BMW R 27
The model R 27 is a 1960 to 1966 of BMW produced motorcycle with single-cylinder four-stroke engine and the last model of the single-cylinder BMWs with shaft drive .
With this model, the era of German motorcycle construction ended, when a motorcycle was still the main means of transportation. The emerging competition between inexpensive cars on the one hand and sporty Japanese motorcycles for leisure time on the other led to the end of the market for this type of elaborately built motorcycles in what was then the Federal Republic of Germany - unlike in the GDR. Their special properties made the BMWs, like the R 27, excellent touring machines that could be used to cover long distances without getting tired.
See also the article on the full swing BMW .
previous version
The predecessor of the R 27 was the BMW R 26 with 11 kW (15 hp), cardan shaft drive and essentially the same frame with front and rear swing arm . The R 27 differs from the R 26 in that it has a four-stroke engine that was boosted to 13 kW (18 hp) and was no longer connected to the frame with quick-release axles, but instead was placed on elastic rubber buffers ("floating motor").
Design features
The frame is welded from tubular steel and is suitable for sidecar use due to its great stability. In terms of its design, it is almost equivalent to that of the much faster two-cylinder BMW, but it has oval - instead of circular - down tubes.
The R 27 never had laterally attached ball heads for sidecar operation as standard. A special subframe was always required. The Steib S 250 sidecar is a suitable sidecar model. Sidecar operation requires a special gear ratio for the cardan drive, which could be ordered from BMW: With a shorter ratio, the maximum speed is reduced, but the tractive effort increases.
The mudguards and the tank are made of sheet steel, rims and hubs are made of aluminum . The engine block, like the cylinder heads and the gearbox and rear axle drive housings, is made of cast aluminum . While the previous models, the BMW R 25/3 and the BMW R 26, only had rubber bushings to mount the engine in the housing for two quick-release axles, the drive suspension of the R 27 is more elaborate: the engine and gearbox each stand on two rubber-metal elements ( Elastomer bearings ). The engine has a fifth stop on the cylinder head with another rubber-metal element. This means that the motor-gearbox unit is completely covered in rubber. The muffler is also elastically mounted to keep vibrations from the frame. Mechanical noises and vibrations from the engine and transmission are not transmitted to the chassis and the driver. This made the R 27 an extremely quiet and low-vibration type of motorcycle for the time. This low-vibration property makes all BMWs popular travel machines based on this design principle.
engine
As in the previous models BMW R 25/3 and BMW R 26, the engine is a longitudinally installed single-cylinder four-stroke engine with a half-height camshaft on the sides and bumpers running in chrome-plated tubes next to the cast iron cylinder . These actuate the rocker arms in the cylinder head , which in turn control the hanging inlet and outlet valves ( OHV engine ). Like the piston pin, the rocker arms are mounted in bronze bushings, the crankshaft in ball bearings , and the connecting rod in a roller bearing. The camshaft is driven by the crankshaft via a simplex chain running in an oil bath. The oil pump, a simple gear pump , is located in the oil pan. It is driven by the camshaft via a worm drive ( reduction ).
The largely watertight alternator sits on the front crankshaft stub behind the aluminum cover. BMW had outsourced the centrifugal governor and the ignition switch to the camshaft on the R 27 . The charge regulator of the 6-volt direct current generator is located under the tank, the 6-volt lead-acid battery behind a cover on the left-hand side.
The heavy flywheel is located on the rear stump of the crankshaft and shows the ignition timing markings in the inspection hole. The flywheel takes on the single-disc dry clutch . The clutch is operated with a thrust bearing via a push rod that runs through the hollow main shaft of the transmission.
The carburetor is a 26 mm Bing slide carburetor with a float chamber and a round slide with a conical nozzle needle. The air filter element is located on the right side cover. The first machines (up to serial number 379580) used the same washable, oil-soaked wet air filter as the R 26, then a dry air filter element that can be cleaned with compressed air, but has to be replaced later.
Due to the enlarged cooling fins of the cylinder and the cylinder head, the cooling problems that were sometimes observed with the predecessors in sidecar operation no longer occurred.
drive
Like the previous models, the R 27 has a foot-shifted four-speed gearbox with dog clutch, neutral indicator and kick starter . An additional manual gearshift lever often found on earlier BMW motorcycles had already been omitted on the R 25/3. The drive train requires an angularly movable and displaceable joint at the transmission output because of the movable rocker. For this purpose, a disk made of an elastomer with four holes ( Hardy disk ) is pushed onto the two-finger flange of the gearbox, which transfers the torque from the gearbox output shaft to the pins on the flange of the cardan shaft. An aluminum cap, which is attached to the gearbox, encloses the Hardy disc. The cardan shaft to the rear wheel runs dry in the steel tube of the rear wheel swing arm, which at the end accommodates the aluminum housing of the bevel gear with bevel gear pair for 90 ° deflection.
The entire drive train is encapsulated against dirt and moisture and maintenance-free apart from the rarely required oil change, in contrast to the chain drives that were almost always unencapsulated at the time.
landing gear
The chassis is a welded double tubular steel frame . Except for the modified engine mounting, it corresponds to that of the BMW R 26. On the front wheel, a pushed long-arm swing arm with two spring struts and oil pressure shock absorbers is used to guide the wheel. The rear wheel is guided on a long swing arm, also sprung and dampened on two spring struts with integrated oil pressure shock absorbers. The rear spring preload can be converted to operation with a passenger in two stages. The chassis proved to be on a par with the competing models of the time until the end of construction. A special feature is the attention to detail prepared sidecar operating possibility: The front long rocker can with a repluggable threaded rod for ease of maneuverability in the team operating on short lag to be changed. Two additional bolt eyes under the steering head allow a different position of the front shock absorbers, which can be used for greater ground clearance .
