A Cam is a rotating part that is purposely made not round. The contours of this part are used to push an adjoining part away from the cam's axis. Most commonly cams are found in two places on a moped. The first is the ignition, here it is attached either to the flywheel or crankshaft and used to open and close the points. The second place is on a drum brake system. In this case the cam is nearly rectangular and situated between the brake shoes. As the cam is rotated into a position that approaches lengthwise between the shoes, the shoes are forced apart. In the rare occasion that a moped has a four stroke engine cams are used to operate the valves.

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