Manual - Chapter 3 Gearbox

1. General description

The gearbox is a separate unit bolted on to the rear 'face of the engine unit and carries the clutch friction plate on its input shaft. Developed with and built for BMW by Getrag, the gearbox is a five-speed constant-mesh type which differs from general motorcycle practice in being all indirect, with a three shaft layout. The input shaft rotates on taper roller bearings which are preloaded in service by the addition of shims between the front bearing and a collar on the shaft. The shaft carries a two lobe face-cam shock absorber tensioned by a single coil spring to damp out transmission shock leads and transmits drive from the clutch to the output shaft via the layshaft.

These latter two shafts rotate in ball journal bearings and apart from the helical-cut top gear pinions, use straight-cut gears. The different gear ratios are selected by moving two pinions on the output shaft and one on the layshaft. These pinions are splined on to their respective shafts and have integral dogs which lock into corresponding dogs or slots in their neighbourinq pinions. thus locking the second pinion to the shaft to transmit the drive. The sliding pinions are controlled by selector forks which are guided by slots machined in a selector drum. The drum is rotated by a claw mechanism operated from the gearchange pedal and fitted with a sprinq-loaded positive stop roller arm, or detent arm, and a limiting pawl on the selector claw arm which rotates the drum to prevent overselection.

A spring-loaded ball provides the neutral detent mechanism and a switch on the outside of the rear cover transmits information about the selector drum position to the instrument panel where a green lamp lights when neutral is selected (ignition switched on) and a liquid-crystal display (LCD) panel in the tachometer (rev counter) face indicates which gear is selected.