• If a Planned Maintenance System (PMS) is in use onboard, the running hours of the engine components are typically the primary factor in deciding when to open up a cylinder unit. The overhaul is scheduled based on the predetermined intervals specified by the manufacturer or the PMS.
• Significant reduction in compression pressure and peak pressure, as evidenced by the indicator card diagram, indicates that the cylinder unit's performance has degraded.
• If there is a crack in the liner or cylinder head, then the cylinder unit is immediately inspected and repaired.
• If the wear exceeds the maximum allowable limit, the cylinder unit must be opened up for overhaul
• If there is excessive blow past between piston rings and liner, the cylinder unit should be opened up
• Practical factors such as the ship’s location, available time in port, and whether immobilization is permitted can influence the decision to open the cylinder unit for overhaul
• After a scavenge fire, it is essential to open the cylinder unit to inspect for any damage and conduct an overhaul if necessary.
• A badly leaking cylinder liner O-ring is a clear sign that the cylinder unit needs to be opened for O-ring renewal or repair
• Excessive iron content in the scavenge drain oil analysis suggests excessive wear in the cylinder unit.
• If a broken piston ring is discovered during a scavenge space inspection, the cylinder unit must be opened up and the issue addressed.

Factors for deciding whether to renew or re-use piston rings:

• If a PMS is in place, piston rings are typically renewed after predetermined running hours, regardless of condition.
• Piston rings should be renewed if their wear rates suggest they cannot be safely used until the next scheduled maintenance.
• If a piston ring is found stuck in its groove or shows uneven wear (more on one side), it must be renewed.
• For chromium-plated piston rings, renewal is necessary if the chrome layer is worn out.
• If the axial clearance or radial clearance is excessive, renewal is necessary
• Visible damage such as scuffing, micro-seizure, excessive stretching, or a burnt appearance indicates that the piston rings need to be renewed.

Piston Rings can be reused if:

• Piston rings may be reused if the axial and radial clearance is within limits
• If the wear rate suggests the rings can be safely used until the next scheduled maintenance, they can be reused.
• Rings that can move freely in their grooves without any signs of sticking or jamming can be reused.
• If the piston rings show no marks of seizure, scratches, burnout, or any other form of damage, they can be considered for reuse.