mm | Compression Ratio | 7.0:1 | Cooling | Air/Oil cooled | Lubrication | Dry-sump | Ignition | Magneto | Battery | 14 Ah, 6V | Dynamo | 45 W | Starting | Kick-start | Clutch | Multi-plate clutch with cork inserts working in an oil bath | Max Power | 14 kW / 19 hp @ 6000 rpm | Max Torque | 27.5 Nm / 2.8 kgf-m / 20.3 ft-lb @3800 rpm | Transmission | Four-speed constant-mesh | Final Drive | Chain | Gear ratios | 1st 3.04 / 2nd 1.97 / 3rd 1.29 / 4th 1.00:1 | Frame | Double, cradle-type, welded throughout of tubing, provided with holders for side car mounting. | Front Suspension | Fork with coil springs telescopic shock absorbers | Rear Suspension | Independent rear wheel suspension on single wishbone , cooperating with 7- leaf spring positioned transversely; | Front Brakes | Full hub width, of expander shoe type, hand operated | Rear Brakes | Full hub width, of expander shoe type, foot operated | Wheels | Wire type, with full width hubs made of light alloy, interchangeable (also with side-car wheel). Both wheels with quick-detachable spindles | Front Tyre | 19 in | Rear Tyre | 12 in | Front Rim | 89 mm / 3.5 in | Rear Rim | 89 mm / 3.5 in | Trail | 72 mm / 2.8 in | Dimensions | Length: 3055 mm / 120.3 in Width: 1420 mm / 55.9 in | Dimensions of Box (internal) | Length: 1360 mm / 53.5 in Width: 1260 mm / 49.6 in Height: 300 mm / 11.8 in | Rear Track | 1100 mm / 43.3 in. | Wheel Base | 2010 mm / 79 in | Seat Height | 755 mm / 29.7 in | Ground Clearance | 170 mm / 6.7 in | Wet Weight | 320 kg / 705.5 lbs | Load Capacity | 300 kg / 661.4 lbs | Fuel Capacity | 17 l / 3.9 US gal | Average Consumption | 5.7 l/100 km / 17.5 km/l / 41.3 mpg | Top Speed | 75 km/h / 46.6 mph | Source | Article by T. Tomaszewski in ?Świat motocykli” 2003. | Junak B20, a three-wheel transport version of Polish Junak motorcycle, based on serial M10 model. From 1960 to 1965 about 2500 units were built, 153 of them were exported. Very few B20 are preserved.
Junak motorcycle suffered from poor reliability, when it was introduced, so in 1958 development and construction office at SFM (Szczecin Motorcycle Factory) started to work on base model modifications. Another task was to adjust the motorcycle to a wider range of practical applications. The idea was to build a three-wheel transport version for small business. In very next year two prototypes were shown: B20 with goods carriage box supported by two rear wheels, and B21with goods carriage box in the front, with two front wheels and one rear. Both prototypes were based on elements of serial M10 Junak motorcycle. The B20 proved to be superior to B21, with greater top speed (75 km/h when compared with 60 km/h) and possibility to carry 300 kg of load, when the own weight of the three-wheel vehicle was 320 kg. Fuel usage was about 5,7 l/100 km. Carriage box's dimensions were 1260 x 1360 mm and 300 mm high, with swing-opened rear side, tarpaulin on four posts and two independently sprung 12” wheels. Latch brake was added to ensure the heavy vehicle will not roll down the slope, when parked. This was an attractive design for shopkeepers, farmers and post office workers; post office was later one of recipients of B20 production. From an article by T. Tomaszewski in ?Świat motocykli” 2003. |