Engine Bearing

What is an Engine Bearing

An engine bearing is a specially designed bearing used inside internal-combustion engines to support rotating components — most notably the crankshaft. In common piston engines, the “main bearings” cradle the crankshaft inside the engine block (the crankcase), allowing it to rotate smoothly while withstanding the mechanical forces produced by piston operation.

The internal combustion engine (piston engine) currently is still the most common engine used in automotive indutstry, even though the electric vehicles using electric vehicles are getting rapidly popular. Combustion engines contain several bearings and the one that allows the crankshaft to rotate is named as main bearing or engine bearing. The figure above shows the location of an engine bearing in a four cylinders combustion engine.

Bearing is a device that is used to reduce friction between moving parts of machine elements to provide movement in a desired way with minimum power losses. Development of bearings is one of the most revolutionary steps in the development of human made machines. First concept of a bearing was described by Leonardo da Vinci.

The main functions of bearings are:

• Reducing friction
• Supporting parts of the machine or machine elements
• Bearing radial or thrust laods

The function of the main engine bearings is to support crankshaft and allowing rotation during the engine operation. Main bearings are mounted in the crankcase.

How Engine Bearings Work — Principle & Design

Engine bearings (especially for crankshafts) typically use journal bearing design: two semi-cylindrical shell halves (upper and lower shells) that together surround the crankshaft journal.

At rest, the shaft might contact the bearing shell directly, but once the engine starts and oil is pumped through the system, the crankshaft begins to rotate and the oil is forced into the narrow gap — creating a hydrodynamic oil film. This film lifts and separates the journal from the bearing surface, enabling the crankshaft to “float” and rotate with minimal friction — often described as a “wedge” effect.

This oil film does more than reduce friction — it also acts as the primary medium for heat removal, protecting both bearing and crankshaft from thermal stress. If lubrication fails (for instance due to low oil pressure, contamination, or oil breakdown), the protective film collapses, leading to metal-to-metal contact, rapid wear (scoring, scuffing), overheating, and possible catastrophic failure.

Additionally, engine bearings are designed with layered materials: a strong backing (often steel) to provide structural support, with a softer overlay (e.g. a friction-reducing alloy) that provides a conformable, embeddable surface. This layered construction helps protect against surface imperfections in the crankshaft journal and allows the bearing to accommodate debris (small particles) by embedding them without catastrophic damage.

Some bearings also incorporate features like oil grooves or eccentric wall design (to promote oil flow and heat dissipation), helping carry away heat and flush out contaminants — essential for bearing longevity under harsh engine conditions.

Why Engine Bearings Remain Critical in Modern Engines

Even as the automotive industry gradually shifts toward electrification, internal-combustion engines remain widespread globally — especially in legacy vehicles, heavy-duty machinery, industrial engines, and many hybrid powertrains. The reliability and lifetime of these engines depend heavily on the quality of their internals — and engine bearings are among the most critical.

Moreover, modern engines are increasingly pushed for higher performance, greater efficiency, and tighter tolerances — placing even more demand on bearings to deliver low friction, high load capacity, excellent lubrication compatibility, and long-term durability. Advances in materials, coatings, and lubrication technology continue to make bearings more reliable, but their proper selection, installation, and maintenance remain fundamental.

Conclusion

The engine bearing is a small yet vital component — a true “unsung hero” — that enables smooth rotation, reduces friction, supports heavy loads, maintains alignment, and ensures longevity of the engine’s rotating assembly. Understanding how bearings work, how they’re built, and what conditions they require is essential for engine designers, mechanics, or anyone interested in engine performance and reliability.

By combining proper design (material, geometry, lubrication channels), precise machining, and diligent maintenance (oil quality, cleanliness, correct tolerances), engine bearings can maintain engine health for hundreds of thousands of miles — but neglect just one factor, and the consequences can be severe.