Rod Bearings
Precision-split shell bearings positioned between the connecting rod and the crankshaft journals.
Rod bearings (connecting rod bearings) are precision-machined half-shell inserts located in the big end of the connecting rod where it clamps onto the crankshaft's rod journals. They allow the connecting rod to rotate smoothly around the spinning crankshaft.
The bearings do not touch the crankshaft directly; instead, a thin film of pressurized engine oil is fed between the bearing and the journal, creating a hydraulic cushion that prevents metal-on-metal wear under heavy combustion loads.
If the engine suffers from low oil pressure, contaminated oil, or oil starvation, this protective oil barrier breaks down. Metal-on-metal contact will quickly wear away the soft bearing material, leading to a loud, rhythmic knocking noise known as 'rod knock' under acceleration.
A severely worn or spun rod bearing can cause catastrophic engine failure by locking up the crankshaft or breaking a connecting rod. Replacing rod bearings requires dropping the oil pan to access the rod caps.