Recently on Quora (a question-and-answer website based in Mountain View, California, where questions are asked, answered, edited, and organized by its community of users in the form of opinions) that this question was asked: “What engine is nearly indestructible?”
The Citroën 2CV air cooled flat twin was legendary for its durability. Why?
Well, the 2CV twin was designed from the crankshaft up for durability and minimal maintenance. It was a minimalist engine, designed around the mantra that: “If it is not there, it cannot break.”
Of course, being air cooled, it lacked a radiator, or a water thermostat, or radiator hoses, or a fan belt. The cooling fan was driven directly off of the crankshaft. On the original models the generator was also driven off the shaft that powered the fan. Thus, there was no accessory belt to break.
But the concept of designing to eliminate problem prone parts went further than that. In that era cylinder head gasket failures were common. It is still a problem today, 70 years after the first post-war Citroën 2CV was sold. The 2CV engine solved this by eliminating cylinder head gaskets! On the 2CV the cylinder barrels and the heads were precision machined and lapped to fit with a gas tight seal without the need for gaskets. Moreover, as Ian Hunt reminded me, you did not have distributor problems on a 2CV. It did not have one! It used a “wasted spark” ignition and simply fired both cylinders when they were near TDC (top dead center) on either the compression or exhaust stroke. Again, what is not there cannot break.
The same concept was used for the crankcase sections. Precision machining eliminated the need for gaskets. In some ways this minimalist concept was taken to absurd extremes. I drove a Citroën 2CV in which the windshield wipers (which were in perfect condition) would stop completely when I idled at an intersection in the rain. Why? Citroen had carried minimalism so far as to eliminate the windshield wiper motor entirely by driving the wipers with the same flexible shaft that drove the speedometer! [Ed note: That is why Citroën also provided a knob on the dashboard to manually operate the driver’s windshield wiper when the car was stopped.]
Quirky car. I could tell 2CV stories until I ran out of digital ink. But Citroën’s concept of minimalism resulted in an engine that would run forever anywhere from Antarctica to the Sahara with minimal attention on whatever fuel was available. It was truly an indestructible engine.