If a mechanical diesel engine fails during operation, it can lead to serious damage to its core components and even cause major machinery accidents. In most cases, before the engine completely fails, there are usually some early warning signs such as changes in speed, unusual noises, abnormal exhaust, increased water temperature, or fluctuating oil pressure—these are known as the symptoms of a potential failure. Therefore, operators must be attentive and make timely, accurate judgments based on these signs and take immediate corrective actions to prevent catastrophic incidents.
First, the "speed surge" issue.
(1) Early signs: The engine suddenly accelerates rapidly without control from the throttle, making an unusual, harsh noise. It may emit thick blue or black smoke from the exhaust pipe.
(2) A "speed surge" typically occurs when the engine is idling and not under load. This usually happens when the load is suddenly removed or reduced during startup or operation. The primary cause is a malfunction in the governor system, which leads to uncontrolled fuel supply or excessive fuel in the sump. If not addressed immediately, this condition can result in severe damage such as cylinder blow-by or broken crankshafts.
(3) Emergency measures: The main goal is to shut down the engine quickly. Actions include cutting off the fuel supply by disengaging the accelerator and applying the brake, blocking the air intake to starve the engine of oxygen, releasing high-pressure fuel lines to stop fuel flow, or using heavy braking while the engine is still running to force it to stall due to insufficient torque.
Second, stuck piston (sticky cylinder) failure.
(1) Signs: The engine speed drops, it becomes difficult to operate, and a dull sound is heard. The water temperature gauge may rise above 100°C, and if you spray water on the engine parts, it evaporates quickly. This is often caused by a severe lack of coolant or a failure in the cooling system. If the engine stops at this point, it could lead to a stuck piston.
(2) Treatment: Allow the engine to 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. Avoid adding cold water immediately, as this can cause thermal shock and damage engine components.
Third, knocking cylinder failure.
(1) Early signs: A metallic "knocking" sound is heard from the crankcase, similar to a hammer hitting the floor. Oil pressure also drops. This type of failure is often caused by loose connecting rod bolts or stretched connecting rod necks, leading to excessive clearance between the bearing and journal. If the oil pressure remains normal, it may not be a knocking issue but rather a problem with the fuel injection timing.
(2) Treatment: Stop the engine immediately and perform a full inspection. Replace any damaged parts to avoid further damage.
Fourth, bearing failure (burned bearings).
(1) Signs: A dull, rhythmic noise is heard, as if the load has suddenly increased. The engine 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, leading to seizing and engine shutdown.
(2) Treatment: Shut down the engine immediately, remove the connecting rod and bearing, inspect the damage, and replace the faulty parts.
Fifth, broken crankshaft failure.
(1) Signs: A loud, percussive sound is heard inside the crankcase. As the throttle is applied, the knocking noise increases. At idle, the engine vibrates heavily, and black smoke is emitted. A broken crankshaft is usually the result of mechanical fatigue at the crankshaft fillet. Initially, the signs may be subtle, but as cracks grow, the symptoms become more pronounced. If the engine is operating at a certain throttle position and the knocking frequency matches, it may indicate that the crankshaft is about to break. To check, manually push the flywheel—if there's excessive axial play, it likely means the crankshaft is already broken.
(2) Treatment: If any of these signs are detected, the engine should be stopped immediately, inspected, and the crankshaft replaced if necessary.
By being aware of these common failures and their early signs, operators can significantly reduce the risk of major engine damage and ensure safer, more reliable operation.
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