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BMW R 60/2
Thirteen years ago a sidecar outfit powered by a BMW flat twin won the FIM World Sidecar Championship. It was not the Bayerishce Motoren Werke's first appearance in championship colors, for the factory's supercharged twins had been strong contenders in prewar racing, winning the senior solo championship in 1938. What was to be important about that 1954 victory was its initiation of an uninterrupted series of class championships which continues to this day. For thirteen years BMW has held the sidecar crown, and for twelve years it has been marketing its "sidecar" production motorcycle, the model R60.
In an era of rapid technological change, one might reasonably ask how any motor company could successfully sell the same model for 12 years, especially when the sidecars that model was meant to haul have virtually disappeared from the world's highways. The reasonable answer to that question is complex, for the idiosyncratic mind of the motorcyclist is not about to lend itself to uncomplicated explanations. But we might begin by looking at this month's test R60 for characteristics that prove useful in a solo.
The sidecar outfit was once a sort of poor man's car. A man could buy an inexpensive (by auto standards) motorcycle, ride it solo until he had saved up enough to add a sidecar, then take the wife and kids along with him. Over-all investment would still be less than for an automobile, and running costs considerably less. Well, mass production changed that idea almost before it got off the ground. "Basic transportation" in an automobile has for some time been cheaper than a good sidecar rig with comparable performance.
Other than power, what the sidecar man needs from his engine is high torque and good but not abrupt engine braking. He prefers a reliable, mildly tuned engine over a peaky, temperamental scorcher. Cooling characteristics have to be very good, for a sidecar rig is heavy, has lower gearing, and gets less cooling air at a given rpm than a solo. Owing to the way a chair corners, the engine needs a pronounced flywheel effect to keep power delivery smooth and to prevent wild overreving during wheel breakWay in power slides. Also important is carburetion that does not lean out under horizontal g-loads in cornering. For best stability as well as minimum wind resistance, the sidecarist prefers an engine with a low height and center of gravity, permitting the outfit to lie close to the ground.
Most of these requirements can be quite useful in a solo bike, depending on one's riding habits. And apparently the R60 suits the riding habits of quite a few for it is the most widely sold BMW in the U.S. A heavy flywheel does contribute to smooth engine output, especially if the firing pulses are even and if the engine's reciprocating masses (pistons, con-rods etc.) are balanced against one another—as they are in the horizontally-opposed R60 powerplant. Low center of gravity helps the handling of any motorcycle. And mild tuning combined with the frame rigidity necessary for a sidecar make for an extraordinary reliable and robust unit.
Most of our readers are already familiar with the basic BMW layout; it has been around in the R60 for 12 years and in other models since 1923, a year after Master engineer Max Friz of Munich conceived it. The horizontally opposed engine, its crank aligned with the fore-and-aft axis of the bike, couples through an engine-speed clutch to an in-unit gearbox at the rear. From the gearbox, a universal joint, shaft, and bevel gears, carry the drive to the rear wheel.
We have known serious motorcyclists in moments of cynicism to remark, "The BMW represents a triumph of development over design." Let us now examine a few developmental details that might inspire such a remark. The BMW is packed with particulars of great ingenuity and high manufacturing skill.
The engine, for example, gets its intake air from two sources. The first is through the centrally mounted air filter, which feeds both carburetors through a common chamber via separate tubes. The second intake is by way of small vents in the nose cover on the engine unit. Under this cover sit the magneto, braker points, capacitor, generator and voltage regulator. Intake air passes over these components, keeps them considerably cooler than crankcase temperature, then passes through a crankcase passage, another air filter, and into the common chamber under the main air filter.
The electrics, made by Bosch of Germany are a bit old-fashioned by present standards, but in the BMW they are far more reliable than the components commonly fitted to other bikes. The 60-watt DC generator puts out an actual 90 watts at any crank-speed over 1700 rpm. The magneto is mounted on the end of the camshaft and turns at half engine speed. The braker cam has two lobes, thus opening the points once per crank revolution. This magneto is completely independent of the generator-battery system. Starting is invariably a one-kick job, and the bike can be driven safely, even at night, with a dead battery. The electrics are also completely water proof—mostly undercover and carefully protected.
