I was working on a brand-new 75,000 dwt Panamax bulk carrier, equipped with a national production patent engine—MAN B&W 6S60MC. After commissioning, the ship embarked on a one-year global voyage. For the first few months, everything ran smoothly. However, around 3,000 operating hours later, a mechanical failure occurred.
At that time, the vessel was carrying nearly 70,000 tons of iron ore, en route from Peru to another destination. Suddenly, the main engine began producing heavy, rhythmic knocking sounds. The engineers on duty immediately alerted the bridge to reduce speed and then listened carefully to locate the source. They identified the noise coming from the fourth cylinder, but thermal parameters showed no significant changes. After stopping the engine for further inspection, we opened the camshaft box of cylinder 4 and discovered damage: there were five 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 surface.
Due to tight schedules, we had to take temporary measures by sealing the cylinder to maintain partial power. During the voyage, the structure of the high-pressure pump is shown in the following figure, based on related drawings and materials:
[Image placeholder: Marine host high-pressure pump]
This type of main engine high-pressure pump uses a single-cam mechanism, where the roller guide device moves by swinging the thrust block inside the fuel roller guide cavity. The roller is mounted on a pin (D4), and the free end of the pin is secured with a set screw (D12) to prevent axial movement during operation. Given the frequent impact and vibration, the installation of these screws requires special attention—not only tightening them properly, but also applying anti-loose measures such as lock wire, threadlocker, or riveting. These steps are essential to prevent loosening over time and ensure safe and reliable operation.
Upon analyzing the failure, it became clear that the root cause was the loosening of the roller pin under continuous impact and vibration. As a result, the pin withdrew from its hole, allowing the pin axis to become free. This caused the roller guide to tilt forward and backward, changing the contact between the roller and the cam from a surface-to-surface contact to a line contact. This significantly reduced the contact area, leading to increased stress and eventual material fatigue and fragmentation.
After arriving at the port, we inspected the fourth cylinder’s high-pressure pump and confirmed our findings. The roller pin had loosened by approximately one-third of the thread. When the roller device was removed, the pin slid out of the hole. To prevent similar issues in the other cylinders, we checked all remaining five high-pressure pump units and found that their pins were not properly secured. Without threadlocker on board, we tightened the stop screws and riveted them in place at two or three points to prevent future loosening.
Later, a MAN-B&W maintenance engineer from Brazil arrived to assist in replacing the fuel cam of cylinder 4. He verified our inspection and the corrective actions taken, confirming that they were entirely correct.
This incident taught me a valuable lesson. The roller guide and fuel cam are not typically considered wear parts and are rarely disassembled under normal conditions. Their hidden nature makes it easy to overlook the importance of securing the screws properly. Moreover, according to maritime safety regulations, there is no mandatory requirement to carry spare parts like roller guides or cams. In the event of such an accident, the ship can face serious operational challenges and risks to safety.
I hope this experience serves as a useful reference for my colleagues and helps prevent similar incidents in the future.
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