In 1958 the Szczecin motorcycle factory in presented a prototype of a three-wheeled cargo motorcycle based on the Junak M07. This vehicle, the B20, had a load capacity of 300 kg. The wooden cargo box, located at the rear, was equipped with bars and a canvas cover. Drive to the rear wheels was transmitted through a cylindrical differential. The construction of the cargo system allowed the vehicle to be transformed into an ordinary motorcycle.
In 1959, a modernized B20 prototype was built based on the M10 model. After road tests, the tricycle showed a few minor construction problems - the frames cracked as they were too rigid, and more troublesome were the drive chains, which lasted only 5000 km. The rims of the rear wheels were also not very durable, and broke after only 500 km. The rear brakes were good in the dry, but it proved necessary to seal them, because they suffered when wet.
Otherwise, the motorcycle drove very well, with a slight oversteer when empty. It was approved for production after minor design adjustments, use of chain guards and reinforcement of wheel discs. Production began in late 1960 or early 1961.
Technical description, 1960 production version
Type S03 engine, four-stroke as fitted to the Junak m10. The electrical installation was changed, and flashing indicators were mounted on the sides of the cargo box.
Spark plug, with m14 x l.25 thread, with a heat value of 225 (Bosch).
Drive transmitted to the rear axle is a single-row roller chain with dimensions of 5/8" x 9.95 x 10.16, with 82 links. Gear ratio 1.47 (17/25). The axle is equipped with a cylindrical differential with six satellites filled with oil (0.5 l). Drive transmitted through universal joint at the differential.
The main frame was that of the M10 motorcycle with the addition of a frame for the trailer, built on C-profile stringers.
Front suspension by telescopic fork, with coil springs and double-acting shock absorbers. Front wheel travel 150mm. Independent suspension of the rear wheels, on single transverse wishbones, with a semi-elliptical seven-leaf spring placed transversely.
Spoked front wheel. Rim size 1.85x19". Tube tyres, size 3.50-19". Disc rear wheels, pressed from steel sheet with 3.5x;12" rims and 5.20-12" tube tyres.
Mechanically actuated, independent, drum brakes. The rear (foot) brake, acting on two wheels, had the option of locking the pedal with a pawl to act as a parking brake.
Handlebar made of steel tube, attached to the upper fork clamp.
Internal dimensions of the cargo box 1260 x 1300 x 300. Height of the loading space with arches and sheets 850 mm, loading area 1.7 m2.
The motorcycle weighed 320 kg and had a fairly large load capacity of 300 kg. Fuel consumption was 5.7 l/100 km, and the top speed was 75 km/h.
Source: Junak.net Archive
