Clutch

The clutch sits between the crankshaft and the gearbox and lets the rider connect or interrupt the flow of power. On most motorcycles it is operated with the lever on the left handlebar, via a cable or a hydraulic system. Pulling the lever disengages the clutch; releasing it lets the springs clamp the plates together again.

Most bikes use a wet multi-plate clutch running in engine oil: friction plates alternate with steel plates in a basket. Some bikes have a dry clutch, and scooters use an automatic centrifugal clutch. Many modern bikes add a slipper or assist function to reduce rear-wheel hopping on downshifts.

Signs of a worn clutch are slipping under acceleration (revs rise but speed doesn't), a high engagement point or dragging. Use oil rated for wet clutches (JASO MA/MA2) and check cable free play regularly.