This type of front wheel guidance has not been surpassed for sidecar use to this day, over fifty years after its appearance. Modifications of modern, much more powerful motorcycles for sidecar operation also have long swing arms.
On the other hand, when it comes to operating as a solo motorcycle, the front long swing arm has always been criticized for moving large masses around the steering axis, which results in reduced maneuverability. The successors of the large models had a telescopic fork instead of the front swing arm - and the export models of the "full swing BMW" for the USA had a telescopic fork since 1965, at the same time as the end of the R 27 then the successor models equipped for all markets. For this reason, BMW no longer released these models (the USA machines from 1965 and the “/ 5 Series” series from 1969) for sidecar operation.
End of construction
The BMW R 27 was produced at a difficult time for the German motorcycle industry. The motorcycle manufacturers sought their salvation in other products or in the production of machines up to 50 cm³. At the same time, often underestimated at first, Japanese manufacturers, especially Honda , pushed their way onto the German market . This led to a reorientation of the market. The motorcycle developed from a mere means of transport to a hobby vehicle that was operated in addition to car ownership. As of January 1, 1965, around 29,000 motorcycles were still registered in the Federal Republic of Germany, of which around five percent were from Honda. At that time, the R 27 with the Honda CB 250 and Yamaha YDS-2 with 22 HP (16 kW) and 24 HP (18 kW) were faced with more powerful motorcycles with a sporty image. The R 27 suffered from the high manufacturing costs that were not significantly lower than those of the two-cylinder boxer engines.
There was therefore no successor for the R 27 at BMW in the class up to 250 cm³. A planned renewal called the R 28 (with telescopic fork of the later BMW / 5 series) was stopped before the market launch and the R 27 continued to be built for about three years until the / 5 series of the two-cylinder appeared and BMW full swing motorcycles disappeared from the market.
A total of 15,364 units were manufactured from 1960 to 1966 (serial numbers 372001–387364).
The official last sales price in 1966 was DM 2,670.
BMW as a government motorcycle
The R 27 model was also procured for the Bundeswehr in standard Bundeswehr paintwork , for the German Red Cross in ivory paintwork and for the police authorities in police green ( RAL 6009 fir green) and was mostly used for training purposes. Tens of thousands of soldiers in the 1960s and 1970s learned to ride a motorcycle on BMW R 26 and R 27.
Others
The ambivalence of BMW at that time and the search for marketable vehicle solutions can also be seen in the use of this same single-cylinder engine type in the BMW Isetta small car . In the Isetta, the engine is only supplemented by fan air cooling and a starter generator ("Dynastart"), which means that the alternator and electric starter are combined in one machine. Power-hungry single-cylinder motorcycle owners used engine components from the 300 Isetta (crankshaft, pistons and cylinders) to give their R 26 and R 27 a little more displacement and power. Even entire Isetta engines, including fan cooling and electric starters, found their way into the motorcycle frame in isolated cases: possibilities of the modular principle and ambitious tinkering. Anyone who rode a motorcycle at that time usually did all repairs and maintenance work themselves.
The BMW R 27 was the last BMW single-cylinder model before it was released, the enduro BMW F 650 designed jointly by BMW and Aprilia and manufactured in Italy . It was built in the 1960s and thus in the great downturn in the German motorcycle market.
Technical data of the R 27
- Full swing frame with suspension of the motor-gear unit in elastomer bearings
| design type | Single cylinder with cardan |
| engine | Four-stroke OHV |
| transmission | Four-speed footshift |
| construction time | 1960-1966 |
| number of pieces | 15,364 |
| Bore (mm) | 68 |
| Stroke (mm) | 68 |
| Displacement (cm³) | 247 |
| Power (kW / PS) | 13/18 at 7400 rpm |
| Consumption approx. (L / 100 km) | 3.9 |
| V max (km / h) | 130 / with sidecar 90 |
| Empty weight kg) | 162 |
| Total weight (kg) | 325 / with sidecar 480 |
| Tank capacity (l) | 15th |
literature
- Helmut Krackowizer : Schrader Motor-Chronik, vol. 11, BMW motorcycles single cylinder R 24 to R 27 1949-67 , Motorbuch Verlag, 1999
- Tragatsch: All Motorcycles , ISBN 3-87943-410-7
- Motorcycle Classic 3/88
- Hans-Joachim Mai, 1000 tricks for fast BMWs, 11th edition 1988, Motorbuch-Verlag, Stuttgart
- Ernst Leverkus , The great motorcycles of the 1960s
Web links
- BMW R 27. In: BMW History. BMW AG, accessed on August 25, 2017 (dossier of the BMW Group archive).
- Handbook motorcycle R 27. (PDF) In: BMW history. BMW AG, August 1960, accessed on August 25, 2017 (manual with pictures, 46 pages).
- R27 at the police
- BMW single cylinder center
Individual evidence
- ↑ Price list motorcycles. In: BMW history. BMW AG, July 1966, accessed on January 17, 2019 (document in the BMW Group Archive).
