Which lubrication method is correct for large four-cycle engines?

• A. Splash lubrication
• B. Oil, fed under pressure by a pump
• C. Oil rings
• D. Oil pre-mixed with fuel

Answer: (B)

Large four-cycle engines need a reliable, controlled supply of oil to all moving parts, including main bearings, crankpins, and cam-train components, at varying speeds and loads. A pump-fed, pressurized lubrication system delivers oil through dedicated galleries and passages, maintains a steady oil film, and allows filtration and cooling before the oil returns to the sump. This ensures consistent lubrication even under high-speed operation and heavy loading, reducing wear and preventing bearing damage.

Splash lubrication relies on oil being flung around by the moving parts, which can leave some bearings underfed at higher speeds or with larger engines. Oil rings are just components that control how oil is returned or scraped from surfaces and do not provide a full lubrication system. Oil mixed with fuel is a method used for two-stroke engines to introduce lubricant with the fuel, not for the separate, pressurized lubrication needed in large four-stroke engines.