When making a real steam engine you use piston rings, you don't really machine to exact tolerance except where you're showing off how precise you are. The rings

When making a real steam engine you use piston rings, you don't really machine to exact tolerance except where you're showing off how precise you are. The rings are consumable, they also flex since they're split rings (they're a C), which lets them expand as they wear. They're usually softer material or a slide compatible material with the cylinder walls. This makes them sacrificial and saves the much more expensive cylinder. You see them in literally every modern engine and I'm sure absurdly far back, even though they have better precision now. Your 1966 south bend is likely several orders of magnitude better than that emco, those things are more meant for wood, and imagine if you needed to align your spindle on your lathe every time you used it how inaccurate it'd be.