A crankshaft's twist is assessed by examining witness marks. Before installation, these marks are etched onto both the crankshaft journal and the mating crank web. The interference fit between these parts (approximately 1/570 to 1/600) creates a compressive load of about 77 MN/m². If the crankshaft experiences an extreme load (e.g., sudden engine stall, starting with a liquid-filled cylinder, or bottom-end bearing failure), the journal might slip on the web. Misalignment of the witness marks indicates the degree of twist.

Twisting typically occurs at the journal-to-web interface, especially under extreme loads or impacts.

• Engine stalling: A sudden stoppage at full speed, such as when the propeller is jammed during grounding.
• Hydraulic Lock: Attempting to start the engine with a cylinder full of liquid, leading to excessive pressure on the crankshaft.
• Bearing Failures: A bottom-end bearing failure can result in obstruction, causing stress and twisting at the crankpin.

The location and extent of twisting depend on the affected unit:

• If slippage occurs at the web closest to the timing wheel, all units are impacted.
• If it happens further along the crankshaft (e.g., near Unit 2), only the adjacent units (e.g., Unit 1 and Unit 2) may be affected.

Up to 5° of twist might be tolerable without correction. This is due to the overlap in the air start timing, although, fuel pump and exhaust valve timing will be slightly affected. Small slippages can be accommodated by hydraulically adjusting the camshaft to correct the timing. However, any slippage must be carefully monitored to ensure it doesn't increase.

If twisting is minor (≤5°):

• Adjust Camshaft Timing: Realign the camshaft hydraulically to restore proper fuel pump and exhaust valve timing.

If twisting is excessive (>5°):

Jacking the Crankshaft:

• Turn the engine until the affected web is horizontal.
• Place a wooden plank beneath the crankshaft and position a hydraulic jack between the web and the plank.
• Remove the main bearing cover and top shell of the affected journal.
• Cool the journal using dry ice and heat the web to expand it.
• After sufficient preparation, reassemble the main bearing shells (without shims) and tighten the bearing cover.
• Gradually increase the hydraulic jack pressure to rotate the web back into alignment.

Monitor the process carefully to avoid sudden movements where the web may overshoot the original witness marks. Overshooting indicates that the shrink fit is compromised, which necessitates crankshaft replacement.

If the twisting is irreparable, or if the shrink fit is damaged during the adjustment process, the crankshaft must be replaced.