Crankshaft bearings are the thin steel-backed shells lined with a soft bearing material — typically aluminium or copper-lead alloy — that separate the crankshaft journals from the block main bearing bores, relying on a pressurised oil film to prevent metal-to-metal contact at all times. A complete crankshaft bearing set covers the full complement of main and, on some applications, big-end journals required for a single engine rebuild. The failure mode that ends engine life most abruptly is bearing knock: a rhythmic, low-pitched hammering noise that rises with engine speed and deepens under load, caused by a bearing shell that has worn beyond its oil clearance or lost its backing due to oil starvation. Bearing wear accelerates dramatically when oil change intervals are extended or when the engine is regularly started and driven hard before oil has fully circulated. Because crankshaft journal dimensions and undersize grades vary between engine families and between service intervals, the OE part number is the definitive reference — using the wrong undersize will destroy the bearing within minutes of running. MAHLE and KOLBENSCHMIDT are two of the most respected names in OE bearing supply, manufacturing to original tolerances for the full range of Volkswagen Group, Toyota, and Ford engines.
Bearing sets are engine-specific: journal diameter, width, and oil hole position all differ, and engines requiring an undersize bearing — where journals have been reground during a previous rebuild — need a set matched to that specific undersize grade. The OE number on this page links to the standard (STD) specification for your engine. If the crankshaft has been reground, the undersize grade (0.25 mm, 0.50 mm, etc.) should be stamped on the journal or recorded in the engine's service history. Always confirm via engine code rather than model name, as power variants of the same engine often use different journal diameters.
OEM bearing shells from suppliers such as MAHLE or KOLBENSCHMIDT are produced to the exact overlay alloy composition and wall thickness specified by the engine designer. Quality aftermarket sets from established brands like IPSA or CLEVITE meet the same dimensional and metallurgical standards and are widely used in professional engine rebuilds. Budget shells with thinner overlay material or inferior backing steel will wear faster and may fail to maintain the oil film under high-load conditions, causing accelerated journal wear — an outcome that is considerably more expensive to correct than the initial bearing replacement.
If the engine is being dismantled for a full bottom-end rebuild, replacing main and big-end bearings as a set is standard practice, because both sets experience similar conditions and similar wear rates. Replacing main bearings alone while leaving heavily worn big-end shells in place is a common false economy. Some OE bearing sets are sold as main bearings only; others include both main and big-end shells in one kit. Check the part description carefully and, if in doubt, order both sets — the marginal additional cost at rebuild time is negligible compared with the labour of a second teardown.
The earliest audible sign is a deep, rhythmic knock from the lower engine that increases with rpm — distinct from the higher-pitched valve train noise further up the engine. This knocking typically softens briefly immediately after an oil change (fresh oil partially fills the increased clearance) before returning. Oil pressure may be noticeably lower than the manufacturer's specification at idle, and the oil warning light may flicker at low rpm. In advanced cases, metal particles are visible in the drained oil or on the magnetic sump plug. Any of these signs warrants immediate investigation to avoid catastrophic engine failure.
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