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Drawing: BMW

The technology of the new BMW K 1200 S engine

Lateral thinker

It is surprising that BMW installed the engine of the new K transversely according to the current pattern. But in addition to the unusual layout, there are also refined details inside ?? Formula 1 and automotive engineering send their regards.

Boxer or in-line engines, all BMW multi-cylinders of the past had one thing in common: the Bavarian crank-

waves always rotated lengthways. This is also the case in the first, horizontally installed four-cylinder from Munich, the K 100 RS from the
Year 1984. It has served as a drive to this day in countless variants from the futuristic K1 to the K-75 three-cylinder to the K 1200 LT travel sofa.
But with the K 1200 S now comes the turning point, the crank mechanism of the new four-cylinder turns ?? actually quite conventional? across the direction of travel. Nevertheless, on closer inspection, there is an element of the classic BMW philosophy in it, namely the effort to position the center of gravity as low as possible. This applies to the entire motorcycle and starts with individual components such as the engine. However, you couldn’t lay the four-cylinder completely flat, as it used to be. Then the motorcycle would be too long and the entire periphery would be rather unfavorable. The BMW engineers working with project manager Wolfgang Nehse found the compromise in a cylinder bank tilted by 55 degrees. Which results in an unusual engine layout that, with its many tricks and refinements in detail, is worth a closer look.
They start right at the top of the cylinder head. To tooth chain drives the exhaust camshaft, which in turn is coupled to the intake camshaft by a pair of gears between cylinders three and four. Unlike usual, the camshafts rotate in opposite directions. In addition to a rigid connection between the two shafts, this has the advantage that the inertial forces partly cancel each other out. Another advantage: The chain wrapping around the chain wheel is greater than with a conventional drive. In addition, the chain drive is less stressed because the actuating forces of the two camshafts counterbalance each other to a greater extent.
The inlet camshaft also drives the water pump mounted on the left-hand side, which draws the coolant
transported directly to the hot outlet zones. Attachment to the cylinder head reduces the number and length of the hoses required. Striking: the small and short water jacket on the cylinder block. According to BMW, this significantly reduces the warm-up phase, which improves the exhaust gas behavior and lubrication without this
the engine overheats at maximum power. 73 percent of the volume
flow through the head, only 27 percent wash around the cylinder.
If the four valves with the usual disc diameters (inlet 32, outlet 27.5 millimeters) and a stroke of 9.7 millimeters are still considered the standard configuration, those interested in technology will listen carefully to the valve control. Not the usual bucket tappets, but rocker arms operate the 16 valves arranged at an angle of 21 degrees (inlet ten, outlet eleven degrees). That doesn’t sound very progressive at first because Honda was preparing
Already in 1965 the CB 450 two-cylinder with it, Kawasaki or Suzuki relied on this technology for the GPZ and GSX-R four-cylinder in the mid-80s. Today rocker arms are very rarely found, for example in Husqvarna cross engines.
How modern this technology actually is demonstrated by its use in all current Formula 1 engines. BMW engine designer Wolfgang Nehse sums up the advantages: lower oscillating masses allow the use of softer valve springs with the same speed stability. Friction is reduced because bucket tappets tilt in their guides when the cams run up and build up lateral forces. Due to the convex contour of the rocker arm, optimal valve lift curves for low pollutant values ​​and high torque can be achieved. Low side forces also reduce wear on the valve guides thanks to the use of hemispherical valve adjustment plates between the rocker arm and valve stem. The only disadvantage: more effort and
thus higher manufacturing costs.
In order to guarantee the best possible lubrication of the valve train, the oil from the hollow-bored camshafts squirts directly onto the base circle of the
Cam and builds up an effective lubricating film there. To prevent the oil in the valve train from foaming, it is collected in a deep chamber below the exhaust camshaft and fed directly to the suction pump for dry sump lubrication via a channel. From there, the lubricant reaches the oil tank via a cooler placed in the front panel, which is inserted into the frame triangle above the swing arm bearing.
The oil supply to the crankshaft is unconventional; the Formula 1 department was also advised here. Oil is pressed into the side of the crank pin and then, supported by centrifugal forces, reaches the lubrication points of the 38 millimeter main and connecting rod bearings (drawing on page 24). This allows the use of narrower, through bearings without an oil groove. It goes without saying that the crankshaft rotates in a space sealed off from below in order to minimize slipping losses and oil foam formation.
For the best possible combustion, the K engine is compressed to an impressive 1:13. However, this is only possible because the knock control immediately detects any ringing and adjusts the ignition timing and injection quantity accordingly for each cylinder. BMW can afford everyone through this monitoring system
To release gasoline types. However, with the advice that the use of regular gasoline will result in a slight loss of maximum performance.
The other engine management is very interesting: While the competition today uses injection systems with double throttle valves for better control, BMW leaves it with a single, 46 millimeter large throttle valve per cylinder, which is operated conventionally by gas cable. The secret lies dormant, an electronically controlled servomotor turns the position of the throttle valve back on its shaft if the throttle grip is torn too hard, without the driver noticing it.
In this way, the throttle response, load change shocks or even too brutal acceleration with slip on the rear wheel can be corrected. Project manager Wolfgang Nehse did not want to reveal which parameters this control system, which is also used in some MotoGP machines, controls.
On the other hand, there are no secrets when it comes to the substructure of the new oven
cylinder, which is very narrow with a width of only 480 millimeters. As in the Yamaha YZF-R1, the alternator and starter are piggybacked over the gearbox. Bmw does not undertake any experiments with the problematic bearing of the piston pin: The pressed-in bronze bushing with good emergency running properties is still the most solid solution, while Japanese engine manufacturers mainly rely on the inexpensive but critical steel-on-steel bearing. A minimum mileage of 100,000 kilometers was the specification for the designers.
The Bavarians tackle annoying vibrations with two needle-bearing balance shafts that are driven directly by a toothed cam disc on the crankshaft. They rotate at twice the engine speed and thus eliminate 100 percent the high-frequency vibrations caused by second-order inertia forces. To prevent further unpleasant vibrations and sound emissions from occurring, a drive unit with elastomer elements, similar to a shock absorber in the rear-wheel drive, is located between the gear wheel and counterweights.
A multi-plate oil bath clutch, a novelty at
the BMW multi-cylinder engines, the engine power is transferred to the six-speed cassette transmission. This is mounted laterally in the transmission tunnel, including the aluminum shift drum,
to which the 90-degree angle drive for the cardan shaft connects On the left.
The weight of the new BMW four-cylinder, including all ancillary units and the cardan, is around 81 kilograms-
diversion for the sport touring category is low. To the
Comparison: 1000 series super sports engines weigh around 60 kilograms. The K cannot stand up to the current lightweight bullets with a total weight of less than 200. But that is not what the new K 1200 S drive is for, according to project manager Nehse
thought. It remains to be seen how the visibly high effort is noticeable in practical driving, the first impressions (MOTORRAD 17/2004) were very positive. The top test of the new BMW K 1200 S will ultimately clarify what the technological boost will bring.

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