21 Page – PDF Download – Complete Series – BSA Gearbox Stripdown
“Understanding the gearbox
Tony Jones of OTJ kicks off a three-part series by explaining the workings of a much-abused and neglected item.
In the next two parts he strips and re-assembles a BSA gearbox.
Most British gearboxes are of similar layout, essentially simple, reliable, uncomplaining, and therefore often neglected. They don’t rattle, pink or seize or emit clouds of oily exhaust so the ‘out of sight, out of mind’ attitude prevails and is encouraged by nagging doubts about what those cogs and springs and things actually drive do.
So here it is – the beginner’s guide to the mysteries of the countershaft, constant mesh gearbox: or, put more simply, two shafts carrying pairs of gears (usually four) whose teeth are always in mesh with one another even when it is not their turn to transmit the drive.
Your typical British box has the mainshaft (rotating whenever the clutch on the end of it is engaged) concentric with the output ‘shaft’ which is therefore hollow; has a gear on the inside end of it and splines to take the final drive sprocket on the outside.
This is commonly referred to as the sleeve gear or sometimes the top gear since the highest gear is conveniently obtained by locking the mainshaft and sleeve gear together – one revolution of the clutch producing one revolution of the gearbox sprocket.
In top gear the rest of the gears whirr round unloaded and the gear reduction between engine and rear wheel is related on to the number of teeth on the four sprockets involved (engine, clutch, gearbox and rear wheel).”
Read all three parts of the BSA Gearbox Stripdown in this 21 page complete series.