BMW R 71

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BMW
BMW R 71 from 1938
R 71
Manufacturer:	BMW
Construction time:	from 1938
Number of pieces:
Previous model:	none
Successor:	none
Technical specifications
Engine :	Two-cylinder boxer four-stroke
Displacement :	746 cc
Performance :	16 kW at 4600 rpm
Gearbox :	Four-speed
Drive :	Cardan drive
Empty weight :	187 kg
Top speed :	120-125 km / h
Brakes :	Drum brakes
Tank capacity :	14 l
Fuel consumption :

The BMW R 71 was 1938 to 1941, the last motorcycle with seitengesteuertem engine of 750 cc class of the German motorcycle manufacturer BMW .

history

At the motor show in Berlin on February 18, 1938, BMW presented the R 51 , R 61 , R 66 and R 71 models , a new series of large-volume motorcycles with rear suspension.

development

BMW had implemented four engine variants in one chassis - R 51 , R 61 , R 66 and R 71 - and thus created four motorcycles in different classes from 500 to 750 cm³.

"The similarity of the engines, such as the use of the same, all-wheel suspension chassis for all four machines, made it necessary to summarize them in just one manual, which at the same time gives an interesting overview of the entire BMW range in the large class."

- Manual for the BMW motorcycles R 51, R 66, R 61 and R 71

Only a sporty 750 as the successor to the R 17 was no longer in the program.

marketing

In advertising, BMW highlighted the R 71 as a “long-distance touring and sidecar machine with rear suspension for the heaviest loads”. The price of the motorcycle was 1595 Reichsmarks in 1938. Production ended in 1941 after 3458 units - the next civilian 750 cm³ BMW was the BMW R 75/5 in 1969 .

technology

engine

The engines were longitudinally mounted twin-cylinder boxer - four-stroke engine with side valves .

construction

The engine housing was designed as a tunnel housing with an axially installed crankshaft. The camshaft was located above the crankshaft and was driven directly from the front crankshaft stub via a pair of helically toothed spur gears. The camshaft opened the valves via short slide tappets.

cylinder

The cast iron cylinders had removable cylinder heads made of light metal and radial cooling fins. The low compression of 5.5: 1 made the R 71 suitable for "commercial gasoline" - the sister models required a "gasoline / benzene mixture (Aral, Dynamin, Esso, Olexin, etc.)" with higher compressions.

Carburetor

The two Graetzin G 24 carburettors had a common air filter on the gearbox.

ignition

The battery ignition from Bosch worked with an interrupter, which was installed on the front of the camshaft under the protective hood, together with the ignition coil and distributor. The DC alternator with 6 volts and 75 watts of power was located above the motor housing. More powerful alternators were available for government and military customers. The ignition point had to be adjusted depending on the load and engine speed with a lever on the left half of the handlebar.

drive

transmission

The R 71 had a foot-shifted four-speed gearbox with a cardan shaft on the right side of the sprung rear wheel. In addition, there was a hand lever on the right side of the gearbox, which was particularly recommended for quickly finding idle. The tunnel gearbox was flanged directly to the motor housing. The input shaft was driven directly via the single-disc dry clutch in the crankshaft's flywheel.

Rear wheel drive

The rear wheel had a cardan drive with the following elements in the power flow:

• Hardy washer on the output shaft of the gearbox to compensate the angle between the output shaft and the following cardan shaft
• Unencapsulated cardan shaft with universal joint fork on the output side - the visible part of the cardan drive
• Encapsulated universal joint on needle bearings for angle compensation between the cardan shaft and the following wheel drive
• Slidable universal joint fork for length compensation on the input shaft of the bevel gear axle drive
• Input shaft with pinion for driving the crown wheel in the drive housing - power deflection by 90 °
• Needle-bearing driving flange in the drive housing with splines for driving the rear wheel

Frame and chassis

The R 71 had a welded double loop frame with straight travel suspension on the rear wheel. The front wheel was guided by an oil-hydraulically damped telescopic fork . Front wheel, rear wheel and possibly sidecar wheel had quick release axles and were interchangeable.

See also

• List of BMW motorcycles

literature

• Udo Stünkel: BMW motorcycles typology: All series models from 1923 . Delius Klasing, Bielefeld 2008, ISBN 978-3-7688-2451-4 .
• The 2 cylinder BMW R 71 . "MOTOR CYCLING", the well-known English trade magazine, wrote on October 12, 1938. In: BMW (Ed.): BMW Blätter . No. 34 . Munich February 1939, p. 7–8 ( online [accessed on May 8, 2016] in-house communications from Bayerische Motoren-Werke AG).

Web links

Commons : BMW R 71  - collection of pictures, videos and audio files

• BMW R 71. In: BMW History. BMW AG, accessed on July 9, 2018 (dossier of the BMW Group Archives). 

Individual evidence

1. ↑ ^{a b} BMW R 71. In: BMW history. BMW AG, accessed on December 5, 2015 (dossier of the BMW Group Archives). 
2. ↑ BMW presents the model series R 51 / R 61 / R 66 / R 71. In: BMW history. BMW AG, February 18, 1938, accessed on December 29, 2015 (document in the BMW Group Archive). 
3. ↑ ^{a b c d e} manual for the BMW motorcycles R 51, R 66, R 61 and R 71. In: BMW history. BMW AG, April 1938, accessed on December 28, 2015 (manual with pictures, 48 ​​pages). 
4. ↑ BMW motorcycles ahead in technology and performance: R 20, R 35, R 61, R 71, R 51, R 66. In: BMW history. BMW AG, January 1938, accessed on July 9, 2018 (document in the BMW Group Archive). 
5. ↑ ^{a b c d} Spare parts list for the BMW R 51, R 66, R 61 and R 71 motorcycles. In: BMW History. BMW AG, April 1938, accessed on December 29, 2015 (spare parts list with pictures, 87 pages).