BMW R 39

BMW
BMW R 39
R39
Manufacturer:	BMW
Construction time:	1925-1928
Number of pieces:
Previous model:	none
Successor:	none
Technical specifications
Engine :	1-cylinder Otto 4-stroke engine
Displacement :	247 cc
Performance :	4.8 kW at 4000 min -1
Gearbox :	Manual transmission
Drive :	Shaft drive
Empty weight :	110 kg
Top speed :	90 km / h
Brakes :	Drum brakes
Tank capacity :	10 l
Fuel consumption :

The R 39 model, released in 1925, was the first single-cylinder motorcycle from BMW , designed as a sporty machine with an engine with overhead valves (OHV design).

history

development

In 1924 BMW developed the R 39 for the 250 cc class. On the occasion of the German Motor Show in Berlin in December 1924, the motorcycle manufacturer presented the company's first single-cylinder model.

Sporting successes

Josef Stelzer won the German road championship of the DMV in the 250 cm³ class on an R 39 in the first year of production in 1925 .

marketing

The design of the R 39 did not differ significantly from the large two-cylinder R 37 presented at the same time . This caused a cost problem, which is why only 855 units could be produced at a price of 1870  Reichsmarks . Production was stopped in 1927; the construction with a pressed-in cylinder liner and a relatively high-lying camshaft was not pursued any further. It was not until 1931 that BMW started building the R 2, a completely new single-cylinder.

technology

The motorcycle appeared in the then common BMW design, with a tubular steel frame and the drawn short oscillating fork for guiding the front wheel.

engine

Engine of the BMW R 39

The engine with overhead valves developed 6.5  HP (4.8  kW ) at 4000 min ⁻¹ .

construction

The motor housing could be divided horizontally. An intermediate gear to the left above the crankshaft drove the camshaft, which was one level higher, the rear end of which in turn drove the ignition system behind the cylinder. The aluminum cylinder with a pressed-in steel liner was cast onto the engine housing.

The camshaft opened the valves via short tappets , bumpers and rocker arms mounted on roller bearings . The cylinder head largely corresponded to that of the R 37 ; the lubrication was ensured through the ventilation of the crankcase.

drive

The R 39 had a manual gearbox with a drive shaft on the right side of the unsprung rear wheel. BMW referred to the power transmission from the gearbox to the rear wheel as a " cardan drive ", the drive shaft as a " cardan shaft " and the gearbox on the rear wheel as a "cardan housing" - technically correct it was only a shaft drive of the rear wheel, as there were no cardan joints. The horizontally divisible gearbox housing was flanged directly to the motor housing. The three-speed input shaft was driven directly by the single-plate dry clutch in the crankshaft's flywheel. The output shaft drove the drive shaft via a hardy disk in direct extension. The kick starter was actuated at right angles to the vehicle's longitudinal axis. The bevel gear housing of the rear-wheel drive was lighter and smaller than that of the two-cylinder motorcycles.

landing gear

The chassis was a tubular frame without rear suspension, the front fork was a drawn short swing arm with leaf suspension. The rear brake was designed for the first time at BMW as a so-called "cardan brake", which acted on the outer ring of the hardy disc.

Technical specifications

Parameters	Data of the R 39
drilling	68 mm
Hub	68 mm
Displacement	247 cc
power	6.5  hp (4.8  kW ) at 4000 min -1
Top speed	90 km / h
Empty weight	110 kg
Tank capacity	10 l

See also

• List of BMW motorcycles

literature

• Erwin Tragatsch: All Motorcycles 1894–1981 . Motorbuch Verlag, Stuttgart 1997, ISBN 3-87943-410-7 .
• Udo Stünkel: BMW motorcycles typology: All series models from 1923 . Delius Klasing, Bielefeld 2008, ISBN 978-3-7688-2451-4 .

Web links

Commons : BMW R 39  - collection of pictures, videos and audio files

• BMW R 39. In: BMW History. BMW AG, accessed on December 10, 2015 (dossier from the BMW Group Archives). 

Individual evidence

1. ↑ ^{a b} BMW presents the R 39, the first single-cylinder model from the BMW brand. In: BMW history. BMW AG, December 10, 1924, retrieved on December 11, 2015 (text in the BMW Group Archive): "At the German Motor Show in Berlin (December 10-18, 1924), BMW is presenting the R 39, the first single-cylinder model."  
2. ↑ Price list No. 28 for BMW motorcycles R 32, R 39, R 37 and the sidecar S 38. In: BMW history. BMW AG, 1925, accessed on December 10, 2015 (document in the BMW Group archive): "BMW single-cylinder model 0.9 / 6 PS"  
3. ↑ BMW R 39 engine. In: BMW history. BMW AG, 1925, accessed on December 11, 2015 (photo in the BMW Group Archive).  
4. ↑ ^{a b c} B.MW single-cylinder motorcycle Type R 39 Appendix to the BMW manual. In: BMW history. BMW AG, 1925, accessed on December 11, 2015 (manual with pictures, 7 pages).  
5. ↑ ^{a b} Spare parts list and tables for the BMW single-cylinder motorcycle Type R 39. In: BMW History. BMW AG, 1925, accessed on December 10, 2015 (spare parts list with pictures, 49 pages).  
6. ↑ BMW R 39: Drawing for type certificate. In: BMW history. BMW AG, July 31, 1924, accessed on December 11, 2015 (drawing in the BMW Group Archive).  
7. ↑ BMW R 39 cardan brake. In: BMW history. BMW AG, 1985, accessed on December 10, 2015 (detailed photo of the cardan brake).