Engine speed is limited mostly by valve action. Valve springs can only move so fast. When the cam lobe drops to close the valve, does the valve follow it? At high speeds it does not, and you get valve float, which really messes up things that are supposed to happen in the combustion chamber. You get flame in the intake manifold, loss of compression, blah blah blah.
That's why Formula 1 engines, and now most MotoGP as well, use pneumatic systems. The valve is closed by air pressure, not a metal spring, which allows the valve to follow the cam profile. Now you've made the bottom end the part that has to hold together.
Other engine speed problems are simply how much mass is moving, and how hard a force does it take to change that mass's direction of travel. Pistons go up and down, and connecting rods, wrist pins, and bearing have to take that load, on the order of 10,000 g's at the wrist pin (not a typo: 10 to the 4th power!) The conn rods actually stretch and compress under the load, and how much of that they can take determines when they come apart and go through the side of the block.
A Formula One engine has a very short stroke, around 40mm, specifically to limit the load on conn rods. The piston moves slower than an engine of longer stroke but smaller bore. With such a short stroke, even at 19,000 RPM the piston speed is about the same as a high-performance street car.
Engine failures aren't always parts failures directly. You have timing errors, oil loss, overheating, etc.
The obvious question is: Why do you need all those revs? Simple answer. RPM=Horsepower. The amount of power an engine produces is directly proportional to the engine's speed multiplied by the torque it produces at that speed.
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