At present, some operators and repair technicians have obtained a driver's license or a junior repairman certificate, but they still lack sufficient knowledge about mechanical construction principles and maintenance practices. It is common for them to use fasteners improperly during repairs—such as tightening them with excessive force or not at all. As a result, diesel engines often experience frequent malfunctions, and in some cases, serious accidents can occur. To raise awareness among most operators and repair personnel, the following precautions for installing key fasteners on diesel engines are outlined.
1. **Cylinder Head Nut**: When tightening the cylinder head nut, it should be done gradually in stages according to the specified torque. The tightening should follow a diagonal pattern, starting from the center and moving outward. When removing the cylinder head, loosen the nuts in the reverse order. If tightened unevenly, the cylinder head may warp or deform. Over-tightening can stretch the bolts, damage the threads, or even break the bolt. Under-tightening may cause leaks, oil seepage, or even burn out the gasket due to high-temperature gases.
2. **Flywheel Nut**: On engines like the S195 diesel engine, the flywheel and crankshaft are connected via a conical surface and a flat key. During installation, the flywheel nut must be tightened and secured with a thrust washer. Failure to do so can result in knocking sounds, damage to the crankshaft taper, or even breaking of the keyway, leading to severe accidents. Also, the thrust washer should only be folded once.
3. **Connecting Rod Bolts**: These bolts, made from high-quality steel, endure significant impact forces and should never be replaced with regular bolts. They must be tightened evenly, with both bolts tightened to the specified torque in several steps, and finally secured with galvanized wire. Over-tightening can cause deformation or breakage, leading to internal engine failure. Under-tightening can increase bearing clearance, causing knocking, increased load, and potential damage to the crankshaft.
4. **Main Bearing Bolts**: Proper installation of the main bearings is crucial. For a four-cylinder engine with full support, the five main bearings should be tightened evenly in a specific sequence: first middle, then second, third, fourth, and fifth. Each tightening should be followed by checking the crankshaft rotation. Incorrect torque can lead to damage similar to that caused by improper connecting rod bolt tightening.
5. **Balance Block Bolts**: These bolts should be tightened step by step to the specified torque. If not properly installed, the balance block may fail, leading to imbalance and vibration.
6. **Rocker Seat Nut**: Regular checks are essential. A loose rocker nut increases valve clearance, delays valve opening, and advances closing, reducing air intake and increasing fuel consumption. It also leads to incomplete exhaust and reduced engine power.
7. **Injector Lock Nut**: When installing the injector, the lock nut must be tightened to the correct torque, preferably in multiple steps rather than once. Over-tightening can deform the nut and cause the needle valve to stick, while under-tightening may lead to oil leakage, reduced injection pressure, and poor atomization, increasing fuel consumption.
8. **Fuel Valve Tight Seat**: When installing the fuel injection valve, ensure the seat is tightened to the specified torque. Too much tightness can cause the plunger sleeve to deform, while too little may result in oil leakage and poor fuel delivery, affecting engine performance.
9. **Injector Platen Nut**: When installing the injector assembly, ensure the pressure plate is correctly placed, and the steel pad thickness is appropriate. The platen nut must be tightened to the correct torque. Over-tightening can deform the valve body, while under-tightening may cause air leaks and difficulty starting the engine.
In addition, when installing the pump slide rotor and high-pressure oil pipe joints on the distribution pump casing, the spring should also be tightened according to the specified torque. Proper fastener installation is essential for the safe and efficient operation of diesel engines.
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