Full swing BMW
The era of the so-called Full Swing BMW began in 1955, as so-called frame full swing in the German motorcycle moved in, and ended in 1969 with the BMW R 69 S . The new design of the chassis for the model year 1955 by BMW had a pushed front wheel long swing arm with friction steering damper and adjustable caster for trailer operation as well as a rear wheel swing arm with a completely encapsulated cardan shaft running in the right swing arm in the oil bath (see picture for this on BMW R 50 ); the preload of the rear suspension can - at that time new at BMW - be adjusted without tools. This BMW design appeared in 1955/1956 for the large two-cylinder with 500 cm³ and 600 cm³ and for the single cylinder with 250 cm³ displacement. In the top models R 50 S and R 69 S released in 1960, the friction damping was replaced by a hydraulic steering damper.
construction
The front and rear swing arms on the BMW models are each provided with two tapered roller bearings , which can absorb both the side and the axial pressures that occur - especially when driving with a sidecar. The tapered roller bearings are kept at a distance on the quick-release axle with spacer tubes. The bearing shell halves sit in the swing arm and the tapered roller cages are located on the quick-release axle. A shaft seal in front of the tapered roller bearings protects the bearings from the ingress of dirt and moisture. While older swing arm models always had a quick-release axle both front and rear, modern rear swing arms only have one threaded bolt each on the right and left, which is tightened with a two-hole wrench or an Allen key. The countering also happens here with a mother. The protruding threaded stump is given an aluminum cap to protect it against dirt and moisture .
Adjusting a long arm swing arm correctly requires skill. After tightening the swing arm bearings, the quick-release axle must be locked with a nut. A rocker arm is considered to be properly adjusted (not too tight) if it can be easily moved up and down without the shock absorber.
history
In the early 1950s, instead of new developments, old models continued to be produced almost unchanged for some time in German industry in order to be able to meet buyers' needs more quickly. With a redesign of the two-cylinder engine and an increase in performance of the 600 engine in the BMW R 68 to 35 hp, however, it had become clear even before the mid-1950s that the chassis of these BMW types was inferior to English competitors from Triumph , BSA and Norton also mostly had lower prices: The old BMW chassis design with front telescopic fork and above all the straight travel suspension on the rear wheel with very small spring travel and poor damping was sharply criticized. With the sporty 600 model "R 68" in particular, BMW exposed itself to the unavoidable criticism of having installed an engine that was now clearly too fast in a "too slow" chassis. This combination overwhelmed many drivers; Due to the chassis weaknesses - and the lack of experience of some drivers - there were many accidents with these machines.
After this criticism, BMW constructed a completely new double-loop tubular frame including swing arm guides for the front and rear wheels (analogous to the “spring bed” frame of the English competitor Norton ). In 1955 and 1956 the following new models appeared with this frame construction:
- As the successor to the successful 250cc single-cylinder model R 25/3 , the R 26 came out in January 1956 with a power-boosted engine from 13 to 15 HP (11 kW),
- the two-cylinder model R 51/3 was replaced by the R 50 with an increase in output from 24 to 26 hp
- as the 600 successor to the R 67/2 , the R 60 came out in 1956 with an unchanged engine with 28 hp and
- In 1956 a "sports model" with the 35 hp engine of the R 68 appeared under the designation R 69.
With the presentation of the full swing street models in 1955 - in the series racing model "RS 54" this chassis had been on sale since 1954 - the R 67/2 was slightly revised and delivered ex works (only) as a team under the designation R 67/3 ; until it was replaced by the R 60 in 1956, 700 copies were made.
At that time, the combination of a powerful engine and a stable swing-arm chassis could only be beaten by a few equally powerful English motorcycles, but at the expense of comfort: the BMW chassis was popular with experts when it appeared highly praised. The double-loop tubular frame benefits from oval-drawn tubes, the load-related profile alignment of which has a higher bending moment of resistance than conventional round tubes with the same weight .
In the USA, where over 80% of the two-cylinder engines went, John Penton drove a BMW R 69 from New York to Los Angeles in record time , in 53 hours and 11 minutes. The previous record holder took 77 hours and 53 minutes on a 750 Harley-Davidson .
Five years after the introduction of the swing arm models, there was a small facelift. The R 27 model was introduced with a single-cylinder engine, which with 18 HP was characterized by three additional HP and now also by an elastic and vibration-damping suspension of the motor-gear unit. In the two-cylinder engines, the frame was reinforced in a few places; the model names changed for the touring models to R 50/2 and R 60/2 .
The model R 69 experienced when revising a serious increase in output of 35 to 42 hp, and received the type designation R 69 S . However, the increase in output soon led to difficulties: As a result of the retained roller bearings on the crankshaft, the increased mean pressures and higher speeds of the sports engine, vibration problems increased, which in some cases led to the crankshaft breaking under full load, including a cylinder torn off, broken engine housing and total engine damage . BMW responded and a short time later became the first series manufacturer to install a vibration damper under a modified front housing cover on the end of the crankshaft opposite the clutch. This vibration damper required an adjustment of the front wheel swing arm: the lower pipe bend for the mudguard was flattened to allow the fork to swing through. At the same time, a 500 "sports model" was also introduced, the extremely rare R 50 S , only 1634 units made until 1962 , which is the same as the R 69 S except for the smaller displacement and does not have a crankshaft vibration damper.
