Even with good lubrication, piston rings, big and small end bearings, crankshaft bearings, valve guides, and numerous other bits and pieces of the engine eventually wear out. Constant rotation, heating up and cooling down, plus metal fatigue, all play their part, although good maintenance, especially on the oil front, reduces the wear factor, in particular during start-up. Even engines not used for a long period of time can suffer damage, with the pure weight being placed on one point of their bearings causing damage, which was I know especially true of the German Tiger tank during WW2. They had to be turned over regularly to avoid damage. There are no doubt other examples, which perhaps others can quote. But, although this is a thread about the internal combustion engine, I have got to mention the steam railway engine, which also undergoes the same wear and tear, and will also destroy itself by just sitting on its bearings too long.
However, all engines will eventually expire, the way its been treated deciding when! To my knowledge no one has yet designed an engine that can last forever, which of course would not be desirable as development to ever more efficient engines would not take place, killing off the industry!!
No, like with the human body, and I suppose everything that man produces, it is all designed to life expire at some stage due to the natural world around us that consists of friction, gravity, and changes in temperature.
