The Royal Enfield Bullet motorcycles, including models like the Classic and Thunderbird, use a wet sump lubrication system. A wet sump system is a common type of lubrication system employed in motorcycles and many other internal combustion engines.
In a wet sump system, the engine's oil is stored in an oil pan, or sump, located at the bottom of the engine. The oil pump draws oil from the sump and circulates it through the engine to lubricate the various moving parts. After lubrication, the oil drains back into the sump, where it is stored until it is picked up again by the oil pump for recirculation.
Wet sump systems are relatively simple and widely used in motorcycle engines due to their effectiveness and ease of maintenance. They typically require regular oil changes to ensure the engine is properly lubricated and to remove any contaminants that may accumulate in the oil over time.
It's worth noting that the lubrication system may have variations among different Royal Enfield Bullet models and engine configurations, but the wet sump system is commonly employed across the range.