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» Economics » BMW » Topics begins with B » BMW R 25/3

Page modified: Wednesday, July 13, 2011 08:45:51

The model R 25/3 is a motorcycle manufactured by BMW in the first half of the 1950er years.

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The predecessor BMW R 25/3 was the model BMW R 25/2, likewise with 9 KW (12 HP), Teleskopgabel and Geradweg Hinterradfederung her was provided not yet like the later models with rockers. From this differed R 25/3 (built starting from 1952) with more efficient Vollnaben-Bremsen, very similarly the large two-cylinder double-piston engine models with 500 ccm (BMW R 51/3) and 600 ccm (BMW R 67/2). Unfavorable the high weight of the machine was, compared to nevertheless somewhat the small achievement.

Design features

The double tube framework is welded made of steel tube with laterally attached balls for the side car enterprise. The LS 200 of Steib was an appropriate side car, which requires however a special of the Kardanantriebes. The shields and the tank are like the rims from steel sheet. The front shield trained still the swung dirt rag in the steel sheet with, which is missing with the successors R 26 and R 27.

The engine mount is like the transmission and the rear-axle drive from aluminum casting. BMW R 25/3 had like BMW R 25/2 rubber bushes for the storage of the engine in the housing for two knockout spindles. The silencer is fastened with clips directly to engine axle and framework.


The engine is as outside with the predecessor model BMW R 25/2 a longitudinal a cylinder four stroke engine with lateral cam shaft and beside the grey cast iron cylinder in chromium-plated steel tubes led push rods. These operate the rocker arm in aluminum cylinder head, which operates the hanging valves for its part (OHV). The rocker arms are stored like the connecting rod bearing in bronze sockets. The cam shaft is propelled over a simplex chain from the crankshaft. The oil pump is in the oil pan and is a simple gear pump, which is propelled over a Schneckentrieb (reduction) by the cam shaft.

On the front crankshaft stump the totally enclosed generator sits behind the steel sheet cover. The generator is a direct current generator. The load automatic controller for the Bleiakku sits under the steel sheet cover of the generator.

On the rear crankshaft stump the heavy flywheel (also - in the eyehole observably - ignition adjusting marking) sits, which takes up the a disk drying clutch. The clutch is operated by means of an axial-thrust bearing via a pressing rod, which runs by the hollow transmission main shaft.

The carburetor is a 22er Bing Schwimmerkammervergaser with conical needle in the round slidegate valve. The wet air cleaner element is at the end of a pipe, which runs parallel to the tank soil by the tank and ends in the proximity of the Telegabel. The connection of this long sucking in pipe between tank and carburetor manufactures a rubber connecting piece. The intake filter is a steel net, which is soaked with oil, at which the dust settles. It serves the rough filtering of the intake air. The air cleaner is not changed but is not cleaned for maintenance, and is again moistened with oil.


The drive strand requires a flexible torque transmission element at the transmission exit. In addition still another black rubber four-perforated disk (flexible disk) at the two-finger flange of the transmission is postponed with this model, which transfers the torque of the transmission output wave to the two-finger admission of the cardan shaft. This flexible disk is as equipped with the successors for stability reasons with a circulating chromium-plated steel ring.

The cardan shaft to the rear wheel is high polish-chromium-plated and unsolicited. The universal joint of the cardan shaft fastened to the Winkelgetriebe is covered against dust with a chromium-plated cylindrical fuseholder. Against this cylindrical fuseholder runs a seal rubber rotary with the wave, which keeps the loose dirt away from the universal joint. The Winkelgetriebe in the Alugusskorpus is equipped the quiet running because of with (90"° detour). The of the bellcrank runs in a special heavy transmission oil for high flank pressing

Wheels, brakes

R 25/3 was the first Einzylinder Motorad of BMW, which had aluminum full hub brakes, but still steel wheels. The predecessor model R 25/2 had still steel half hub brakes ("dose covers" - brakes) with steel wheels, which do not reach the delay values like the modern aluminum hubs with larger break area. BMW R 25/3 was the last a cylinder model in the tradition of the Vorkriegs motorcycles BMW R 23, BMW R 24 and R 25.

Building end

R 25/3 in the year 1955 by the model BMW R 26 was replaced, with uprated engine (11 kW/15 HP) and a completely new chassis in. The basic concept of the drive remained the same, however so much changed with R 26 that these and their successor R 27 form another category.

Technical data

  • Four-course foot transmission with zus. Gearshift lever
  • Flexible disk and open cardan shaft to the rear wheel
 R 25
DesignA cylinder with Kardan
EngineFour-cycle OHV
Construction period1947-1948
Drilling (mm)68
Stroke (mm)68
Capacity247 cm
Achievement9 KW/12 HP
Consumption approx. (ltr/100 km)approx. 3
Vmax120 km/h/with side car 90 km/h
Unloaded weight150 kg
Total weight320 kg/450 kg with side cars
Level of fuel in the tank12 ltr

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