Background: What Happened?
The vessel experienced a significant failure in the Aft stern tube bearing, which caused the engine to stall. When such a failure occurs, it is crucial to inspect all components in the kinematic chain, including the torsional vibration damper of the main engine. These dampers typically consist of a primary and secondary section, connected by steel leaf spring packs. These spring packs, along with pressurized engine oil, form chambers that help absorb vibrations.
The vessel in question was equipped with a Geislinger Monitoring System (GMS). However, since the engine was not running, a GMS report could not be issued. Thus, the only viable solution was a visual inspection of the damper.
Step-by-Step Damper Inspection Procedure
Before diving into the detailed process, it’s important to understand the critical nature of inspecting a damper in a 2-stroke engine after a major mechanical failure. This inspection ensures that any potential issues are identified and addressed before they escalate into more significant problems. Here, we outline the step-by-step procedure we followed to carry out a thorough damper inspection and restore the engine to optimal performance.
Removal of Covers
To begin, we removed the upper and lower covers of the damper. This step required disassembling the oil supply system and disconnecting both inner and outer sensors. Although straightforward, the challenge here was finding enough space to safely store the covers once removed. Afterward, the covers were secured to allow space for removing the side plate.
Removal of the Side Plate
Every damper design is different. In this case, we had to remove 38 bolts. It was crucial not to confuse four specific bolts with side plate bolts, as removing these could have caused internal damage to the damper. After removing the bolts, we installed a special lifting tool. The side plate weighs around 3.5 tons, so this tool is vital for safe handling. Once the tool was in place, the engine was rotated to position the tool for removal. Importantly, the engine was not rotated again until after the inspection, ensuring no further damage occurred.
The side plate was then secured using chain blocks, and we proceeded to remove it with the help of four specific bolts, which act as extractors. These bolts were tightened evenly to prevent misalignment.
Inspection of the Damper
After securing the side plate, the damper was inspected thoroughly. First, we removed the O-ring, which would be replaced later. The service engineer then examined critical areas, measuring important dimensions and checking for cracks in the springs.
Although no immediate faults were found, the service engineer discovered an important issue. The inner diameter of the cover, which slides on the inner star outer diameter, acts as a lubricated bushing. Due to a sudden vibration (likely caused by the Aft stern tube bearing failure), the bush rotated, blocking the lubrication tube. If left unaddressed, this could have led to overheating, damaging the entire damper.
The engineer recommended creating new lubrication tubes to resolve the issue.
Reassembly of the Side Plate
Once the inspection was complete, the side plate was carefully reassembled. We began by cleaning all surfaces, especially the groove for the new O-ring. The O-ring was then installed with a small amount of grease to keep it in place during reassembly. Although no special tool is required for side plate alignment, we used chain blocks to ensure precise positioning.
After the cover was aligned using two guide pins, we reinstalled the bolts. Every bolt was degreased, measured, and fitted with new shims and Loctite. The bolts were tightened in three stages:
- Hand tighten until the shim is immobile
- Tighten to 380Nm
- Tighten to 55 degrees, which equates to 4000Nm.
A special tool was required for the third stage, and afterward, each bolt was marked with a white permanent marker for rechecking.
Final Steps: Reinstalling the Covers
The last step was to reinstall the upper and lower covers. We cleaned and inspected all surfaces, including the oil supply system, and installed new O-rings. With everything securely in place, the damper inspection was complete.
Importance of GMS
The vessel is equipped with a Geislinger Monitoring System (GMS) MARK 5, which plays a critical role in monitoring engine health. Before the engine shut down, the system triggered several alarms, highlighting its ability to detect anomalies in real-time. This underscores the importance of having such an advanced system onboard, as it continuously tracks torsional vibrations and other key metrics, helping to prevent potential failures by alerting the crew to irregularities before they escalate into serious issues.
Importance of Regular Damper Inspection and Maintenance
For optimal engine performance, regular damper inspections and maintenance are essential. On 2-stroke engines, dampers must undergo service at specified intervals, which can sometimes be extended with the installation of a Geislinger Monitoring System (GMS). The GMS compares real-time measurements to initial calculations, providing a detailed assessment of the damper’s condition.
At INJEGOV, as an authorized GEISLINGER Sales & Service partner, we offer comprehensive damper maintenance, including the provision of an oil supply maintenance kit and TVC reports, which are accepted by the class as valid service documentation.
If you need expert damper maintenance services, feel free to contact us at technical@injegov.gr.
