BMW - Helical Gearbox


The new generation of BMW models is fitted with a gearbox that enables both light and precise gear shifts. The cogs of the six speed gearbox, e.g. in the current flat twin models, are helical, ensuring lighter and more precise shifting and a significant reduction in running noise compared with conventional gearboxes. The compact housing fits in between the engine and the secondary drive (swing arm with integrated shaft). The entire gearbox weighs just thirteen kilograms. The highly rigid helical gearing not only means the cogs run more smoothly due to the softer meshing, it also means the individual gears engage more gently. This precision can be clearly felt during gear shifts. In conventional motorcycles, the gear shift takes place when the cogs shift on the shafts, whereas in the helical gearing system of the BMW Motorrad gearbox, it takes the form of a constant mesh transmission with three sliding sleeves: the cogs are therefore constantly intermeshed and activated indirectly. The advantage of the sliding sleeves is that they are lighter and narrower than shifting cogwheels, so they can be shifted more easily across the shift forks and shafts. Thus the shift distances are very short and precise. To improve weight optimisation and ease of operation, the gear selector drum is hollow and supported by ball bearings. The idler gears are mounted on low friction needle bearings, and the shafts on ball bearings. These are so-called “clean bearings” which prevent penetration by particles. Maintenance intervals are thus extended: The gearbox oil needs to be changed only every 40,000 km. The gearshift shaft emerges from the left of the housing. The gearshift linkage can therefore be laid more easily to the gear lever at the footrest. The optimum stepping with an active, short ratio sixth gear provides impressive pulling power. The gearbox is fitted as standard with a potentiometer that allows the individual gears to be shown on the multifunction display. For the optimum maintenance, the potentiometer can be replaced with the gearbox still installed.