WHAT ring prevents the majority of the expanding compression gases from getting past the piston into the crankcase?

The ring that prevents the majority of the expanding compression gases from passing the piston into the crankcase is called the compression ring. Typically located at the top of the piston, it creates a seal against the cylinder wall, ensuring that combustion gases remain contained during the power stroke. This helps maintain engine efficiency and performance by reducing blow-by, which can lead to oil contamination and loss of power.