That could see them hit the piston or push the intake charge back out the intake. That's called valve float, since they float, or stay open when you don't want. Spin them too fast, and the valve springs are no longer strong enough to close everything in time. Back and forth about 50 times a second at 6,000 rpm. The parts might weigh just a few ounces each, but it ads up.

The disadvantage of those lifters and long rods is weight. It also makes sure you don't end up with that nightmare of a chain that certain Audi engines had a few years back. That makes it cheaper, and more accurate. That proximity also means that the chain (or in rare cases belt) to drive the cam is shorter. There are fewer complex parts since you need just one cam instead of two or four, and the camshaft sits in the otherwise useless space in the middle of the vee. Adjusting the rocker arm and adjustment in the oil-filled hydraulic lifer means that the arms don't even have to be exactly the right length. Then a spring pushes the valve closed when the rod isn't trying to open it. The other side of that arm pushes the valve open.

In the head, it pushes one side of a rocker arm. From that camshaft, a lifter, well, lifts the pushrod, which is really just a rod of metal with a hole in it to allow oil to flow through, makes the long journey to the cylinder head. Pushrod engines have the cam in the vee of the engine (we're also sticking with vee engines here). We'll call them pushrod engines for the purposes of this piece. Since the camshaft is located firmly inside the engine block, and not inside the cylinder head like the overhead cam types. Some people call them cam-in-block engines, which might be the most appropriate. So you'll also hear them called 'pushrod engines' though there are DOHC engines that can have pushrods (looking at you, Roger Penske!).

It's been a long time since flatheads were at all common, and both types of overhead cam engines also have valves located over (at the top of) the cylinder head. The overhead valve engine's name is a bit misleading these days.

Push rod vs overhead cam