Some domestic forklifts are equipped with the C240PKJ diesel engine of ISUZU. Some users experience early wear when operating the machine less than 1000H. The reason is mainly due to improper use. Based on the experience, this article puts forward some measures to effectively extend its service life.
1. Early wear symptoms and causes
The main symptoms of early wear are: cylinder pressure drop before using 1000H; difficulty in cold start; severe blow-by gas in crankcase exhaust hole; black smoke from exhaust pipe during heavy load operation; significantly reduced power performance.
When disassembling, it was found that the piston ring was seriously worn, and the opening gap of the first air ring was about 2mm (use limit is 2mm); the cylinder liner appeared a step, and the maximum clearance at the top dead center was 0.18-0.29mm; from the top dead center down Within 25mm, the exterior has become discolored, the mechanical properties of the chromium plating layer on the interior surface have deteriorated, and there are traces of dry friction generated after the lubricant is drained.
The main reason for the failure is that the new machine failed to strictly implement the running-in and use requirements stipulated by the manufacturer at the initial stage of use of the new machine; low-temperature startup is frequent or frequent startup and sudden load after startup; improper use and maintenance.
2. Preventive measures for early wear
(1) Run-in should be performed according to technical requirements
The new machine generally goes through factory inspection and running-in to make it meet the technical requirements of the product. After the machine is installed, it must be further run-in. Generally, the run-in period is 2000-3000km or 50-100h, mainly to improve the quality of the friction surface of the auxiliary pair.
According to the part wear characteristic curve, the parts wear quickly during the running-in period of the machine. This is due to the relatively rough and uneven surface of the newly processed parts, which produces meshing wear. The peeled metal or oxide forms serious abrasive wear . Therefore, the new machine must be run-in according to certain technological procedures and technical requirements.
When driving the new engine, speed limit, load limit and oil change should be carried out according to the technical requirements, and pay attention to maintaining a good thermal state (cooling water temperature 80-90°C) and normal engine oil pressure. It is strictly forbidden to suddenly increase the throttle, which can greatly reduce the coordination The amount of wear on the friction surface increases the service life of the parts. Avoid and reduce early failures.
Judging from the wear results of cylinders, piston rings and other components, 2/3 is caused at the time of starting, that is, the amount of wear from the start to the time the lubricant enters the friction surface accounts for 2/3 of the total wear.
In low temperature operation, the lubricating oil is very thick, and it is difficult to enter the friction surfaces; due to poor lubrication, the lubricating oil drains between the friction surfaces to form dry friction, and the wear is particularly severe; the sulfur content in the fuel is high, and the anhydride in the fuel gas In many cases, when the cooling water temperature is low, acids will form on the cylinder wall, which will strongly etch the cylinder wall; the temperature of the piston is low, and the thermal expansion has not yet occurred, and the gap between the cylinder is also large. In the above case, the lateral movement of the piston is also increased, and the piston ring moves greatly in the groove. At this time, if the load is suddenly increased, the wear of each component will be increased.
(2) The machine should be used correctly
In the process of use, insist on warm-up start, cold shake slowly, idle speed heating, low speed start, maintain normal working water temperature and drive at medium speed.
(3) Maintenance of "three filters" should be strengthened
The air filter directly affects the service life of the engine. If the air filter has low filtration efficiency or poor quality, and the soft seal is not tightly connected, all kinds of dust will leak directly into the cylinder, thereby exacerbating the cylinder liner, piston ring and other machines. Pieces of wear. Practice has proved that if the air filter is not installed, the wear of the cylinder liner will increase by 8 bits, the wear of the piston ring will increase by 9 times, and the wear of the piston will increase by 3 times. Especially in the operation site of most forklifts, the concentration of industrial dust is tens or several milligrams per cubic meter. If the source of pollution is not strictly controlled or the air filter is not maintained in time, and the use of perforated, cracked and soft seals If the filter is not strict, the consequences will be more serious.
In a heavily polluted operation site, it is best to use two or more compound air filters connected in series to ensure the quality of the filtered air.
The maintenance of the oil filter is also very important. For forklifts operating in harsh environments, it is best to change the lubricant once every 2-3 months or after every 150 hours of work. When changing the lubricant, it is best to clean or replace the oil filter.
(4) Lubricant should be selected correctly
All relevant quality indicators should be comprehensively considered. For forklifts that often work under heavy-duty work load, frequent start and stop, and serious pollution around the environment, lubricating oils with slightly higher viscosity or less affected by temperature changes should be used. .
The lubricating oil grade used by the diesel engine should strictly implement the variety specified by the manufacturer. For the same model, if the conditions of use are different, the requirements for lubricants should also be different. Frequent cold starts or frequent starts, the higher the load and the larger the range of load change, the more advanced lubrication is required.
