Various reasons internal combustion engines wear out quicker than an engine run by steam (external).

Internal combustion gasoline engines wear out so rapidly, compared to a steam engine, that it almost seems they were designed that way. The ways an internal combustion gasoline engine can wear itself out are numerous:

Carbon Formation
In an internal combustion engine unburned gasoline forms carbon in cylinder heads and on piston tops. When you hear an engine knock or “ping” the cause is quite often a hot piece of carbon igniting the fuel-air mixture at the same time the spark plug fires. The resulting noise is caused by the flame fronts colliding in the combustion chamber. Much of this occurs below the level of human hearing.

Valve Springs
Valve springs can wear out and lose their tension, especially if allowed to remain fixed in one position for too long, as when a car is parked for months.

Poppet Valves
The steam engine in the photos uses a slide valve. I.e., it slides back and forth over a smooth surface. Normal car valves bang against their valve seats and wear accordingly.

Piston Rings
High rpm and side-loading cause high wear.

A steam engine will almost never operate at temperatures of over 800 degrees Fahrenheit. The temperature generated in a gasoline engine will almost never go below 2,200 degrees Fahrenheit. Heat is a major wear factor.

Steam engineers designed their engines to last. No one has ever accused gasoline engine designers of the same goal.

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