If a mechanical diesel engine experiences a malfunction during operation, it can lead to severe damage to its core components and even cause major machinery accidents. In most cases, before a failure occurs, the engine will exhibit certain abnormal signs—such as changes in speed, unusual noises, irregular exhaust, elevated water temperature, or fluctuating oil pressure. These symptoms serve as early indicators of potential problems. Therefore, operators must be attentive, quickly identify these signs, and take immediate, appropriate actions to prevent serious incidents.
First, the "speed" issue.
(1) Early warning signs: The engine speed suddenly increases rapidly and becomes uncontrollable by the throttle. The sound may become harsh or unusual, and the exhaust pipe may emit large amounts of blue or black smoke.
(2) "Speed racing" typically occurs when the engine is idling but not under load. It often happens when the load is suddenly removed or reduced during startup or operation. This condition is usually caused by a failure in the governor system, leading to uncontrolled fuel supply or excessive oil in the sump. If not addressed immediately, it can result in catastrophic failures like cylinder blow-by or crankshaft breakage.
Treatment measures include cutting off fuel or air supply. Emergency steps include: first, stopping the fuel flow by disengaging the accelerator and applying the brake; second, blocking the intake to cut off air; third, releasing high-pressure fuel lines to stop fuel delivery; and fourth, using heavy loads while braking to force the engine to shut down due to insufficient torque.
Second, sticking cylinder failure.
(1) Early warning signs: A drop in engine speed, difficulty in operation, dull sounds, and an increase in water temperature. The temperature gauge may exceed 100°C. At this point, if you spray water on the engine parts, it will evaporate quickly. This is usually due to severe water shortage or failure of the cooling system. If the engine is stopped immediately, it may lead to a stuck piston.
(2) Treatment involves running the engine at idle for a while or turning off the crankshaft to allow cooling. Once the water temperature drops to around 40°C, coolant should be added gradually. Avoid adding cold water directly, as it could cause thermal shock and damage engine components.
Third, faulty cylinder.
(1) Early warning signs: A "clicking" sound from the crankcase, similar to a small hammer hitting the floor, commonly referred to as "knocking." There is also a drop in oil pressure. This type of failure is often caused by loose connecting rod bolts, stretched necks, or excessive clearance between the connecting rod and journal. If knocking is present but oil pressure is normal, it may be due to incorrect fuel timing rather than a mechanical failure.
(2) Immediate shutdown and repair are necessary, with replacement of damaged parts.
Fourth, bearing failure.
(1) Early warning signs: A dull, heavy sound, as if the load has suddenly increased, along with a drop in speed, oil pressure, and black smoke from the exhaust. When bearings fail, the lubricating film is destroyed, causing metal-to-metal contact, rapid temperature rise, and eventual seizure of the bearing and journal.
(2) Immediate shutdown is required. The connecting rod and bearing should be removed, inspected, and repaired or replaced.
Fifth, broken shaft failure.
(1) Early warning signs: A dull, percussive noise inside the crankcase. As the throttle is applied, the knocking sound becomes more noticeable. At idle, the machine may vibrate heavily, and black smoke may appear from the exhaust. Crankshaft breakage is typically caused by mechanical fatigue at the neck shoulder. Initially, the signs may be subtle, but as cracks grow, the symptoms become more apparent. If the knocking frequency matches the throttle, it may indicate a critical stage of fracture. Inspecting the flywheel manually can help detect axial movement, which suggests a broken crankshaft.
(2) Upon noticing any signs, the engine should be shut down immediately, and the crankshaft should be replaced as soon as possible.
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