If a main engine piston seizes in its liner at sea and replacement is impossible, the engine must be modified to allow the vessel to limp to port. The primary action is to remove the connecting rod of the affected cylinder, effectively isolating the seized unit. This process varies depending on the piston's position:

Scenario 1: Piston seized at Top Dead Centre (TDC)

This is the more favourable scenario. The procedure involves:

• The lower half of the bottom end bearing is secured using a chain block to prevent it from falling into the crankcase during disassembly.
• The hydraulic nut securing the lower half of the bottom end bearing is opened, and the bearing is carefully removed from the crankcase.
• The connecting rod is then secured using a chain block.
• The crosshead is locked in position on the crosshead guide using a dedicated locking tool.
• The crosshead bearing cap nut is opened.
• With the engine carefully turned using the turning gear, the connecting rod is slowly lowered and removed from the crankcase. This controlled movement is very important to prevent damage.

Scenario 2: Piston seized between TDC and Bottom Dead Centre (BDC) or at BDC

In this less favourable situation, removing the connecting rod without damaging components is unlikely. The connecting rod will need to be severed (cut). The piston itself will remain in the cylinder liner.

Post-Connecting Rod Removal (Both Scenarios):

Regardless of the piston's position, once the connecting rod is removed (or severed), the following steps are taken to isolate the affected cylinder and allow continued operation (following the maker's recommendation):

• The fuel pump for the affected cylinder is disabled by bypassing its cam roller, preventing fuel injection into the disabled cylinder. In the case of an Electronic engine, set the fuel index to Zero (0) from the MOP computer.
• The exhaust valve is deactivated by lifting its roller off the camshaft using a specialised lifting tool. With the Electronic engine, Disable the exhaust valve operation in the MOP computer. This prevents exhaust gases from escaping into the system from the disabled cylinder, although the cylinder will likely be vented in some other way.
• The starting air pipe to the cylinder is disconnected and blanked off at the main control air valve, preventing accidental air ingress.
• The lubricating oil supply to the crosshead of the affected cylinder is blanked off to prevent pressure drop of oil.
• The cylinder lubricator for the affected unit is set to "zero" delivery to prevent further lubrication of a seized and immobile piston.

Engine Operation under Reduced Load:

With the affected cylinder isolated, the engine can be operated at a significantly reduced load. The manufacturer's recommendations for operating under these special conditions must be strictly followed. Continuous monitoring of all engine parameters—temperature, pressure, vibration, etc. is important. Exceeding the manufacturer's specified load limits could cause further damage and potentially endanger the vessel.

The vessel proceeds to port under reduced speed and power, with the understanding that engine performance is compromised and that unforeseen issues may arise. Regular checks and careful monitoring are carried out until the damage is repaired at the next port.