Why deflections are taken
Crankshaft web deflection shows whether the shaft is bending between main bearings. Sag after a grounding, a worn bearing or a soft chock can open or close the webs. Readings are taken with a clock gauge between webs at top, bottom, port and starboard. The engine maker publishes a maximum allowed deflection.
How this calculator works
Vertical deflection = Top − Bottom. Horizontal deflection = Port − Starboard. Signs show the direction of sag. Compare the larger absolute value with the maker’s limit. Always use the official method in the engine manual, including the extra near-bottom reading if the connecting rod blocks true BDC.
Who should use it
Useful for engineers recording a deflection set. File the official sheet in the engine history.