If a mechanical diesel engine fails during operation, it can lead to serious damage to its core components and potentially cause major machinery accidents. In most cases, before a failure occurs, the engine will display certain abnormal signs—such as changes in speed, unusual noises, irregular exhaust, elevated water temperature, or fluctuating oil pressure. These symptoms are key indicators of potential problems, and operators must be able to recognize them quickly and take immediate action to prevent catastrophic failures.
First, the "speed" issue.
(1) Warning signs: The engine suddenly accelerates uncontrollably, with a harsh and abnormal sound, and emits excessive blue or black smoke from the exhaust pipe. This is commonly referred to as "speed racing." It typically occurs at idle and not under load, often when the load is suddenly removed or reduced during start-up or operation. The main cause is a malfunction in the governor system, leading to uncontrolled fuel supply or excess oil in the sump. If not addressed immediately, this can result in severe damage such as blown cylinders or broken crankshafts.
(2) Emergency measures: The primary goal is to shut down the engine. You can do this by cutting off the fuel supply, pressing the brake, blocking the air intake, or releasing the high-pressure fuel line. Another option is to run the engine under heavy load while braking, which can force it to stall due to insufficient torque.
Second, cylinder sticking.
(1) Signs: The engine speed drops, it becomes difficult to operate, the sound is dull, and the water temperature rises above 100°C. If you spray water on the engine parts, it evaporates quickly. This usually happens due to a severe lack of coolant or a failure in the cooling system. If the engine stops abruptly, it may cause the piston to stick in the cylinder.
(2) Solutions: Let the engine idle for a while or turn off the crankshaft to help cool it down. Once the temperature drops to around 40°C, slowly add coolant. Do not add water immediately, as sudden temperature changes can cause cracks or deformation in engine components.
Third, cylinder knocking.
(1) Symptoms: A metallic "knocking" sound is heard from the crankcase, similar to a hammer tapping the floor. Oil pressure also drops. This is a serious mechanical failure caused by loose connecting rod bolts or stretched necks, leading to excessive clearance between the connecting rod and the crankshaft. If oil pressure remains normal, it may not be a knocking issue but could be related to incorrect fuel timing.
(2) Action: Immediately stop the engine and perform a full inspection. Replace any damaged parts to prevent further damage.
Fourth, bearing burnout.
(1) Indicators: The engine makes a dull, heavy noise, as if the load has suddenly increased. Speed decreases, oil pressure drops, and black smoke comes from the exhaust. This happens when the lubricating film on the bearing surface breaks down, causing metal-to-metal contact and rapid temperature rise, eventually leading to seizure.
(2) Response: Stop the engine immediately, remove the connecting rod and bearings, inspect the cause, and replace the damaged parts.
Fifth, broken crankshaft.
(1) Early signs: A dull, percussive sound comes from the crankcase. The knocking noise increases with throttle input. At idle, the engine vibrates heavily, and black smoke is emitted. A broken crankshaft is typically caused by fatigue at the neck shoulder, with gradual cracking over time. Initially, the signs may be subtle, but they become more noticeable as the crack expands. If the engine is running smoothly but the knocking frequency matches the throttle, it could be near the breaking point. Inspecting the flywheel manually can reveal excessive axial clearance, indicating a broken crankshaft.
(2) Steps: As soon as any of these signs appear, stop the engine and inspect the crankshaft. If damaged, replace it immediately to avoid total engine failure.
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