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Design BMW R 1250 GS

GS with double cam

The new BMW GS will be presented at the end of 2010. MOTORRAD is already daring to look ahead and can rely on a few facts. A boxer engine with double-cam cylinder heads is considered safe.

D.he BMW HP2 Sport is not just a sporty, elegant motorcycle. It looks like a window into the future of the boxer engine. In order to achieve its power of 133 hp and, above all, the necessary speeds, it was given cylinder heads with two overhead camshafts, which each operate four radially arranged valves via rocker arms. A lighter, more speed-stable and, because of the possible efficient cam profiles, also more powerful than the current solution, each with a high-lying camshaft, short push rods and rocker arms. The BMW engineers never left any doubt that this mechanical gem would not be reserved for an exclusive model. Their elaborately CNC-milled inlet section would, however, be too expensive for the production of larger quantities, so it was heard. But even with raw ducts and smaller cross-sections for more torque in the lower and medium speed range, the dohc head can give the boxer a powerful boost in performance. Over 120 PS with good exhaust quality and homogeneous power delivery – that’s how MOTORRAD values ​​it.

Design BMW R 1250 GS

GS with double cam

BMW R 1250 GS with probably 1228 cm³ displacement

Exactly the performance that a future GS may need in view of the approaching competition from Yamaha. The R 1200 S (122 hp) already has this limit with the "old" Cylinder head exceeded, but at the expense of a questionable characteristic: Downstairs it went listless, then the performance began comparatively violently. Not the right thing for the GS. As far as displacement is concerned, the four-valve boxers have so far increased from generation to generation – actually by 45 or 40 cm3, respectively by 50 cm3. It is therefore likely that future boxer models, whose pilot motorcycle will of course be the GS, will be called the R 1250, although not all BMW technicians are convinced of the increase in displacement. The future exhaust gas regulations are more and more difficult to create with larger individual cubic capacities, especially with larger bores due to the extension of the flame paths, explained a skeptic. He will probably have to bow to the requirements of marketing on this question.

Artist

Numerous divergent lines cause some unrest in some parts of the current GS.

In addition, the dohc cylinder head is distinguished not only by the better valve train, but also by a more favorable combustion chamber shape, thanks to the radially arranged valves, which promotes the rapid burning of the mixture. 2.5 millimeters more drilling, i.e. 103.5 millimeters, is possible under these conditions.

Ducati has long been operating with the 104 and the 1098 R and 1198 models with 106 pistons, the engines of the Harley V-Rod models measure 105 millimeters, just as much as the V2 of the KTM RC8 R. Morini dares even 107 Millimeter hole . Because the blank of the boxer crankshaft does not allow the stroke to be increased, it will probably remain at 73 millimeters. With a 103.5 millimeter bore, this results in a displacement of 1228 cm3. It is rather unlikely that BMW will design a new crankshaft. The current one has even proven itself in armed engines at 24-hour races, and a new one would be expensive. This would run counter to the iron law that stands above the K 35 project – according to the presumed coded of the BMW R 1250 GS development: The new one must be much cheaper to produce than its predecessor. A truism, of course, but one that has been confirmed and emphasized by a BMW insider.

Big design changes unlikely

This announcement leads to the question of where production costs can be saved on the BMW R 1250 GS without reducing the processing quality. In spite of all the cost pressure, BMW could not allow itself to do that with the largest sales generator in the model range. One possibility is offered by modern die casting technology, as used by Japanese manufacturers. The photo of the rear frame of a Honda CBR 600 RR shown above shows the complex constructions that are possible with this process; A frame made of such profiles could replace the previous tubular structure of the Boxer BMW with the many welded joints of cast, sheet metal and pipe parts. The GS alone is produced in such large numbers that the molds would be profitable. With each additional R model, the investment country for itself even faster. In addition, there is the option of having the frame cast in China, as is already the case with the bikes of the current GS.

For the rear frame, which is often heavily loaded with a pillion passenger and large luggage, BMW should stick to a tubular steel construction in favor of travel suitability. It is tougher, more elastic and easy to weld if it breaks. Major changes to the design of the BMW R 1250 GS are not expected. She has such an outstanding rank that her outward appearance is better looked after only with care. Stefan Kraft, the creator of the MOTORRAD design, has slightly retouched the headlight arrangement and the duckbill and optically tidied up the area around the tank and airbox by allowing the lines to run in only two main directions. The yellow part behind the BMW logo is used to quickly attach a tank bag. Kraft also cleverly uses the flatness of the aluminum profiles to hide the technology, which in some places in the tubular space frame of the current model is jagged and unsorted.

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