I was thinking about how rings are manufactured and it all seems fairly straight forward, but how to they make the metal have that spring to it that holds pressure against the cylinder bore? I'm sure it's some sort of intentionally-induced stress in the metal before it's ever machined and cut open for the ring gap but how dey do dat?

 

The radius of the rings are larger than the bore that they are designed for.

That's why you need a ring compressor in most cases to install them.

 

It's not as straight forward as you might think. Just grinding the outside diameter is a challenge. How would you do that in a couple of seconds per ring?

Yes, a lot of what makes the ring work is the stress in the metal, and how that is managed. Some compression rings twist so that the bottom edge contacts the bore harder than the top. If you've ever installed a ring upside down you might figure out how "dey do dat."

 

It's not the tension that seals the ring in the bore. It is the combustion gasses getting behind the ring in the groove that pushes it agains the bore.

 

so I guess during the intake stroke the rings dont seal?

 

The tension does. But it's not as important because the ring doesn't have the combustoin pressure fighting it.