Junak M07
Junak M07/B21 (prototype)
Junak M10
Junak M10 with WB1 Sidecar
Junak M10/B20
Work on a new type of heavier motorcycle, equipped with a four-stroke engine, began in 1952 at the Design Office of the Automotive Industry in Warsaw. The creators of this vehicle were Eng. K. Wójcicki (engine) and Eng. S. Porazinski (chassis). Initially, it was planned to use an engine with a displacement of 0.500 litre, but in the end it was decided that it would be a volume of 0.350 litre. The prototype of the motorcycle, which was named Junak, made with the help of the Warsaw Motorcycle Factory, was presented at the 10th Anniversary Exhibition in Wrocław in August 1954. In those years Junak was a very modern motorcycle. The 12.5 kW (17 hp) overhead valve engine, together with the four-speed gearbox, ensured good vehicle performance.
A rigid frame with a closed structure and suspension of both wheels on spring elements, with oil damping, guaranteed proper handling of the motorcycle in all road conditions. ' There were problems with the localization of Junak's production. Finally, it was decided that the engine would be manufactured at Wytwórnia Sprzętu Mechaniczne in Łódź, while the remaining units and assembly at Szczecinskie Zakłady Wyrobów Metalowych, which later changed its name to Szczecin Fabryka Motormotorcycles.
Engine - Type 803, spark ignition, four-stroke, vertical, rigidly mounted at four points of the frame. Bore 75 mm, stroke 75 mm. Number of cylinders l. Displacement 0.349 litre.
Compression ratio 6.8. Maximum power 12.5 kW (17 hp) at 5500 rpm. Maximum torque 24.0 Nm (24.5 kGm) at 4000 rpm.
Engine block, cast in light alloy, vertically split, common with the gearbox casing. Ribbed cast iron cylinder. Ribbed head made of light alloy casting. Strain relief fixed in the head. Forged, split crankshaft. Carbon steel counterweights, alloy steel trunnions. Crankshaft supported on three roller bearings. Light alloy piston with two sealing rings and one wiper ring. Forged connecting rod, double-row roller bearing in the foot. Floating piston pin. Overhead valve timing, tappet. Two shafts with cams, driven from the crankshaft through a toothed gear. Valves set at 90°. Diameter of the intake valve disc 43 mm, exhaust valve 40 mm. Intake valve open 3rd before TDC, close 75° after TDC, exhaust valve open 85° before TDC, close 45° after TDC.
Circulating lubrication, under pressure. Double gear oil pump. Oil tank in the engine block, around the gearbox chamber (so-called dry sump). Mesh oil filters, placed in the tank. Forced air cooling.
Power supply: Amal 276/117/R horizontal carburetor, throat diameter 25.4 mm. Air filter, with a metal mesh filter element, placed under the saddle between the side boxes. Suction noise muffler. Mesh fuel filter, located in the tap of the fuel tank.
Electrical system - Nominal voltage 6 V. Positive earth. Ignition from a spark gap, type m 3 304 or IKA-ZS-3, mounted outside the engine, at the front. Static ignition setting 13° before TDC. Centrifugal" ignition advance angle adjuster with a range of 24°.
Spark plug, M14X1.25 thread, 225 calorific value (Bosch). DC generator, type R6 45-DIN 72417 or P9a, 45 W, located in the engine block behind the cylinder. Generator regulator type RSC/45 6b or RG9a. 6 V lead battery, 14 Ah capacity. Headlight, optic diameter 160 mm, with high beam, symmetrical dipped beam and position light. Rear lamp with position light and stop light. Sound signal, type BFSK. or PAL 6V, fixed to the frame below the tank.
Drive system - Friction clutch, wet, four-plate, with cork linings (20 inserts in the disc), with a central helical pressure spring. Lever-operated mechanism. Driven by the crankshaft, transmitted to the clutch by a 3/8" XX 15.95X6.35 86-link double roller chain. Sliding chain tensioner. Gear ratio 2.335 (56/23). Four-speed gearbox. Constantly meshing gears. Gear ratios for individual gears: Ib-3.04, IIb-1.97, IIIb-1.296, IVb-l.0 Gear shifting with a foot lever located on the left side of the engine Transmission of the drive to the rear wheel with a single-row roller chain, dimensions 5/ 8"x9.95x10-16, 102 links. Gear ratio 2.40 (48/20). Adjusting the chain tension with two two-way tensioners, located at the ends of the rear swingarm arms.
