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".
The camshaft(s) lobes push up on the rockers on top of the cylinders, which pushes down on the vavles, causing them to open
It refers to an engine where the area occupied by the valves when they are open is occupied by the piston when the valves are closed. If the timing belt lets go while the engine is running the piston will smash the open valves doing loads of damage.
The valves in a car engine are opened and closed by a cam shaft driven by the engine crankshaft. they allow the flow of gases and fuel into the engine and the burnt gases out of the engine into the exhaust system.
If the timing belt broke on an interference engine, the open valves and pistons would collide and wreck the engine.
A camshaft pushes against valves in your engine that allow air and fuel in, and exhaust out. This is important, otherwise the valves would not work as well and exhaust would build up, and it would be difficult to allow air and fuel in.
the 4.3 litre vortec V-6 is a pushrod engine. the camshaft is in the middle of the block, and it pushes rods that open and close the valves in the heads. it uses a timing chain to to turn the camshaft. so it has a timing chain
a cam in engine is to operate the lifters which in turn open and close the inlet and exhaust valves
overlap
Rocker arms, in conjunction with the camshafts, do so. The camshaft has an egg pattern on it, and this pushes the rocker arms up and down. The rocker arms are connected to the valves, and this puts the fuel/air mixture into the engine, then takes it out again
The cam pushes the lifter and pushrod up. The rocker sits on a fulcrum, which converts the upward motion of the pushrod into downward motion to open the valve.
Rods used in an Over Head Valve (OHV) engine to open and close the valves. They are moved by the cam and are about 8" long with a diameter of around 1/4". One end is pushed up by the cam and the other end makes contact with the rocker arms which rotates and pushes the valve open.
The cam sensor is a flat plastic thing with a coil of wire in it that tells the computer what position the camshaft is in. The shaft is a big rod with eccentrics on it also known as a bumpstick which pushes the engine valves open. It is the second largest rotating part in the engine. Do not break it.