I wrote a start to finish narrative on how the whole engine works, but here's the transmission section which goes nicely with those slides:
Power from the engine is fed through the clutch center hub to the transmission mainshaft which has spline-driven gears that can be shifted to various positions resulting in different ratios between the input (mainshaft) and output shaft (layshaft). Power is transmitted from the mainshaft, through whichever gear pair is selected, to the layshaft, which turns the final drive sprocket, which drives the final drive chain, which drives the rear sprocket, turning the rear wheel.
The gear selector apparatus is a somewhat intricate assembly of pins, springs, pawls, cam and forks that operate thusly:
When the gearshift lever is depressed, a pin in the mechanism, that slips into a roller, that sits captive in a semi-circular “cup” in a gear-like apparatus that pivots on another pin, rotates slightly. The gear-like apparatus’ opposite end causes a camplate gear to rotate on it’s shaft. The front side of each of the two shifter forks has a pin; these pins wend their way through two curvaceous grooves cut in the face of the camplate as it rotates.
The two gear selector forks slide left-to-right on a shaft, with the tines of one fork riding captive in a groove of one gear on the mainshaft, and the tines of the other fork riding captive in a groove of another gear on the layshaft. So, as the gearshift camplate rotates, it moves the position of the appropriate gears one way or another, via the shifting forks, to align each matched pair in succession as the gears are selected. Regardless of the gear selected, power comes in through the mainshaft, feeds the selected drive gear, which feeds it’s paired driven gear, which feeds the layshaft, which feeds the drive sprocket.
