1939 - Start of production of JAWA 250 Duplex motorcycle PDF Print E-mail
Written by Dr Amit Chatterjee, SM   

JAWA 250 Duplex Blok

Two stroke air-cooled single cylinder with inverted scavenging * Displacement 248 cc (bore and stroke 68 x 68 mm) * Engine power 6.6 kW al 4000 r.p.m. * Compression ratio 6 to 1 * Four-speed gearbox with foot control bolted to the engine forming a block * Multi-plate clutch in oil bath * Closed duplex frame made with stamped steel sections * Rigid rear wheel suspension * Parallelogram front fork with coil spring suspension * Weight 115 kg * Maximum speed 100 km/hour * Average fuel consumption 3 to 3.5 litres per 100 km

Before the outbreak of the Second World War the factory had come with one more novelty - the JAWA Duplex-Blok appeared on the market. It was a two-fifty based on the familiar two-stroke JAWA 250, but with the power unit reconstructed so much that it has to be described as a new model.

The "Duplex-Blok" - four-speed gearbox
The "Duplex-Blok" - four-speed gearbox controlled by gear change pedal is joined with the engine, though it’s a separate block
The "Duplex-Blok" engine
The "Duplex-Blok" as seen from the left side
The gearbox was, namely, joined with the engine, though its was a separate part (block), primary drive was by duplex chain. The engine was also changed, it was made "square" (68x68), displacement 246cc. Its power output was 6.6 kw (9HP) at 4000 r.p.m. and 6 to 1 compression ratio. The cylinder barrel was a special grey iron casting, the cylinder head of light alloy, ignition by JAWA flywheel magneto, Amal or Grätzin carburetter. The multi-plate clutch in oil bath coupled to engine with a four-speed gearbox controlled by gear change pedal.

The JAWA 250 "Duplex-Blok"The frame and front fork were of the well-proven pressed type reinforced partly compared to the JAWA 250 model. The two-piece rear mudguard and detachable spindle made wheel removal considerably easier. Knee grips were standard equipment. The tyres were of 3.25 - 19 size.

Machine weight was approx. 115kg, maximum speed 100 km/hour, average consumption 3.5 litres per 100 km. JAWA put on the market in 1939, 900 Duplex models, another 100 units were assembled after the war. Worth mentioning are prototypes of the JAWA 175 Duplex-Blok, their turn, however, never came. The Duplex- Blok was the factory's pre-war swan song. But it foreshadowed what was to originate at JAWA later.

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