The Cush Drive Delivering a Smooth Ride
There's a control system on your motorcycle that probably gets very little attention, yet it's an important contributor to ride quality. It's your motorcycle's cush-drive system, and its job is to smooth driveline lash when getting on and off the throttle, and so soften the power pulses transmitted to the rear wheel from the crankshaft.When a piston pushes down on the connecting rod during the power stroke, it does so with a violent shock. The flywheel's mass smooths some of this shock, but if the remainder of the force generated by these power pulses goes unchecked, it can make your ride uncomfortable, as well as damage driveline components.
Cush drives use either rubber dampers or spring-loaded mechanisms to soften driveline shock. The most common type is the rubber cush drive and it's located within the enlarged portion of the rear wheel hub, behind the rear sprocket. In a motorcycle with a cush drive, the rear sprocket is bolted to a removeable carrier, which interlocks with rubber dampers inserted into the wheel. Power is transferred to the wheel through the rubber dampers, and it's the dampers' pliancy that absorbs the power-pulse shocks.
This is why, if you have an older motorcycle, you should inspect the dampers any time the rear wheel is removed. These dampers harden with age and can eventually even crumble to pieces. They also compress with age, introducing a lot of free play between the sprocket and wheel, and subsequently a lot of driveline lash. This is very easy to diagnose without removing the wheel: just hold the rear brake and, with the engine running and the motorcycle in gear, slowly release the clutch. If the rear sprocket rotates freely for several degrees before stopping, the rubber dampers are worn out.
You can extend the service life of the rubber cush drive by using silicone spray to lubricate the rubber dampers when assembling the sprocket carrier. However, don't use any type of grease, as it might swell the rubber, but more importantly, it will collect dirt, which will cause damage to the hub and rubbers.Despite its importance, not all motorcycles have cush drives. Dedicated off-road motorcycles. Like motocrossers and some enduros (mostly not street-legal), do not have a cush drive. Manufacturers deliberately leave it out on these motorcycles to reduce weight. However, engineers still account for some form of shock-absorbing capability, and it comes from an unlikely source: because these motorcycle ae designed to be ridden primarily off-road, it's the lack of traction on dirt that damps the engine's power pulses.
If you convert one of these motorcycles for road use, just bear in mind that you'll probably experience premature chain and sprocket wear, and even see wear on the transmission output shaft, so inspect everything often.Tag: Cush-Drive Driveline Power-Stroke Sprocket-Carrier Sprocket Chain Dampers Shock-Absorbing Rubber-Dampers
