Junak Motorcycles

Junak M14 350cc OHC Iskra

A new machine was developed in 1961, designed to be lighter and more powerful than the M10. An order for the development of a twin-cylinder, four-stroke engine to power it was placed with ZSM No. 1.

In October 1961, a dimensional drawing of the engine was sent to SFM to begin work on the motorcycle chassis in earnest. Three preliminary designs were prepared: with a push-pull timing system and two with a chain-driven timing system (in the first, the chain was routed between the cylinders, in the second, the chain was placed on the left side of the engine). The chosen design, by Eng. Leszek Ornaf, was completed in December 1962. The twin unit with the designation S132 LO had a capacity of 350 cc and a chain-driven overhead camshaft. It was possible to increase its capacity to 500 cc.

When designing the new unit, the experience gained from redesigning the SO3 engine was taken into account and the most modern motorcycles of Western and Japanese production were carefully analyzed. Single, air-cooled cylinders were used, completely replaceable thanks to the symmetrical fins. It was possible to create a single-cylinder version with a capacity of 175 cc and (unofficially) a 4-cylinder automotive version. Careful attention was been paid to the cooling of the cylinders, opening them slightly apart and designing substantial fins around the valves. The combustion chamber hemi-spherical shape, allowing an improved burn.

At this time Honda reportedly introduced a similar solution. It was envisaged that the M14 castings would be die-cast aluminum, and the cylinders would also of aluminum with chrome-plated cylinder walls. The prototype, however, used cast iron cylinders. The camshaft located in the head was hollow, and at its end there was an ignition device adapted from Syrena. The valve rocker arms in the prototype were mounted on needle bearings.

Since Junak's S130 engine weighed 63 kg, it was projected that the S132 would not exceed 50 kg. The prototype weighed only 47 kg. In the 4-speed gearbox, two threads were used, in the Junak M10 there were three (clutch, lower and output, in the M14 only the clutch and output were left). The S132 had a common oil circuit for the engine, clutch and gearbox. The S132 was relatively straightfoward to manufacture and did not require additional machine tools. It was expected to be cheaper to produce than the S03 and S130.

Projects S132 l01 and S132 l02 were created. In the latter, the axis of the drive cat of the chain gear coincided with the axis of rotation of the swingarm, and the clutch was moved to the axis of the crankshaft. In 1964, the construction of prototypes began.

Meanwhile, SFM was in full swing working on the M14 chassis under the supervision of the chief designer, Eng. Andrzej Kazuba. Among the design team, Eng. Lech Nowosad. He designed the motorcycle in such a way as to ensure comfortable riding even over long distances. From the model motorcycles, plans and photos found in SFM, he calculated the optimal dimensions of the machine, the distance between the seat, footrests and handlebars.

The M14's chassis consisted of a single welded tubular steel cradle frame. The front wheel was suspended on a short push arm. The M14, following the example of the most modern machines at that time, had an enclosed silhouette, and the styling of the bodywork was developed together with the Warsaw Institute of Industrial Design. Two prototypes were made in 1964, painted green to distinguish them from black or cherry-red M10s

In 1964, the production of shafts and steering mechanisms began to be taken over from FSO in Warsaw and FSC in Starachowice. The management of SFM was deluded that it would be possible to combine the production of both ranges and agreed to complete the M14 tests. Zbigniew Konieczek, working in the testing department at the time, remembers that the motorcycles were extremely fast, reaching speeds of up to 145 km/h. The press dubbed the new motorcycle "Iskra". Despite the use of modern solutions, the motorcycle required refinement. Pushing wishbones did not provide stable front wheel guidance, which was particularly noticeable when braking, but this defect could not be removed.

Work on the M14 model was never completed. Only two prototypes of the S132 l01 engine were made, but they were never fitted to motorcycles. The M14 prototype is located in the Factory Museum of the Polmo Car Mechanism Factory in Szczecin.



Engine type:, 4-stroke in-line twin-cylinder.

Capacity 350 cc, air-cooled

Valve timing: OHC, two valves per cylinder

Compression ratio: 8.5-9:1

Maximum power: 21-26 h.p. ( 15-19 kw) at 6000-7000 rpm

Maximum torque: 32 Nm at 3200-4200 rpm

Fuel supply: 2 horizontal GM 26 S1 carburettors with a common float chamber (also given as GM 26 M1)

Clutch: multi-disc, wet

Gearbox: 4-speed

Transmission to the rear wheel: chain

Chassis - frame: single, welded steel cradle

Suspension: front - push arm; rear - trailing arm

Brakes: drum

Tyres: 3.25x18

Weights and dimensions

Weight in running order: approx. 138 kg

Wheelbase: 1348 mm

Dimensions (height/length): 945x approx. 1944 mm

Fuel tank capacity: approx. 13 l


Maximum speed: 145 km/h acceleration 0-100 km/h: no data

N.B. Some details omitted from original.

Source: Junak.net Archive