Only topping up engine oil without replacementEngine oil consumption is low under normal conditions, yet it is easily contaminated and deteriorated, losing its protective effect on the diesel engine. In practical operation, most pump truck operators only monitor and replenish oil level, while neglecting oil quality inspection and replacement of degraded oil. Long-term oil topping-up without replacement will easily cause severe mechanical failures such as bearing bush burning and shaft seizing.
Direct installation of new cylinder liners and pistons without size matchingWhen replacing cylinder liners and pistons, many technicians mistakenly believe that all brand-new parts are standard and fully interchangeable for direct assembly. Mismatching a maximum-size cylinder liner with a minimum-size piston will result in excessive fitting clearance, insufficient compression pressure and difficult engine startup. During replacement, the size grouping codes of cylinder liners and pistons must be checked, and only parts with identical grouping codes can be assembled.
Failure to check plunger travel marginAfter adjusting the fuel supply advance angle, the plunger travel margin still needs to be inspected, as it is closely related to the wear of the plunger and barrel. When the plunger pair wears out, the plunger needs to travel upward for a longer distance to start fuel supply, which delays the fuel injection timing. Loosening the adjusting bolt or installing thicker adjusting shims will raise the lower limit position of the plunger and reduce its travel margin.
Inaccurate measurement of cylinder clearanceWhen measuring cylinder clearance, operators fail to measure at the position perpendicular to the piston pin hole on the piston skirt and take measurements at other directions instead. The piston skirt in the direction perpendicular to the piston pin hole suffers the most severe wear under lateral pressure, so the standard clearance measurement must be conducted at this exact position.
Heating pistons with open flamePistons and piston pins are precision fitted parts. Heat expansion is required during piston pin installation. Some maintenance personnel heat pistons directly with open flame, which is extremely improper. The correct method is to heat pistons evenly and slowly in hot oil. Direct open-flame heating is strictly prohibited.
Polishing bearing bushes with abrasive clothWhen replacing bearing bushes, some technicians polish bushes with abrasive cloth instead of manual scraping to increase the contact area with the crankshaft. This maintenance method is inadvisable. The abrasive grains on the cloth are hard, while the bearing bush alloy is soft. Grains will easily embed into the bush alloy during polishing, accelerating wear of crankshaft journals and greatly shortening the service life of the crankshaft.
Over-tightening of boltsStandard tightening torques for all bolts are clearly specified in the equipment manual and must not be altered arbitrarily. Many users assume tighter bolts mean higher safety, but over-tightening will cause bolt breakage, thread stripping and subsequent equipment malfunctions.
Excessively high tire pressureBoth excessively high and low tire pressure shorten tire service life and compromise driving safety, especially in summer. Scientific inflation standard: take the original factory standard pressure as the baseline and make slight adjustments according to ambient temperature.Tire pressure in summer should be 5% to 7% lower than that in winter due to thermal expansion of air at high temperatures. In winter, tire pressure shall reach the standard value or be slightly higher.
Sudden cold water addition when radiator boilsOverload operation, poor heat dissipation and insufficient coolant will cause the radiator to overheat and boil. Pouring cold water immediately at this time will result in thermal shock, cracking the cylinder head and cylinder block. Correct emergency procedure: stop operation at once and allow the diesel engine and coolant to cool down naturally.
Applying grease on cylinder head gasketApplying grease on the cylinder head gasket during assembly will cause part of the grease to burn inside the cylinder under high temperature after cylinder head bolts are fastened. Residual grease remains on the joint surface between cylinder block and cylinder head, creating sealing gaps. High-temperature and high-pressure gas will damage the gasket and cause air leakage. In addition, grease forms carbon deposits under continuous high temperature and accelerates aging and failure of the gasket.
