| In the installed condition (when the gap is closed), the piston ring must form a circle such that its periphery (running face) contacts the cylinder wall all the way around. This is a critical requirement. If the ring doesn't seal against the cylinder wall, combustion gases will leak to the outside. It's interesting to note that the ring does not press with uniform force all the way around its circumference, from one gap-end to the other. In fact, this contact pressure can be controlled during ring manufacture to guarantee that the desired contact pressure distribution is achieved in the assembled engine. The figures below show how the ring's contact pressure can be different, depending on the particular engine's specific requirements. |
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