EX­PERT’S GUIDE TO... GEAR­BOXES

Dogs, cogs, forks and gears – just what is go­ing on within the depths of your bike’s gear­box?

Motorcycle News (UK) - - GARAGE -

Your gear­box is one of the for­got­ten he­roes of the en­gine. A mod­ern bike has to be able to work seam­lessly over a huge range of speeds, from climb­ing a hill two-up, to cruis­ing at mod­ern mo­tor­way speeds, or lap­ping a race­track. Chang­ing the gear­ing of the en­gine is the only way to give this flexibility.

In­side a mo­tor­cy­cle gear­box are two shafts; an in­put shaft driven by the en­gine’s clutch and an out­put shaft that is con­nected to the front sprocket or shaft drive. These shafts carry gears of dif­fer­ent sizes, just like a bi­cy­cle. Al­ter­na­tive gears are freely ro­tat­ing on the shaft, they get drive when they need it from a neigh­bour­ing gear that is fixed to the shaft, but can slide into con­tact with the freely ro­tat­ing gear, via teeth on the side called dogs. Only one in­put and one out­put gear are meshed at any one time, giv­ing drive to the rear wheel.

When you press or lift the gear lever this ro­tates the grooved se­lec­tor drum. The grooves move se­lec­tor forks that sit in be­tween the gears, dis­en­gag­ing the cur­rent gears and push­ing two more to en­gage, which feeds in the next gear.

In this case, an ex­ploded gear­box is a good thing as it means you can see its in­ner work­ings

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