As many of us would have seen, piston rings are not a continuous circle. They have a cut, so that it can be mounted in the piston ring grooves. When in place and piston sliding in the cylinder, there still is a gap in the piston ring ends. Why? To make sure when they expand after getting heated up, they dont start touching each other and force the ring to break. In bigger engines, this clearance is checked. It is called Butt Clearance. It is very important to have a certain minimum value of this clearance, else the rings will break or damage the cylinder in no time. In cars, it is very difficult to measure this. I dont know whether it is measured or not.
How do piston rings seal? First of all, they are manufactured in such a way that they maintain their spring action throughout there life. And gas pressure plays a vital role in sealing process. Gas enters the groove and pushes the rings outwards, ensuring proper sealing during power stroke. Inspite of all this, there always is slight leakage of gas into the crankcase. This is the reason why carbon content in oil increases with usage/time.
How do piston rings seal? First of all, they are manufactured in such a way that they maintain their spring action throughout there life. And gas pressure plays a vital role in sealing process. Gas enters the groove and pushes the rings outwards, ensuring proper sealing during power stroke. Inspite of all this, there always is slight leakage of gas into the crankcase. This is the reason why carbon content in oil increases with usage/time.