Working of Motorcycle Clutch A simplified Briefing

Have you ever walked into a conversation between other bikers and they’re speaking another language with words like “fibres”, “plates”, and “springs”, yet you have absolutely no clue what they’re on about? Well, the topic is clutches – you know, the left-hand lever which allows your motor to transfer power into the gearbox and propel the bike forward. There have been a few variations of ‘clutches’ over the years of motorized two-wheeled vehicles, so we’re going to try and explain how they work.

If you’ve ever been lucky enough to lay eyes on a really old motorcycle like the harley’s from the turn of the 20th century, the first ‘clutch’ type system was a simple tensioner that adjusted the slack in the belt drive directly between the motor and the rear wheel. When it was loose, the belt would slip, and when tightened by a hand lever, it would grip on the drive pulley and engage the rear wheel. Before gearboxes made their way into motorcycles, this was a very simple, but effective method for modulating power out of the motor.
Most newer motorcycle clutch systems work in a fairly similar method, where one side of the clutch is connected to the motor and the other side is connected to the gearbox. Basically, a new clutch kit is a sandwich of steel ‘plates’ (blank steel discs) and ‘fibres’ (friction material bonded to a metal core disc) which is held together in a ‘basket’. The plates are ‘keyed’ around the inside diameter, and the fibres are ‘keyed’ around the outer diameter. The motor drives a splined shaft through the centre of the whole assembly, which is affixed to the plates. The clutch basket (the outer cage holding the whole assembly together) is structured to lock into the fibres. The alternating layers of plates and fibres are all pressed together with a spring-loaded pressure plate, on the open side of the clutch basket. When you pull the clutch lever in, the pressure plate moves fractionally away from the clutch basket, allowing the steel plates and fibres to slip between each other, disengaging the motor from the gearbox.
Did you get through all of that without your head exploding? Okay, picture this then: hold up your hands like you are about to clap. Imagine your left hand is attached to a motor (ie. a steel plate), and your right hand is attached to a gearbox (a clutch fibre). Both can turn unimpaired (you can wave with either hand) very easily. This is the ‘clutch pulled in’ scenario. Now put your hands fairly firmly together. You can still ‘slip’ your hands if you try hard enough, right? That’s because there isn’t enough pressure holding everything together, like when you’re slipping your bike’s clutch, accelerating away from a traffic light.

Now, get a couple of your friends to put their hands on the outside of yours like a multi-layered sandwich, and get everyone to push together. Now when you try and turn your hands in opposite direction, you can twist as hard as you like, but you can’t overcome the combined pressure of all the alternating ‘plates’ and ‘fibres’. Picture this as your clutch lever now being all the way out and everything is locked together. That’s exactly how a motorcycle clutch works.

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