Crankshaft Deflection Measurement

Crankshaft used to transforms the linear motion of the pistons into a rotational motion that is transmitted to the load.Piston connected with crankshaft by connecting rod.Each units of the crankshaft supported by crank bearing(usually journal bearing) In multi-cylinder engine every units piston connected with crankshaft create rotational motion according to firing order.Crank shaft alignment is necessary for smooth engine operation.

Causes of Crankshaft Deflection

  • Crankshaft bearing wear
  • Lack of proper lubrication system
  • Improper crankshaft balancing
  • Improper bearing support
  • Torsional vibration
  • Engine vibration

 Deflection Measuring Instrument

Crankshaft deflection gauge(Analog): One complete rotation of the indicator indicate 1mm deflection.It contains 100 segments,so 0.01mm deflection can be measured.

Analog Deflection Gauge

Crankshaft deflection gauge(Digital): By it deflection can be measured more preciously than manual gauge.It can measure 0.001mm deflection.

Digital Deflection Gauge


Excessive deflection can causes crankshaft breakdown as well as main bearing and crank pin wear.After six months operation crankshaft deflection should be taken and keep  +/- 0.5mm tolerance limit.

Deformation gauge setting
Generally in every engine there is a punch mark for setting the gauge.Also it can be measured by following way

If D is the diameter of the main bearing shaft then the gauge will place at a distance D/2 from the center of the main shaft dia. See the picture.
Gauge Setting Pisition
Gauge Setting Position
Positions of Taking Reading :
Usually five position selected for measuring deflection.Right side,Left side,Bottom and two position near top(about 30 degree apart from vertical position)Positions are shown in the figure-A,B,C,D & E.
 “Usually bottom position reading is not taken due to chance of fouling by connecting rod” 
Five positions
Five positions
After dial gauge inserted between two crank waves.After setting the gauge the indicator is set to zero position at a point among five points.At other positions dial gauge indicator indicate positive and negative reading.

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