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Problems easily overlooked in diesel engine maintenance
First, only replace the plunger and nozzle, ignoring the overall condition of the valve. When the oil valve wears out, the residual pressure in the high-pressure fuel line can become too high, causing the fuel nozzle to fail to close properly, leading to fuel dripping. This results in excessive exhaust smoke, knocking 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 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, pump diesel into it until the level is flush with the nozzle, return the throttle to the stop position, and quickly reverse the wheel half a turn. If the fuel pipe mouth doesn’t suck back, the valve is good; otherwise, it should be replaced.
Second, adjust only the valve clearance without checking the valve timing. Many people just follow the specified clearance but neglect the actual timing. Especially in older engines, wear on the camshaft can cause the valves to open early and close prematurely, leading to poor intake, incomplete exhaust, increased fuel consumption, and reduced power. When adjusting valve clearance on an aging engine, reduce the clearance slightly to compensate for timing errors. For example, on an S195 diesel engine, each valve clearance can be reduced by 0.1 mm, which shifts the valve timing by about 3 degrees. However, the clearance shouldn’t go below 0.2 mm, as this could cause the valve to not close tightly 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 significantly degrade, and the camshaft should be replaced.
Third, focus only on the oil level in the sump, ignoring the oil quality. Many people simply top up the oil without ever checking its condition or replacing it. Used oil contains a lot of oxidized substances and metal particles, which reduce lubrication efficiency and increase wear on engine components, shortening the engine's lifespan. Always check the oil quality regularly. A simple way is to rub the oil between your fingers—if there are mechanical impurities or if the viscosity is low, it should be replaced. Another method is to drip some used oil onto a white paper. If the 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, black, and has no yellow ring, it’s time to change the oil.
Fourth, clean only the air filter and ignore the possibility of air short-circuiting. Air short circuits can occur due to various reasons, 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. Other issues include broken intake hoses or missing air filter covers. These problems allow unfiltered air to enter the cylinder, increasing wear on the piston, rings, valves, and other internal parts.
Fifth, clean only the oil filter and neglect the oil chamber. Most diesel engines have hollow connecting rod journals with oil plugs at both ends, known as oil chambers. Under centrifugal force, the lubricating oil carries impurities that settle on the chamber walls, improving lubrication quality. It’s important to remove the oil plug every 500 operating hours and clean the chamber and oil passages according to the manufacturer’s instructions to maintain optimal engine performance.