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Problems easily overlooked in diesel engine maintenance
First, only replace the plunger and nozzle, without considering the overall condition of the valve. When the oil valve becomes worn, the residual pressure in the high-pressure fuel line can become excessively high, causing the fuel nozzle to fail to shut off properly, leading to fuel dripping. This can result in excessive exhaust smoke, knocking in the cylinders, and unstable engine operation. To check the oil valve, use a pressure gauge ranging from 0 to 600 kg/cm². When the pressure drops from 200 kg to 180 kg/cm², the pressure should hold for more than 15 seconds. If not, the oil valve needs to be replaced. Alternatively, lift the high-pressure fuel pipe and pump diesel until the level is flush with the nozzle. Return the throttle to the stop position, then quickly turn the crankshaft half a revolution. If the fuel pipe doesn’t suck back, it’såˆæ ¼; otherwise, the oil valve should be replaced.
Second, only adjust the valve clearance and ignore the valve timing. Many people just follow the specified clearance but neglect checking the actual valve timing. Especially in older engines, wear on the camshaft can cause the valves to open earlier and close sooner, resulting in poor intake, incomplete exhaust, increased fuel consumption, and reduced power. When adjusting valve clearance on aged engines, it's advisable to slightly reduce the clearance to compensate for timing errors. For example, on an S195 diesel engine, reducing each valve clearance by 0.1 mm can shift the valve timing by about 3 degrees. However, the clearance should never go below 0.2 mm, as this could lead to improper closing due to thermal expansion. If the clearance is already at 0.2 mm and the timing error exceeds 5 degrees, the engine's performance will deteriorate significantly, and the camshaft should be replaced.
Third, only focus on the oil level in the sump and ignore the oil quality. Many people just top up the oil without ever checking its condition or replacing it. As we know, used oil contains a lot of oxidized substances and metal particles, which reduce its lubricating properties, increase component wear, and shorten the engine's lifespan. It's important to regularly check the oil quality. A simple way is to manually rub the oil between your fingers. If you feel mechanical impurities or if the viscosity is low, it should be replaced immediately. Another method is to drip some used oil onto a white paper. If the black spot is small and light in color with a yellow ring around it, the oil can still be used. But if the spot is large and dark with no yellow trace, it’s time to change the oil.
Fourth, only clean the air filter and ignore the possibility of air short-circuiting. There are many reasons for air short circuits, such as an improperly sealed air filter, missing gaskets at the intake pipe joints, or the intake pipe being inserted into a hose without proper clamping. Also, if the air filter lacks an apron or has damaged parts, unfiltered air can enter the cylinder, increasing wear on the piston, rings, valves, and other components.
Fifth, only clean the oil filter and neglect the oil chamber. Most diesel engines have hollow connecting rod journals with oil plugs at both ends, known as cleaning chambers. Under centrifugal force, the lubricating oil carries impurities to the chamber walls, improving lubrication quality. It's recommended to remove the oil plug every 500 hours of operation and clean the chamber and oil passages according to the manufacturer’s guidelines to maintain optimal engine performance.