If a mechanical diesel engine experiences a malfunction during operation, critical components can be damaged, potentially leading to serious machinery accidents. Normally, before a failure occurs, the engine will display certain abnormal signs in aspects such as speed, sound, exhaust, water temperature, and oil pressure—these are the symptoms of the impending failure. Therefore, operators must quickly and accurately identify these signs and take immediate action to prevent accidents.
First, the "speed" fault.
(1) Early warning signs: The engine speed suddenly increases rapidly and becomes uncontrollable by the throttle. The sound becomes unusual, harsh, and the exhaust pipe emits a lot of blue or black smoke.
(2) "Speed racing" occurs when the engine idles at high speed but doesn’t happen under load. It typically occurs when the load is suddenly removed or reduced during startup or operation. The main cause is a failure in the governor system, leading to uncontrolled fuel supply or excessive oil in the sump. If not addressed immediately, this can result in major accidents like cylinder blow-by or broken crankshaft.
Treatment measures include: First, cutting off the fuel supply by stopping the accelerator and applying the brake. Second, blocking the intake pipe to cut off air. Third, quickly releasing the high-pressure fuel line to stop fuel delivery. Fourth, using the engine's own braking system while operating under heavy load to force it to shut down due to insufficient torque.
Second, stuck cylinder failure.
(1) Early warning signs: The engine speed drops, it cannot operate properly, the sound becomes dull, and the water temperature rises significantly. A water temperature gauge exceeding 100°C is a clear sign. At this point, if you spray water on the parts, it evaporates quickly. This is usually caused by severe water shortage or a failure in the cooling system. If the engine stops suddenly, it may lead to a stuck cylinder.
(2) Treatment measures: Allow the engine to idle for a while or turn off the crankshaft to help cool down. Reduce the water temperature to around 40°C before slowly adding coolant. Avoid adding cold water immediately, as this could cause parts to warp or crack due to sudden temperature changes.
Third, faulty cylinder.
(1) Early warning signs: A "clicking" sound is heard from the crankcase, similar to a small hammer tapping the floor, commonly known as knocking. Oil pressure also drops. A faulty cylinder is a destructive mechanical issue, often caused by loose connecting rod bolts or stretched necks, resulting in excessive clearance between the connecting rod and journal. If knocking occurs but oil pressure remains normal, it may not be a case of cylinder knock, and the fuel timing angle should be checked instead.
(2) Treatment measures: Immediately stop the engine and perform a full overhaul, replacing any damaged parts.
Fourth, bearing failure.
(1) Early warning signs: A dull, heavy sound is heard, as if the load has suddenly increased. The engine speed decreases, oil pressure drops, and black smoke comes from the exhaust. Bearing failure occurs when the lubricant film on the bearing surface is damaged, causing direct metal contact between the bearing and the journal. This leads to rapid temperature rise and surface adhesion.
(2) Treatment measures: Stop the engine immediately, remove the connecting rod and bearing, inspect the cause, and repair or replace the damaged components.
Fifth, broken crankshaft failure.
(1) Early warning signs: A dull, percussive sound is heard inside the crankcase. The knocking noise becomes more noticeable when the throttle is applied. At idle speed, the machine vibrates heavily, and black smoke is emitted from the exhaust. A broken crankshaft is typically caused by mechanical fatigue at the crankshaft neck. Initially, the signs may be subtle, but as cracks develop, the symptoms become more apparent. When the crack reaches a critical point, the engine may experience loud knocking or vibration. To check, inspect the cover and manually push the flywheel. If there is significant axial play, it indicates that the crankshaft is broken.
(2) Treatment measures: If any of these signs are observed, stop the engine immediately and replace the crankshaft as soon as possible.
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