However, all these measures could not prevent BMW's sales from falling further during the German motorcycle crisis, because the affluent public wanted to drive a car and a new VW Beetle was not much more expensive than one of the elaborately and high-quality manufactured heavy BMW motorcycles. In 1965, the swingarm BMW intended for export to the USA had a facelift . In the United States, motorcycling was already beginning to establish itself as a leisure activity and hobby. For export, BMW replaced the heavy front swing arm with a lighter telescopic fork, which BMW then used in series production of the same type in the successor models of the so-called " Stroke Five Series" from 1969. Optionally there was now also an electrical system with twelve volts DC voltage.
After the introduction of the new models in 1969 with up to 50 hp, many of the old “cast iron” motorcyclists mourned the swingarm models, cherished and looked after their older “sweethearts” and supplied themselves with inexpensive parts-carrier machines to prevent the vicissitudes of aging motorcycles. In the event of engine damage, BMW also approved the newer engines with the same connection dimensions, now with plain bearings, for installation in the full swing frame. Initially, the performance limit for this was the 50 hp of the new R 75/5 , but later, with a different front brake system, even more powerful motors were approved for installation in the swing arm frame, often without driving in a trailer and using the newer telescopic fork. The modular system from BMW made these conversions technically largely unproblematic.
Purchase and restoration
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The modular concept made it possible to restore the machines long after the end of production at a reasonable cost. The top models from 1960 onwards are extremely expensive; for an original R 69 S with "matching numbers" (matching frame and engine numbers), up to 20,000 euros are required when new. Many machines have been rebuilt and equipped with different engines. Original machines are therefore rare.
Some dealers, preferably in southern Germany, specialize in full swing BMWs and deal in machines, spare parts and accessories. You are buying up leftover stocks from international police and government fleets; French police held thousands of swing-arm BMWs. Smaller fleets have gone to South Africa and South America and are now "brought home" in containers . You can occasionally recognize the authorities' machines by their tank fittings for the radio; there is then a lack of a capacity of approx. three liters on the tank content. Instead, there is an additional tool compartment flap on top , under which a radio used to be located.
Today's perception
Today, the BMW motorcycles of the full swing era have become coveted vintage motorcycles. Conversions are no longer sought by their owners, they usually pay attention to originality - apart from the double- sized Hoske tank with Harro tank bag of the mostly black painted " rubber cows ".
All of these things belong to a time that older BMW drivers only rave about when they hear the words “full swing BMW”.
The joy of the full swing BMWs had already become an exclusive joy in the last few years. Most motorcycle fans had become car customers during the years of decline of the West German motorcycle industry. Only a small group of people continued to enjoy sporty motorcycling, who - if they drove BMW - called themselves "Die Gusseisernen". Your best-known exponent was Ernst Leverkus , long-time editor of the magazine "Das Motorrad".
Historical consideration
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Long before all-wheel drive cars were introduced, heavy motorcycle combinations were the best way to be mobile in winter . Once the team driver got used to the asymmetry of the driving characteristics, there was no faster and safer means of transport on ice and snow than a large team at that time - however, the famous Wehrmacht teams with reverse gear and selectable side wheel drive were no longer in production. The BMW two-cylinder of the 1950s and 1960s - after Zündapp discontinued production of the " KS 601 " model in 1957 - were the culmination of series motorcycle production for sidecar purposes; Moto Guzzi sidecar motorcycles did not appear until the later 1960s. With all of the successor models, BMW decided not to approve the motorcycles for use in a sidecar as standard; because solo frames are easier and cheaper to manufacture.
At first, the era of the motorcycle as a means of transport for the “little people” was coming to an almost imperceptible end. The trend among buyers of individual mobility was towards vehicles with a “roof over their head” and thus away from the motorcycle. The function of a motorcycle as part of leisure activities was only a side effect at that time. A motorsport competition with the full swing BMWs was of secondary importance; it was about solidity, reliability and high quality workmanship. The BMW motorcycles, which were already of high quality in terms of workmanship, had become even more stable and massive. Again, they were optionally equipped for trailer operation, mostly with standard four-point attachments for the sidecars , which - depending on their cubic capacity and weight - could be ordered from the Steib catalog or retrofitted. The trailer driver was able to order a suitable secondary ratio for this : the axle ratios of the cardan drive are approx. 20% "shorter" for the weight-disadvantageous sidecar operation. The top speed drops in combination operation, traction and acceleration suffer less.
See also
literature
- Hans-Joachim Mai: 1000 tricks for fast BMWs. BMW two-cylinder motorcycles with no secrets. Stuttgart: Motorbuch-Verlag, several editions from 1971. [9. Edition 1983. ISBN 3-87943-226-0 ]
Web links
- Full swing frame, full swing chassis. In: BMW history. BMW AG, January 1955, accessed on June 6, 2014 (search in the BMW Group Archives).
- BMW full swing motorcycles on the website of an American enthusiast ( Memento from February 26, 2008 in the Internet Archive ) (English)