How to Measure Crankshaft Deflection

Crankshaft Deflection:
Crankshaft deflection must be taken twice- before starting the d'carb and after completion of d'carb. This is done to ascertain whether the crankshaft journal is deviated from the theoretical axis or not. The deflection is recorded by using dial deflection gauge which is fitted between the webs of the crankshaft in each unit.

The complete shaft is then rotated in the direction of the operational rotation of the generator which may be a clock or anti-clockwise. The reading of the dial gauge is noted while turning the crankshaft which indicates opening and closing of the webs. Smaller the reading better is the crankshaft deflection.

Procedure:

With the running gear in place, the crank to be measured has to be turned towards (before or after) B.D.C until the dial gauge can be fitted next to the connecting rod at
the position indicated. Pre-tension the dial gauge slightly and set it to “0”. Turn the crankshaft with the turning gear, and record the dial gauge reading in the crank positions as shown in the figure. The difference between the indicated values at B.D.C. and T.D.C. shows the amount of crank deflection during one revolution. When measured values lie above the maximum permissible limits, the cause has to be found and the necessary remedial measures taken. (defective main bearing, engine
support altered due to hull deformation, loose holding-down bolts, defective shaft line bearings, etc.).