6. Polish the bearing bush with emery cloth
For some inexperienced repairmen, scraping is a difficult job. Since the scraping technique is difficult to master, it is difficult for the bearings to meet the technical requirements. For this reason, when some people replace the bearing bush, in order to increase the contact area between the bearing bush and the crankshaft, they use emery cloth to polish it instead of scraping the bush. This method is extremely undesirable in actual maintenance, because the abrasive grains on the emery cloth are relatively hard, while the bearing alloy is soft. In this way, the sand grains are easily embedded in the alloy during grinding, and the wear of the journal will be accelerated when the diesel engine is working. Shorten the service life of the crankshaft.
7. Bolts are tightened too much
During the disassembly and assembly process of engineering machinery, bolts in many parts have specified torque requirements, such as transmission boxes, cylinder heads, wheel hubs, connecting rods and front axles. The tightening torques are specifically specified in the instructions. Do not Feel free to change it. However, many users mistakenly believe that tightening it will be safer, but tightening it too tight will cause the screws or bolts to break, and may also cause failure due to thread slippage.
8. Tire pressure is too high
The tire inflation pressure of wheeled construction machinery is an important factor in determining its service life and work efficiency. Tire pressure that is too high or too low will affect its service life and is not conducive to safe driving, especially in hot summer. The scientific inflation standard should be: based on the standard tire pressure, the tire pressure should be slightly adjusted as the temperature changes. For example: summer should be 5%-7% lower than winter, because the temperature in summer is high, the gas is heated, and the pressure increases. On the contrary, in winter, the standard air pressure must be reached or slightly lower.
9. Failure to check plunger stroke allowance
During the commissioning of the plunger fuel injection pump, many maintenance personnel do not pay attention to checking the stroke allowance of the plunger. The so-called stroke allowance of the plunger refers to the amount of movement that the plunger can continue to move upward after being pushed to the top dead center by the cam on the camshaft. After adjusting the oil supply start time, the reason why you need to check the stroke margin is because the stroke margin of the plunger is related to the wear of the plunger and sleeve. After the plunger and sleeve are worn, the plunger has to move upward for a while before it can start oil supply, thus delaying the start of oil supply. When the adjusting bolts are unscrewed or thicker adjusting pads or gaskets are used, the lowest position of the plunger moves upward, reducing the stroke margin of the plunger. Therefore, when repairing and debugging the fuel injection pump, you should first check this stroke margin to determine whether the fuel injection pump still allows adjustment. During inspection, the following different methods should be used according to the different structures of the fuel injection pump:
a) Rotate the camshaft, push the plunger to the top dead center, remove the oil outlet valve and valve seat, and measure with a depth vernier.
b) After the plunger is pushed to the top dead center, use a screwdriver to pry up the spring seat of the plunger spring to raise the plunger to the highest point.
Then insert a thickness gauge between the lower plane of the plunger and the tappet adjustment bolt to measure. The standard stroke margin of the plunger is approximately 1.5mm, and the ultimate stroke margin after wear should be no less than 0.5mm.
10. Boil the water tank and add cold water.
Overloading of the engine, poor heat dissipation or lack of water in the water tank will cause the water tank to boil. If cold water is added immediately at this time, the cylinder head and cylinder block will burst. Therefore, once the water tank is found to be boiling during use, emergency measures should be taken to stop the operation and allow the diesel engine cooling water to cool down on its own.