[Motofool]

Originally Posted by Rifleman

........... it would seem to be insanely difficult to make a ring that presses out against the oval cylinder wall equally or efficiently. The circle works, that flat spot in the oval, seems to me to be the place that the ring would be pressed against the cylinder the softest/least................

Copied from
http://world.honda.com/history/chall...ine/index.html

"The piston ring, also, was a real headache, since the oval shape was so difficult to machine accurately. Experiments were repeated over and over, through a process of trial and error. For example, they tested a split-type ring made of two parts and formed the ring into a "walking stick" shape. But after every conceivable alternative had been tried, they found themselves back at the starting point with a conventional, self-stretching piston ring. Even with that configuration they still had to expend extra effort calculating the appropriate dimensions, so that the ring would remain in free form during machining, but produce constant bearing pressure once installed. NC machines were still inaccurate during that period. Therefore, additional effort was required to produce the desired quality of a part by accurately reflecting the specified machining dimensions."