Thrust Bearing
A specialized bearing in the engine block that controls the axial (forward and backward) movement of the crankshaft.
A thrust bearing is a specialized type of plain journal bearing located in the engine block, designed to control the axial (fore-and-aft) movement of the crankshaft. While main bearings support the crankshaft rotationally, the thrust bearing features flange faces that ride against machined shoulders on the crankshaft webs, preventing it from sliding along its axis under load.
Axial load is applied to the crankshaft whenever the clutch is depressed in a manual transmission vehicle, or when the torque converter ballooning occurs in an automatic. This load pushes the crankshaft forward, and the thrust bearing absorbs this force. If the thrust bearing wears out, the crankshaft will develop excessive endplay, allowing it to slide back and forth. This ruins the crankshaft positioning, damages the connecting rods, and can cause the crankshaft position sensor to lose its signal.
Symptoms of a worn thrust bearing include low engine oil pressure, metal shavings in the oil pan, clutch engagement issues, and engine knocking. Endplay is diagnosed by placing a dial indicator on the crankshaft pulley and prying the shaft forward and backward. Worn thrust bearings require a complete engine tear-down and crankshaft machining or replacement.