Chassis - Cradle frame, closed, double, welded from steel pipes with an elliptical cross-section. Two angular contact ball bearings embedded in the head tube. Front wheel suspension on a telescopic fork with coil springs and double-acting hydraulic shock absorbers. Fork shelves: upper and lower. Front wheel travel 146 mm. Rear wheel suspension on trailing arm, with two spring elements, with coil springs and double-acting telescopic shock absorbers. Rocker arm welded from steel tubes. Rear wheel travel 96mm. Spoked road wheels, rims sized 1.85X19", made of steel. Tube tyres, sized 3.50-19".
Braking and Steering - Mechanically actuated, independent, drum brakes. Brake drums made of pressed pressed metal. Internal diameter of brake drums 200 mm, width of friction linings 25 mm. Hand brake and foot brake actuated by Bowden cable. Steel tube handlebars attached to the top of the fork. The handles of the clutch and hand brake levers are integral with the steering wheel, the levers are made of pressed steel. On the left side of the steering wheel there is a lever controlling the depressuriser, on the right the air throttle lever. The speedometer is driven by a flexible shaft from the rear wheel.
Bodywork - Shallow mudguards, pressed from sheet steel. The front mudguard is attached to the movable part of the fork. The fuel tank is welded from steel stampings, with a luggage carrier made of pressed pressed metal fixed on it. Three-position fuel tap. Sofa saddle, double, latex cushion, leather cover. In the rear part of the frame, there is a storage compartment for the battery, an air filter box on its left side, and a toolbox on the right.
Riders's footrests are adjustable, with rubber covers. Folding passenger footrests with rubber covers. Central stand welded from steel pipes, suspended on the lower beams of the frame. Side stand on the left. Partial chain guard, with a fixed part attached to the engine on the right side of the motorcycle.
Dimensions - Wheelbase 1425 mm. Total length 2180 m, width 730 mm, height 1020 mm. Front seat height 760 mm, rear seat height 800 mm. Ground clearance 170mm.
Weight - Motorcycle 165 kg. Permissible load 190 kg. Permissible total weight 355 kg. Permissible load on the front wheel 125 kg, rear wheel 230 kg.
Capacities - Fuel tank 17 drn3 (including 3 litre reserves), engine lubrication system 3.0 litre, clutch chamber 0.5 8m 3, gearbox 0.1 litre.
Operational data - Top speed 115 km/h. Fuel consumption 3.5-4.0 litre/100 km. The smallest turning diameter is 4.2 m. Travel time for 400 m from a standing start is 21.2 s.
Tyre pressure front 0.14 MPa (1.4 kGm/cm2), rear 0.18 MPa (1.8 kg/cm2).
The constructors of the Szczecin Motorcycle Factory have developed a contraction of three-wheeled, cargo, variants of the Junak M07 motorcycle. The prototypes were publicly presented in the summer of 1958 at a factory exhibition in Szczecin. The version marked B21 had a cargo bed at the front and was equipped with small steered front wheels. The load capacity of this vehicle was 300 kg. The drive system was taken from the M07 motorcycle, only the overall gear ratio was changed, which limited the maximum speed to 60 km/h. The front part of the vehicle frame was permanently connected to the motorcycle frame. In 1959, another prototype was built, already based on the Junak M10 model. Serial production of this vehicle has not started.
Engine - Type S03, spark ignition, four-stroke. Data as in the Junak M07 motorcycle.
Electrical system - Data as in the Junak M07 motorcycle, with the following changes: two headlights.; with an optical system diameter of 160 mm, with high beam, symmetrical low beam and position lights.
Drive system - Data as in the Junak M07 motorcycle.
Leg system - The frame of the vehicle consisted of the frame of the M07 motorcycle, supplemented in the front part with the load box frame and the front suspension. Suspension of the front wheels is independent, on single transverse wishbones, cooperating with a semi-elliptical leaf spring placed transversely. Rear wheel suspension on trailing arm, with two spring elements, with coil springs and double-acting hydraulic shock absorbers. Rear wheel travel 96mm. Front disc wheels, pressed from pressed metal. Rims 3.50X12". Tube tyres 5.20-12". Spoked rear wheel. Rim size 1.85X19*'. Tube tyres, dimensions 3.50-19".
Braking System - Mechanically actuated, independent, drum brakes. Front brake (hand brake) acting on the two front wheels. Rear (foot) brake acting on the rear wheel.
Steering system - Motorcycle steering wheel made of steel tubing, connected with steering rods to the steering knuckles of the front wheels. Clutch and handbrake levers pressed from sheet steel.
Body - Load box with a wooden structure. Two headlights and a pressed metal bumper were attached to the front wall. Fuel tank welded from sheet steel stampings. A trunk, pressed from sheet metal, is attached to the tank. 3-position fuel tap, 2-seat bench seat, porous rubber cushion, dermatoid cover. In the rear part of the motorcycle frame, there is a battery compartment, an air filter on the left, and a tool compartment on the right. Adjustable riders's footrests with rubber pads. Passenger footrests fold up, with rubber pads. Partial drive chain cover. The fixed part is attached to the engine, the movable part to the swingarm. Shallow rear mudguard. Lower exhaust system, mounted on the right side of the vehicle.
