Piston ring functions — specific role of the oil-control ring Which statement best describes the function of an oil-control ring in a piston assembly?

Introduction / Context:
Piston rings are typically arranged as two compression rings and one oil-control ring (sometimes multi-piece). While compression rings focus on gas sealing and heat transfer, the oil-control ring manages lubrication on the liner to minimize oil consumption and smoke.

Given Data / Assumptions:

• Four-stroke passenger car engine.
• Conventional ring pack with drain-back holes in the piston ring groove.
• Normal oil viscosity and operating clearances.

Concept / Approach:
The oil-control ring scrapes and meters oil on the cylinder wall during piston motion. Excess oil is collected through ring slots and returned to the crankcase via drain holes. By preventing oil from migrating into the combustion chamber, it reduces oil burning, deposits, and HC emissions while ensuring a thin film remains for lubrication.

Step-by-Step Solution:

Verification / Alternative check:
Engines with worn oil rings show blue smoke, high oil consumption, and fouled plugs/catalysts. Restoring oil-control ring function cures these symptoms.

Why Other Options Are Wrong:

• Releasing oil: rings do not dispense oil; they meter and return excess.
• Only holding oil in a channel: incomplete; the key is scraping and returning.
• Gas sealing: primarily the role of compression rings.
• Heat transfer to the pin: rings transfer heat to cylinder walls, not specifically to the pin.

Common Pitfalls:
Installing expander-type oil rings upside down; blocked drain holes causing oil pumping; using incorrect oil viscosity.

Final Answer: