BMW R 61

A BMW R 61 built in 1938

BMW R 61 with sidecar

The BMW R 61 is a 1938 to 1941 of BMW produced motorcycle with flat-twin four-stroke engine and shaft drive . As a touring model with a side-controlled engine, it was the sister model of the R 66 , which was designed as a sports model.

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. In 1938, the R 61 replaced the R 6, which was only built in 1937 .

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

technology

engine

The motor M 261/1 was equivalent to previous models, a longitudinally mounted twin-cylinder boxer - four-stroke engine with standing valves.

drive

The R 61 had a foot-shift four-speed gearbox. The entire drive train was encapsulated against dirt and moisture and, apart from the seldom required oil change, was maintenance-free, in contrast to the chain drives that were almost always unencapsulated at the time.

Rear wheel drive

The rear wheel was driven by 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

Technical specifications

Parameter	Data of the R 61
drilling	70 mm
Hub	78 mm
Displacement	600 cc
Compression ratio	6.0: 1
power	18  hp (13  kW ) at 4800 min -1
Top speed	110 - 115 km / h
Empty weight	184 kg
Tank capacity	14 liters

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 .

Web links

Commons : BMW R 61  - collection of pictures, videos and audio files

• BMW R 61. In: BMW History. BMW AG, accessed on December 28, 2015 (dossier of the BMW Group Archives). 

Individual evidence

1. ↑ 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). 
2. ↑ ^{a b c} 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). 
3. ↑ Spare parts list for the BMW R 51, R 66, R 61 and R 71 motorcycles. In: BMW Geschichte. BMW AG, April 1938, accessed on December 29, 2015 (spare parts list with pictures, 87 pages).