Dimensions - Wheelbase 1600 mm, front track 1100 mm. Total length 2750 mm, width 1300 mm, height 1100 mm. Front seat height 760 mm, rear seat height 800 mm.
Weight - Own vehicle approx. 300 kg. Load capacity 300 kg.
Capacity - Fuel tank 17 litre, engine lubrication system 2.4 litre. Clutch chamber 0.5 litres, gearbox 0.4 litre.
Operating data - Top speed 60 km/h. Fuel consumption 5.5 dm>/100 km.
A relatively long time had passed since the development of Junak's construction until the launch of serial production and the process of modernization of the motorcycle had to begin. The changes concerned mainly the engine and chassis. The increase in the compression ratio and the use of a new carburetor made in Poland changed the characteristics of the engine. New full-hub brake drums were introduced in 1959, while deep mudguards and a modern headlight housing were used on 1960 models. In the same year, a new designation of the Junak M10 motorcycle was introduced. Regardless of the design development, the number of motorcycles produced increased year by year. In 1958, 2,800 Junaks were built, the following year 8,000 units, and in 1960 production reached 12,000 units.
Engine - Type 803, spark ignition, four-stroke. Data as for Junak M07, with the following changes: Compression ratio 7.0. Maximum power 12.5 kW (17 hp) at 6000 rpm. Maximum torque 27.5 Nm (28 kGm) at 3800 rpm. Power supply: horizontal carburettor, type Pegaz G26 Ul, with a throat diameter of 26 mm, with a starting device.
Electrical system - Data as for Junak M07, with the following change: Spark plug, with M14Xl.25 thread, with a thermal value of 175 (according to Bosch). The SP56 sound signal is located in the reflector housing.
Drive system - Data as for Junak M07.
Support system - Data as in the Junak M07 motorcycle, with the following changes: front wheel stroke 150 mm, rear wheel stroke 100 mm.
Braking and Steering - Brakes mechanically actuated, independent. Front and rear drum brakes, full hub. Light alloy cast brake drums with cast iron insert. Brake drum inner diameter 200 mm, brake lining width 40 mm. Hand brake and foot brake controlled by Bowden cables. The speedometer is driven by a flexible shaft from the rear wheel. Steel tube handlebars attached to the top of the fork. The handles of the clutch and hand brake levers form a whole with the steering wheel, the depressurizer lever and the light switch with the signal button are mounted on the left side, the air throttle lever (suction) is mounted on the right side.
Body - Deep mudguards, pressed from pressed metal. The front mudguard is attached to the movable part of the fork. Luggage carrier, pressed from pressed metal, is attached to the fuel tank. Three-position fuel tap. Double bench seat, porous rubber cushion, dermatoid cover. In the rear part of the frame, there is a storage compartment for the battery, an air filter on its left side, and a tool compartment on the right. Riders's footrests are adjustable, covered with rubber covers. Passenger footrests with rubber covers, fold up. Central stand, welded from steel pipes, suspended on the lower beams of the frame. Side stand on the left. Non-dismountable exhaust silencer, on the right side of the motorcycle.
Dimensions - Wheelbase 1417 mm, overall length 2200 mm, width 735 mm, height 1045 mm. Front seat height 790 mm, rear seat height 855 mm. The distance between the saddle surface and the riders's footrests is 560 mm. The lowest point from the road (central stand) 115 mm.
Weights - Own 193 kg. Permissible load 160 kg. Permissible total weight 355 kg. Permissible load on the front wheel 125 kg, rear wheel 230 kg.
Capacities - Fuel tank 17 litre, engine lubrication system 2.4 litre, clutch chamber 0.5 litre, gearbox 0.4 litre.
Operational data - Top speed 110 km/h. Fuel consumption 3.5-4.2 dnA 100 km. Travel time 400 m from a standing start 21.7 s. Tyre pressure: front 0.14 MPa (1.4 kG/cm2), rear 0.16 MPa (1.6 kG/cm2).
The Junak motorcycle frame was adapted accept a sidecar. In 1959, the Szczecin Motorcycle Factory developed and implemented a sidecar for a passenger, marked with the WB1 symbol. The road wheel used came from a Junak motorcycle and was suspended on a short push arm cooperating with a coil spring. The gondola, made of sheet steel, was equipped with a windshield with a celluloid window.
Engine - Type S03, spark ignition, four-stroke. Data as for the Junak M10.
Electrical installation - Data as for the Junak M10.
Drive system - Data as for the Junak M10.
Support system - Data as for the M10.
