Crankshaft deflections are measured by using deflection gauge.
The deflection gauge is a dial gauge, which measures the distance between the adjacent webs spread at different angular positions of the shaft.
The dial gauge shows the distance up to which the stylus move when it is pressed.
Fit the dial gauge between the punch marks of adjacent webs, opposite to crankpin. Ensure that it is at half of the diameter from shaft centre to press the stylus 3 mm.
The clockwise rotation of the needle indicates closing of the webs.
The Corresponding gauge reading is taken as negative value.
Anticlockwise rotation indicates opening of the webs. The corresponding gates reading is taken as positive value.
Take the first measurement when the engine is at 30 degree after the bottom dead centre position.
Keep the gauge close to the side of the connecting rod.
Set the gauge to zero at this position.
Rotate the engine by turning gear.
Stop at each quarter and take the gauge reading using a mirror with flexible handle.
Take the final reading near bottom dead centre. The connection rod he is now at a position opposite to the first reading.
Take the average of the first and last reading to get the approximate bottom position.
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