2007 BMW G 650 Xchallenge
The new G 650 models were developed in association with Aprilia and are manufactured in Italy. The engine is built by Rotax to BMW specifications. The new BMW G 650 Xchallenge is designed for trail riders who want an exciting, lightweight and high performance machine.
Powertrain.
The engine is a weight optimised development of the familiar liquid cooled, fuel injected F 650 GS engine, now 2kg lighter. Engine output increases by 39 kW at 7,000 rpm. Torque is 60 Nm at 5,250 rpm, and the engine complies with EU 3 restrictions on emissions. With a 100mm bore and 83mm stroke, the capacity is 652cc exactly. The double overhead camshaft drives two intake and two exhaust valves, while twin spark plugs extract maximum torque. The second plug is retarded slightly at higher revs to ensure a cleaner burn. A die-cast aluminium crankcase holds the crank in plain bearings and other shafts run in ball bearings. A balance shaft virtually eliminates typical 650 single cylinder vibrations. The new dry sump lubrication means a very small oil pan, with two pumps in the side of the block; the smaller to pump oil around the engine and the larger to pump returned oil through the filter. The wet clutch has seven friction and seven steel plates. The magnesium clutch cover is painted black, as is the redesigned alternator cover. This gives the G 650 engine a different look to that of the F 650. The familiar dual-shaft five-speed gearbox is of conventional design, and it drives the rear wheel via an O-ring chain. Final drive ratio on the chain sprocket has been modified compared with the reliable F 650, with a 15-tooth pinion and a 47-tooth sprocket fitted to the G 650 Xchallenge. Thanks to the very frugal and efficient engine, the 9.5-litre fuel tank gives a range of 200km plus, depending on riding conditions. Service intervals of 10,000km are unusually long for this class of motorcycle, under-lining its inherent durability.
Chassis
The G 650 Xchallenge uses an all new chassis and suspension designed for excellent riding off-road. A standard aluminium sump guard is bolted to the underside of the engine, underlining its taste for off-road work. The suspension comprises top grade components including upside down telescopic forks with 270mm travel. The 45mm stanchions move within gold anodised sliders and are protected against dirt and wear by black plastic covers. The rear air suspension strut also allows 270mm of travel. The BMW Motorrad Air Damping System delivers a pneumatic rear air suspension strut similar to that of the BMW HP2 Enduro. For the G 650 Xchallenge damping and suspension are determined by air pressure only. Two damping levels may be selected via the adjuster and the height of the bike is determined by air pressure inside the strut. A standard valve (tyre type) allows the air pressure to be regulated, and a pump is clipped under the seat. During compression and rebound, air travels through defined passages between the cylinder space and rubber bellows. Compression of air creates a progressive suspension as far as the elastic, plastic bump stops.
Benefits of the BMW Motorrad Air Damping System are:
_ "Natural" progression of spring rates under high load (with growing pressure within the system).
_ Reliable and smooth operation minimising the risk of the suspension giving way (physical law of gases: pressure increases as a function of temperature).
_ "Natural" progression of the damping effect under high loads (the viscosity of air increases as a function of temperature).
_ Frequency-dependent, selective damping effect.
_ Resistant to overheating (no temperature-induced weakening of the damping effect under high loads).
_ Simple option to adjust the dampers to the load carried.
_ Low weight of the entire system and its components.
_ Individual adjustment and set-up of the suspension matched to the rider’s weight and the load carried by means of a spirit level presenting the normal position and trim of the motorcycle.
_ The reduction in unsprung masses also improves spring response and traction on the rear wheel. The spring strut is sealed hermetically and is therefore protected from contamination. It can be re-pressurised simply via the hand pump carried on board.
Frame.
The split-bridge main frame is tubular steel, powder coated with a grey 'graphitan' finish. The engine is a load bearing unit. Reinforced high strength steel sections extending from the steering head are bolted to two cast aluminium mouldings and the cylinder head.
