Nakashima, K., Murakami, Y., Yamamoto, M., and Ishihara, S., "Projection Behavior of Piston Rings in Cylinder Ports of a Two-Stroke Cycle Engine," SAE Int. J. Engines 6(1):204-208, 2013, doi:10.4271/2013-01-0295.
Two-stroke engine cylinders have ports to exchange gas. While the engine runs, the piston and its piston rings slide over these ports in the cylinder walls, and the rings may project into the ports. This paper explores this, first, by reporting a simple model of material mechanics that predicts rings might project into ports, and second, our experimental verification. We installed strain gauges on the bottom of the top and second rings, over the intake and exhaust ports, and ran signal wires out of the engine. We then examined the variations of strain while running the engine. Our analysis confirmed how the dimensions and the tension of the rings, and the dimensions of the ports, affect ring projection into ports as static displacements. Our measured ring strain suggests that, on the upward stroke, the top and second rings indeed project into the exhaust port; while the top ring catches in the upper side of the exhaust port, and the second ring catches in the upper sides of both intake and exhaust ports.