Five Mechanical Failures of Diesel Forklifts

Mechanical failures during the operation of a diesel engine may, at best, cause damage to base components, and at worst, lead to mechanical accidents. Before a diesel engine fails, certain abnormal signs will appear in its speed, sound, exhaust, water temperature, oil pressure, and other aspects, which are the precursor characteristics of the fault. Therefore, operators should quickly make accurate judgments based on the characteristics of the precursors and take timely measures to avoid accidents. 1. "Runaway" fault Precursor characteristics The speed suddenly increases and becomes faster and faster, beyond the control of the throttle; the sound is abnormal and piercing; a large amount of blue or black smoke comes out of the exhaust pipe. "Runaway" is overspeed idling and will not occur when working under load. It can only occur when the engine has just started or when the load suddenly disappears or decreases during operation. The main cause is a fault in the governor system, which causes fuel supply to lose control, or it is triggered by excessive oil in the oil pan. When the precursor of "runaway" occurs, if emergency measures are not taken immediately, it will eventually lead to major accidents such as cylinder knocking and shaft breakage. Handling measures The main purpose is to shut down the engine by cutting off fuel or air. Emergency measures that can be taken include: first, close the throttle to stop fuel supply and depress the brake; second, block the intake pipe to cut off air entry; third, quickly loosen the high-pressure fuel pipe to stop fuel supply; fourth, for vehicle diesel engines during travel, use a high-grade heavy load (braking) so that the engine stalls due to insufficient torque. 2. Cylinder seizure fault Precursor characteristics The speed decreases, operation is weak, the sound is dull, and the water temperature is extremely high. If equipped with a water temperature gauge, its indication exceeds 100 degrees Celsius. At this time, sprinkling some water on the components will cause rapid evaporation. The main cause is severe water shortage and failure of the water cooling system. If the engine is immediately shut down, cylinder seizure may occur. Handling measures Run at idle for a period of time or shut down and turn the crankshaft by hand to assist cooling, so that the water temperature drops to about 40 degrees Celsius, and then slowly add cooling water. Note that cooling water should not be added immediately, otherwise the components may deform or crack because the local temperature drops too quickly. 3. Cylinder knocking fault Precursor characteristics There is a "clicking" sound in the crankcase area, like the sound of a small hammer lightly tapping a hard floor, commonly known as "cylinder knocking." The oil pressure decreases, and it is more obvious during rapid acceleration. Cylinder knocking is a relatively destructive mechanical fault, mainly caused by loosening or withdrawal of connecting rod bolts or bolt stretching and necking, or by excessive clearance in the connecting rod shaft fit, resulting in bolts loosening or breaking. If there is a cylinder knocking sound but the oil pressure is normal, then it is not a precursor to cylinder knocking and should be considered from the perspective of adjusting the fuel supply advance angle. Handling measures Stop the machine immediately for inspection and repair, and replace with new parts. 4. Bearing burning fault Precursor characteristics The sound is dull, as if the load suddenly increases and the speed decreases, the oil pressure drops, and black smoke comes from the exhaust. Bearing burning will cause the bearing shell and journal to seize and stall the engine. The main cause is that the lubricating oil film on the bearing shell surface is destroyed, and the metal on the bearing shell and journal surfaces comes into direct contact, causing friction temperature to rise rapidly and resulting in adhesion. Handling measures Stop the machine immediately, remove the cover and inspect the connecting rod and bearing shell, identify the cause, and repair or replace. 5. Shaft breakage fault Precursor characteristics A dull knocking sound occurs in the crankcase, and the knocking sound becomes louder when the throttle is increased. At idle, the components tremble severely, and black smoke comes from the exhaust. Shaft breakage is caused by mechanical fatigue at the shoulder of the crankshaft journal and always has a gradual process from cracking to breaking. When the crack is hidden, the precursor characteristics are not obvious. As the crack expands, the precursor characteristics become increasingly obvious, eventually leading to shaft breakage and engine stall. If the throttle trembles or the knocking frequency matches and the machine is stopped, it may be at the critical point of shaft breakage. At this time, remove the cover for inspection and push the flywheel by hand. If the axial clearance is large and pushing is not laborious, it indicates that the crankshaft has broken. Handling measures Stop the machine immediately for inspection upon discovering the precursor, and replace the crankshaft promptly if a crack is found.