Braking and steering system - Data as for the M10.
Body - Data as for the M10.
Dimensions and weights - Data as for the M10.
Capacity and operating data (without a sidecar) - Data as for the M10.
Sidecar WB1
Trolley carrying system - A frame welded from steel pipes, adapted to a four-point connection with a motorcycle, equipped with two ball joints and two tubular struts. The wheel is suspended on a short push-arm, acting on a coil spring. Spoked road wheel, rim size 1.85X19". Tubular tyres, size 350-19". The sidecar had no brake. Trolley body - Gondola made of pressed metal, pivotally suspended in the front part of the frame, and in the back on two stretched rubber rings. The seat, covered with dermatoid, had a reclining backrest, behind which there was a luggage compartment. The sides of the gondola pattern are equipped with soft armrests. Entry step at the front of the mudguard. Windshield with curved celluloid glass. Tarpaulin cover covering the gondola pattern. Trolley dimensions and weights - Total length 1800 m, height 1120 mm. The weight of the trolley is 67 kg. Motorcycle with sidecar Dimensions and weights - Overall length 2195 mm, width 1490 mm, height 1120 mm. Wheelbase motorcycle-sidecar 1020 mm. The distance between the axis of symmetry of the motorcycle and the sidecar is 670 mm. Curb weight (combined: motorcycle-sidecar) 260 kg. Permissible total weight 470 kg.
Operating data - Top speed 85 km/h. Fuel consumption 4.5-6.0 cc / /l 00 km. Tyre pressure: front wheel 0.14 MPa --0.1.6 MPa (1.4-1.6 kg/cm2), rear wheel 0.18-0.20 MPa (1.8-2.0 kG/cm2) cm2), trolley wheels 0.14-0.15 MPa (1.4-1.5 kG/cm2).
In 1958, the Szczecin Motorcycle Factory presented a prototype of a three-wheeled cargo motorcycle based on the Junak M07. This vehicle, marked with the symbol B20, had a load capacity of 300 kg. The loading box with a wooden structure, located at the rear, was equipped with bars and a canvas cover. Drive to the rear wheels was transmitted through a cylindrical differential. The detachable construction of the carrying system allowed the vehicle to be transformed into an ordinary motorcycle. In 1959, a modernized B20 prototype was built based on the M10 motorcycle assemblies. The vehicle has been approved for production. Below is a technical description of the 1960 production version.
Engine - SOS type, spark ignition, four-stroke. Data as for the Junak M10.
Electrical system - Data as for the Junak M10, with the following changes: Spark plug, with M14Xl.25 thread, with a thermal value of 225 (according to Bosch). Flashing direction indicators, mounted on the sides of the cargo box.
Drive system - Data as for the Junak M10, with the following changes: Transmission of the drive to the rear axle with a single-row roller chain with dimensions -5/8"X X9.95XlO,li8, with 82 links. Gear ratio 1.47 (17/25). Roller differential with six satellites Drive shafts with flexible joints on the differential.
Chassis - The frame is the same as the M10 and the frame of the trailer. Longitudinal trailer frame, welded. C-profile stringers. Front wheel suspension on a telescopic fork with coil springs and double-acting shock absorbers. Front wheel travel 1.50mm. Suspension of the rear wheels is independent, on single transverse wishbones, cooperating 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 of pressed metal. Rims 3.5x12". Tube tyres 5.20-1.2".
Braking and Steering - Mechanically actuated, independent, drum brakes. The rear (foot) brake, acting on two wheels, had the option of locking the pedal with a pawl (at a standstill). Steel tube handlebar, attached to the top of the fork. Clutch and handbrake levers pressed from sheet steel.
Bodywork - as for the Junak M10, with the following additions: Cargo box of wood. The frame is made of wooden slats, the floor and walls are made of waterproof plywood. Opens at the rear. Tarpaulin cover with a rear opening, stretched on four steel tubular arches. Rear mudguards made of pressed metal, affixed to the cargo box.
Dimensions - Wheelbase 2010 mm, rear track 1100 mm. Total length 3055 mm, width 1420 mm. height without load 1550 mm. Internal dimensions of the cargo box 1260 x 1350 x 300 mm. The height of the cargo space with roll bars and sheets 850 mm. The surface of the cargo box is 1.7 m2. Height of the cargo tray 850 mm.
Weight - 320 kg. Load capacity 300 kg.
Capacity - Data as for the M10, with the following addition: differential gear 0.5 litre.
Operating data - Top speed 75 km/h. Fuel consumption 5.7 litre /100 km. Tyre pressure: front wheel 0.15 MPa (1.5 kG/cm2), rear wheels 0.13-0.20 MPa (1.3-2.0 kG/cm2).
Source: Polish History Archive
