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.