Engine > Bearings

About

Engine bearings are precision-fit components that allow rotating and reciprocating parts — crankshaft, camshaft, connecting rods, and balance shafts — to move with minimal friction inside the block and head. Most are plain sleeve-style bearings made from layered alloys (typically steel-backed with a babbitt or copper-lead overlay), while timing idler and tensioner bearings are roller-type. Connecting rod and main bearings are the most commonly replaced, usually due to oil starvation, contamination, or high mileage wear — symptoms often surface between 100,000–150,000 miles on engines with consistent oil changes, earlier on neglected ones. When buying, always match the bearing size to your crank journal dimensions — standard or undersized (0.010", 0.020", 0.030" are common) — and confirm the part fits your specific engine code, not just make and model. OEM bearings are a safe choice; reputable aftermarket brands like ACL, Clevite, and King offer comparable or better performance for high-mileage rebuilds or performance applications. Signs you need replacement Deep knocking or rumbling from the engine at idle that gets louder under load typically points to worn connecting rod bearings — often called "rod knock." This is a critical symptom that requires immediate inspection to avoid catastrophic engine damage. Low or fluctuating oil pressure readings on your gauge or warning light can indicate bearing clearances have opened up beyond spec, allowing oil to bypass the bearing surfaces faster than the pump can maintain pressure. Rhythmic metallic ticking or rattling from the timing cover area may signal a worn timing idler or tensioner bearing, especially on belt-driven DOHC engines after 60,000–90,000 miles or during a scheduled timing belt service. Copper or metallic debris in the oil or on the drain plug magnet during an oil change can indicate bearing material is shedding — a sign the overlay has worn through to the substrate layer. Rough idle or vibration that worsens