A motorcycle sprag clutch, also known as a one-way clutch or a starter clutch, is a mechanical device used in motorcycles to transmit torque in one direction only. It is primarily found in the starting system of motorcycles with electric starters.
The sprag clutch consists of several sprags or rollers that are held in place by a cage or race. The sprags are shaped in such a way that they can engage with the inner race when it rotates in one direction, but they disengage when the rotation is reversed. This design allows the sprag clutch to transmit torque from the starter motor to the engine's crankshaft during the starting process, but it prevents the engine from transferring torque back to the starter motor once it is running.
When the starter motor is engaged, it rotates the inner race of the sprag clutch, causing the sprags to engage and drive the engine's crankshaft. Once the engine starts running and its crankshaft rotates faster than the starter motor, the sprags disengage and allow the starter motor to spin freely without being driven by the engine.
The sprag clutch is an important component in the starting system as it prevents damage to the starter motor by disengaging it once the engine is running. It also ensures that the engine does not turn over the starter motor during normal operation.
If a sprag clutch fails, it can result in starting issues, such as difficulty starting the motorcycle or a grinding noise during the starting process. In such cases, the sprag clutch may need to be replaced or repaired to restore proper functionality.