A power tool with a flywheel, an activation arm, a driver, a cam and a clutch. The activation arm can have a first arm, a second arm, which can be pivotally mounted to the first arm, and a roller that can be coupled to the second arm. The driver can be disposed between the roller and the flywheel. The cam can be moveable in a predetermined direction for causing the activation arm to rotate about a pivot to drive the roller against the driver so that the driver frictionally engages the flywheel. The clutch can cooperate with the cam to inhibit the cam from moving in a direction opposite the predetermined direction in response to a reaction force that is applied by the driver onto the activation arm.