Forged Crankshaft:

• Forged crankshafts have a continuous grain flow throughout the shaft, providing greater material strength and reduced susceptibility to cracks or failures under high stress.
• Being a single-piece construction, there is no shrink fit, eliminating the risk of slippage.
• Forged crankshafts have better resistance to fatigue and reduced stress concentration due to their uniform structure and absence of assembly joints.
• These crankshafts are smaller and lighter, which is advantageous for compact designs and weight-sensitive applications.
• Primarily used in smaller engines where space and weight considerations are critical.

Built-Up Crankshaft:

Fully Built-Up Crankshaft:

• Comprised of separately forged webs, crankpins, and journals, assembled using a shrink-fit method.
• Grain flow is not continuous, leading to comparatively lower strength.
• Higher stress concentration due to assembly joints.
• The advantage is it is simpler construction and allows for easier replacement of parts.

Semi-Built-Up Crankshaft:

• Crank throws are forged as a single piece with continuous grain flow, enhancing material strength.
• Better fatigue resistance compared to fully built-up crankshafts.
• Features larger pin diameters and lighter, smaller webs, reducing overall shaft weight.

Welded Crankshaft:

• Half-journal, webs, and crankpins are forged together and welded to similar sections.
• Welding and continuous grain flow enhance material strength.
• Post-welding stress relief minimizes residual stresses.
• Absence of shrink fits eliminates slippage risks, allowing thinner webs for a compact and lightweight design.

• Stop the engine and engage the turning gear.
• Start measuring deflections from the unit farthest to flywheel
• Place the crank pin at the point of 30° (position ‘B’) past the bottom dead centre.
• Install the deflection gauge in the pop point provided for this purpose.
• Set the reading on the gauge to 0 (zero reading) at the position ‘B’ in the figure.
• Slowly conduct turning of the engine in the normal direction of rotation, and measure the reading on the scale when the crankshaft is at the angle of ‘B’, ‘C’, ‘D’, ‘E’ and ‘A’ respectively, of which data shall be recorded.

Calculating deflection (d): Calculate the deflection values as based not the measured values and in accordance with the following formula and record the calculated values.

Vertical (V) deflection: dV = D - A+B/ 2

Horizontal (H) deflection: dH = C - E

positive/ negative deflection: open downward (+), closing downward (-) A, B, C, D and E represent the measured values respective at each corresponding position shown in the figure above.

1. Draw a horizontal reference line below the crankshaft.
2. For every unit, draw a vertical line representing the vertical deflection measurement for this unit.
3. Draw a soft curve using the points obtained by the measurements.
4. Finally, draw a baseline (tangent) to this curve to see which units deviate the most from the deflection curve.

This allows us to assess whether there are additional misalignments between the webs, even though the deflection values are within the manufacturer’s limits.