Which ring provides a controlled film of oil to lubricate the compression ring?

The wiper ring is specifically designed to control the oil film on the cylinder wall and ensure a proper amount of oil is available to lubricate various engine components, including the compression ring. Its primary function is to scrape excess oil from the cylinder wall on its downward travel during the engine's cycle, thus maintaining an optimal oil film. This control helps to prevent excessive oil consumption and keeps the combustion chamber clean by minimizing oil entering the combustion area.

In contrast, the oil control ring is primarily responsible for regulating the amount of oil that remains on the cylinder wall to prevent too much oil from being consumed during combustion, and the expander ring serves to maintain the engagement of the oil control ring against the cylinder wall for effective sealing. The compression ring's primary function is to maintain compression in the combustion chamber and does not play a role in oil distribution. Knowing the individual roles of these rings helps clarify why the wiper ring is correctly associated with the lubrication of the compression ring.