Behind the enclosure for the magneto and generator is another cover for timing gears. A large gear mounted on the crank drives a gear for the camshaft and a gear to oil pump. A continuous oil stream plays out of a jet into the meshing of the mainshaft-camshaft gears. These have been individually selected and fit at the factory down to the exact size of each crankcase housing, and there is only .0005 inch of backlash. The mainshaft gear also carries a flat plate with cutaways that precisely time crankcase breathing. The cutaways alternately open and cover vents to the crankcase much like the rotary intake valves on modern two-strokes.
The crankshaft itself is a hefty built-up (or pressed together) unit with large roller bearings at the connecting-rod lower ends. The crank turns in two roller-type mainbearings. The lack of a central main-bearing means some crank flexing at higher rpm, but this does not become a serious problem within the R60's rev limit of 6200 rpm. Seen from above, the cylinders are slightly offset, creating a rocking movement about an axis perpendicular to the plane of the cylinders. Not only is this slight, but it is well damped by the R60's frame. In dynamic terms, the horizontally-opposed flat twin is the best balanced of any of the common motorcycle configurations. In the R60, this is felt as extraordinary smoothness and virtually vibration-free operation throughout the power band. With its 7.5:1 compression ratio and conservative valve timing, the R60 is also very tractable with strong pulling power (torque over 26 ft-lb.) anywhere above 2500 rpm.
Although the solo R60 used the same single-dry-plate clutch as the sidecar unit, it has a gearbox and rear drive with taller ratios. At maximum torque in fourth gear (4200 rpm), the R60 is rolling along at 65 mph, a very smooth and comfortable cruising speed that consumes just a shade under 50 miles per gallon of regular gas. The engine will not quite pull maximum power in fourth gear, which at 6000 rpm and 32 bhp would be 92 mph. Instead, it rises to a steady 5800, or 86 mph, and stays there.
Some nice touches in gearbox construction are hard-chromed shifter-fork tips for longer wear, a clutch throw-out bearing running in transmission oil, and gearbox venting to the atmosphere through a small hole in the speedometer drive. The speedometer drive gear has been designed with an extra return spiral that sends any condensed oil vapor back to the gearbox rather than out the breather hole. Result, a clean gearbox that rarely blows its oil seals. The only disadvantage to this gearbox: its input shaft runs at engine speed. A heavy flywheel keeps that engine from changing speed too quickly and often delivers quite hefty jolts to the input shaft on gear changing. Consequently, a spring-and-cam type torque damper is fitted to the input shaft. This protects the gears from the engine side, though the necessity of running two offset shafts for the gear pairs is less efficient mechanically than the more conventional arrangement of two shafts total.
Protection from wheel-delivered shocks is provided partially by the drive shaft itself, which permits a slight amount of both lengthwise and torsional flex. Normal change of length required by movement of the rear suspension is provided by a sliding splined-cup joint at the rear of the shaft. An elaborate linkage to the rear brake arm also keeps an even braking tension on that arm despite vertical movement on the rear wheel.
Counting the rear drive unit, the R60 has four separate oil enclosures, each of which must be sealed off from the others. There is the crankcase and wet sump, the transmissions. The universal joint and shaft drive, plus the rear drive. Virtually every rotating load-carry surface within this series runs on roller or ball bearings and all receive a generous oil bath. Again, a good case for lengevity. The only possible catch is maintaining all those oil seals.
Every enclosure but the shaft drive housing is adequately vented and part of the latter is a neoprene expansion boot over the universal joint. This offers enough low-resistance expansion volume to obviate positive venting.
The frame through which this power train passes is basically a sidecar frame. That means it's strong and heavy. BMW uses all kinds of tricks in the basic double-loop cradle, such as varying cross sections at different points according to load. Much of the tubing, oval sectioned and tapered, is very expensive to fabricate. Helmut Kern, service manager at Butler and Smith, the U.S. importers of BMW says, "As far as I know this is the only frame that you can hook a sidecar to, and later ride solo. Any other frame I've tried will eventually distort under the loads imposed by the sidecar, throwing it out of alignment for solo work."
Another vestigial sidecar component that benefits the solo rider are the R60's brakes. The sidecars BMW made (but no longer make) had a brake in the wheel, but many machines were fitted by owners with less expensive, brakeless rigs.
