The cams on the camshaft.
NEW ANSWER : Yes it is the camshaft, But it is the LOBES on it that makes the valves open and shut. Not the Cams that's on it, No such thing.
Response to new answer: look up cam in a dictionary or on wikipedia. It's an irregular fitting on a camshaft that converts rotational motion to reciprocating motion. That said, the term "cam" is interchangeable with "lobe".
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