I was working on a brand-new 75,000 dwt Panamax bulk carrier, equipped with a national production patent engine — the MAN B&W 6S60MC. After commissioning, the ship embarked on a one-year global round-trip voyage. For the first few months, everything ran smoothly. However, around 3,000 operating hours into the journey, a mechanical failure occurred.
At that time, the vessel was carrying nearly 70,000 tons of iron ore, en route to Peru. Suddenly, the main engine began producing a loud, rhythmic knocking sound. The engineers on duty immediately informed the bridge to reduce speed. Upon inspection, they located the noise coming from the fourth cylinder. Although the thermal parameters of the cylinder remained relatively stable, we decided to stop the engine for a more detailed check.
After opening the camshaft box of Cylinder 4, we discovered significant damage: there were five small pits, each about 1.5 cm², on the high-pressure pump head of the cylinder, and a 2 cm² pit near the left side of the fuel cam. Due to the tight schedule, we had to take temporary measures by sealing the cylinder to maintain partial power until we could reach the next port.
Referring to the technical drawings, the structure of the high-pressure pump is as follows:
[Image placeholder: Marine host high-pressure pump]
This type of high-pressure pump operates using a single-cam mechanism, where the fuel roller guide moves via a thrust block inside the cavity. A roller pin (D4) is installed, with its free end secured by a set screw (D12) to prevent axial movement. Because the roller device is subjected to constant vibration and impact, it's crucial to ensure the screws are not only tightened but also secured with anti-loosening measures such as lockwire, threadlocker, or riveting.
Upon further analysis, we determined that the root cause of the knocking was due to the loosening of the roller pin’s set screw. Under the continuous stress of vibration and impact, the pin gradually withdrew from its hole, allowing the pin axis to become free. This caused the roller guide to tilt, changing the contact from a surface-to-surface to a line-to-line contact, which significantly reduced the contact area and led to fatigue and eventual fragmentation under heavy load.
After inspecting the fourth cylinder’s high-pressure pump, the findings confirmed our diagnosis. The roller pin had loosened by approximately one-third of the thread. When the roller was removed, the pin slid out of the hole. To prevent similar issues in the remaining cylinders, we inspected all five other high-pressure pump units and found that their set screws were not properly secured. Using a hex key, they could be easily loosened, which posed a serious risk.
Since we didn’t have threadlocker on board, we implemented a temporary fix by tightening the set screws and riveting them at two or three points around the bolt. This ensured the screws wouldn’t loosen again. Later, a maintenance engineer from MAN-B&W in Brazil arrived to replace the fuel cam in Cylinder 4. He verified our inspection and confirmed that our actions were correct and necessary.
This incident highlighted the importance of proper maintenance and attention to detail, especially for components that are not typically subject to regular disassembly. The hidden nature of these parts makes them easy to overlook, yet their failure can lead to critical operational problems. Moreover, according to maritime safety standards, spare parts like roller guides or cams are not always required onboard, making it difficult to handle such failures at sea.
This experience taught me the value of proactive maintenance and thorough inspections. I hope this account helps raise awareness among my colleagues and serves as a useful reference for future operations.
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