MZ BK350
The MZ BK 350 (BK = Boxer-Cardan) is a motorcycle model from the VEB Motorradwerk Zschopau, which was produced from 1952 to 1959; until 1956 under the name “IFA BK 350”.
History
As early as 1946, functional models of the later BK 350 were developed and tested at Bark based on DKW models. At the Leipzig Spring Fair in 1951, the BK 350 was presented as a DKW two-cylinder model. However, the start of series production was delayed until the end of 1952.
The BK 350 was the first new design from the former DKW factory after the end of the war and was awaited with great international interest due to its special design (boxer engine and cardan drive). At the start of series production, it ran under the name of the now state-owned GDR vehicle construction association IFA.
Building on the positive experience of the ES series, the development of a full swing chassis called the BK 351 was completed in 1958 and a few functional models were built. Since it was decided at the same time to significantly increase the number of ES models, which were less expensive to produce, production of the BK 350 ended in 1959.
Chassis
The frame is a welded double-loop tube frame with connection points for a sidecar (which can be connected on the right or left). It is reinforced with triangular gussets on the steering head. At the rear, the BK 350 has straight-line suspension with 50 mm travel, at the front a telescopic fork with 148 mm travel, the integrated steering damper can be adjusted with a star grip screw on the upper clamp head. The BK 350 has quick-release axles at the front and rear, and the two internal shoe brakes have a diameter of 200 mm.
Drive
The BK 350 is powered by a slot-controlled two-cylinder two-stroke boxer engine with a total displacement of 343.5 cm³, initially with 15 HP and from 1957 with 17 HP. The inspiration for this type of engine was development work carried out at the end of the Second World War at the DKW headquarters in Zschopau to produce a short-stroke boxer engine as a starting unit for aircraft.
According to the manufacturer MZ, the division of the displacement into two cylinders was chosen because of the high flushing losses at displacements greater than 250 cm³ with three-channel flushing. Due to the difficult availability of drive chains at the time, a cardan drive was chosen to transmit power to the rear wheel. For these reasons, a boxer engine with a longitudinal crankshaft was designed. On the drive shaft that protrudes to the rear is a sheet-metal-encapsulated rubber joint in which the cardan shaft is mounted so that it can slide (to compensate for the length of the suspension). The angular movement that occurs on the rear wheel drive when the vehicle is deflected is absorbed by a universal joint that is also sheet-metal-encapsulated.
Electrical system
The BK 350 has a 6 V DC alternator with a nominal output of 60 W. The associated regulator is housed with the alternator under the front engine housing cover. The battery is on the clutch side under the side panel. This is also where the electrical fuses and the on-board tools are located. The headlight is a surface-mounted headlight with a diameter of 160 mm. It is equipped with a 6 V/35 W + 35 W Bilux bulb. The speedometer and ignition lock are built into the headlight housing.
Sidecar
The BK 350 is designed for operation with a sidecar, which is connected to three points on the BK frame. The sidecar offered ex works was manufactured by Stoye-Fahrzeugbau-Leipzig.
Model update
From 1957, the MZ ES 250, which was produced at the same time by MZ, was sold with an increased output of 14.25 HP (10 kW). Since the difference to the BK 350 would have been relatively small, the engine power of the BK was increased to 17 HP (13 kW) at the same time. With the improved intake and exhaust damping (intake and exhaust side), the noise emissions were noticeably reduced.
Off-road sports
The BK 350 was also used in off-road sports. For example, in 1953 a three-man club team started on the BK 350 in the 28th International Six-Day Race in Czechoslovakia Gottwaldov. The machines were equipped with the necessary off-road tires and protective bars for the headlight.
Manufacturer: VEB Motorradwerk Zschopau (MZ GmbH)
Assembly: Zschopau (GDR)
Years of production: 1952—1959
Production: 41,163 units
Length: 2150 mm
Width: 800 mm
Height: 1000 mm
Engine: 2 cylinders; 343 cc
Power: 17 HP
Max speed: 115 km/h
Weight: 142 kg
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