Crankshaft deflection

Crankshaft deflection, or web deflection, is the change in the gap between adjacent crank webs as the crankshaft turns, measured with a dial gauge or electronic indicator set in the axial bore between the webs. The crank is rotated through bottom, two sides, and top, and the readings show whether the crankshaft is bent or the main bearings have worn unevenly, since a true straight shaft in line bearings reads near zero throughout. Readings are taken cold and sometimes hot. Limits are set by the engine maker, often around 1/10000 of the crank stroke, and an out-of-limit value signals bearing wear, a slack chock, or hull deformation before a crank crack develops.