What characteristic do "tri-metal" engine bearings have?

Tri-metal engine bearings are designed with a specific structure that enhances their performance and durability under the demanding conditions of an engine. The defining characteristic of tri-metal bearings is their layered construction, which typically includes a thin layer of babbitt—a soft metal alloy primarily made of tin, lead, and antimony—coated over a copper/lead layer that is, in turn, supported by a steel shell.

The babbitt layer provides a smooth surface that is crucial for minimizing friction between the bearing and the journal of the crankshaft, thereby reducing wear and promoting fluidity in high-speed operations. The copper/lead layer acts as a cushioning barrier that also helps with the distribution of load and improves the overall load-bearing capacity of the bearing. Meanwhile, the steel shell provides strength and stability, ensuring that the entire assembly maintains its shape and does not deform under high pressure.

This combination of materials is what makes tri-metal bearings particularly suitable for high-performance engines, as they can effectively handle both high temperatures and varying load conditions, contributing to the engine's longevity and reliability.