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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.

The authors have utilized a modified automobile engine with a transparent glass cylinder, which was driven by an electric motor. The effects of the positions of the piston ring gaps, the end clearance size and the shape of the piston ring gaps on the lubricating oil flow were examined using the modified engine. The results indicate that the main stream of the lubricating oil flow goes from the lower ring gap to the upper ring gap in all of the positions of the piston ring gaps and that the position of the oil ring upper side rail gap has a great influence on the lubricating oil flow.

The authors have constructed a modified engine with a transparent glass cylinder, for motoring experiments, to observe lubricating oil flow from the sump to the combustion chamber through the clearance between the piston and the cylinder. The modified engine was motored at engine brake condition and the oil flow was filmed by a video camera. The amount of actual oil flow was also measured. The effects of pressure difference between the intake manifold and the crankcase, oil temperature, and oil ring tension on oil flow through the piston ring belt were studied. The results indicate that the main stream of oil flow increases with pressure difference and with oil temperature, and that oil flow is increased when a higher tension oil ring with excessive spacer expander circumference is utilized. Measuring equipment was also developed to examine the deflection of the oil ring underside in the cylinder when the expander circumference was varied.

During the scavenging of a two-stroke engine, it can be assumed that a very small quantity of fresh mixture flows from the scavenging ports and also from the crankcase through the gap between the cylinder and the piston to the exhaust port, in order to assess the effects of these leakages on fuel economy and hydrocarbon emissions, the authors calculated the quantity of mixture lost using the time-areas of the flow paths and the pressure-time history in the crankcase, and found that this quantity was in the order of 1-3% of the inducted fresh mixture.

Using a modified engine with a transparent glass cylinder for motoring equipment, the effects of the structure in the vicinity of the oil ring groove drain back slots of the inside of the piston, the end clearance size of the oil ring side rail gaps and the shape of the top ring gap on the lubricating oil flow were examined. The results indicate that the amount of undesirable oil flow was reduced by utilizing a piston with the covers installed under the drain back slots on the inside of the piston, the side rails with the optimized upper and lower side rail gap size and the top ring with a special joint (triangle step joint) as compared to a standard piston and standard piston rings. Furthermore, the amount of undesirable oil flow was considerably reduced by utilizing the combination of the modified piston and rings.