This meant that the bike's brakes did all the work, which might be hauling a 1400-1b. package to a standstill from 65 mph. It is not surprising that BMW was the first firm to fit full-width brake hubs on all production motorcycles. They were also among the first to use a double-leading-shoe brake at the front. Twelve years ago these brakes paced the industry and were undoubtedly the best production stoppers available. They are still above average for large-displacement bikes, but technology has caught up with, and in some cases, passed BMW. Our specific brake loading figures show what our riding experience confirms: The R60 has good brakes, but they could be better for such a large machine.
Up front the R60 also features one of the most unique forks in the motorcycle industry. A full Earles-type leading-link fork, it has both advantages and disadvantages compared to the more common telescopic variety. Like so much else on the BMW, the fork is both heavy and strong. It was ball-and-cone bearings at the steering head and taper-rollers at the swingarm pivot. Under heavy braking, the swingarms want to turn forward about the pivot, effectively raising the bike. At the same time momentum transfers most of the weight of the bike and its rider forward, forcing the front end down and swingarms backWard. The effects are self-cancelling, and the BMW brakes very evenly without nosedive or lifting.
The rear swingarm of the BMW also pivots on tapered roller bearings. Its suspension units are the conventional coil-spring and shock-absorber combination, but they are secured at the top in housings welded to the rear of the frame loops. The pivot points are located in two vertical members connecting the lower and upper cradle sections. This arrangement does not offer best resistance to side loads at the wheel and we experienced what felt like flexing during hard cornering with two up.
Our test of the R60 was rather more thorough than most road tests, for not only did we run it at the track, we also drove it 1400 miles from New York to Daytona. BMW has produced some 250,000 motorcycles since World War II, and they gave us our test bike to celebrate the fact. It was completely stock, we drove it hard, and we experienced no mechanical difficulties. There was some sweating at the vertical crankcase joints, but no .oil leakage and virtually no oil consumption.
The R60 is most at home on the open highway, where it will cruise smoothly at 65 or 70 for day after day almost without end. It is a big machine, almost overdesigned and certainly overbuilt for a solo mount. Such a "utility" orientation makes the R60, not surprisingly, the largest selling police motorcycle in the world. But utility demands good manners, strength, and durability. The R60 exhaust note is low and mellow, emerging from an interconnected twin-pipe, twin muffler system. Workmanship, fitting, finishing —all are superb. Buyers have an option of various seats, tanks, handlebars and racks. Ours had the solo seat, which is quite comfortable, but far too low for the high "touring" bars fitted.
The R60 is certainly no road sports machine. It will do zero to 60 in a shade over 16 seconds, and third gear will carry you to about 78 mph for brisk passing. But the combination of 440 lbs., 30 bhp, and a heavy flywheel doesn't make for neck-snapping acceleration, or ear-holing at high speed through a series of left and right hand switchbacks. That heavy front end and over-all weight just can't be thrown back and forth quick enough for hard tight-course riding. This is a machine for long distances, for a comfortable, trouble-free ride, for the rider who wants more to see the country he's passing through than to explore the limits of his cornering and braking skill.
Routine servicing of the BMW is easy. All the oil reservoirs are readily tapped, the electrics can be reached by undoing two bolts, and the valve gear, pistons, cylinders and carburetors hang right out there for ready service and adjustment. Naturally, there is no "greasy chain" to fuss with. In contrast, power-train servicing is a nightmare. Lower end, transmission, drive shaft, and rear drive overhauls require more special pullers, drifts, jigs, wrenches, holders, and fixtures than one can imagine, much less afford. And breaking the power train to service it is a lengthy, exasperating job. Fortunately, for BMW owners, the R60 is built to last, and we know one chap who has 270,000 miles on his bike without ever having so much as removed a cylinder head.
Ironically, as history's clock has caught up with and passed BMW, there has been a recent resurgence of interest in sidecars. The R60 may once again serve for a limited few its original task. Butler and Smith now markets Dutch-made single-passenger sidecars under the BMW marque. Meanwhile, the factory has been blossoming financially under the demand for its automobiles and is completing a new facility for motorcycle manufacture. Although now said to the point of weariness, the near future may bring new models and more modern designs from BMW. Meanwhile, the R60 will continue to do its workhorse chores with the characteristic stamina and unfaltering good manners, that have made it a favorite of long-distance touring riders.
Source Cycle Magazine