A Shanghai W-100 excavator underwent an engine overhaul, and shortly after, the engine began to burn a significant amount of engine oil. According to the operator, the total oil consumption was around 25 kg over three shifts. This issue had not occurred prior to the overhaul, and the same operator confirmed that the same problem was not present before.
Following the overhaul, the pistons and piston rings were replaced. From a theoretical standpoint, it's unlikely for piston rings to break off during such a process. The machine showed no visible signs of damage, but there was indeed oil burning, evident from the dark smoke and strong oil smell. During inspection, when the first cylinder head was removed, carbon black residue was found on the top of the piston in the first cylinder, while the second cylinder showed no such signs.
Upon checking the intake tube, the technician observed a wet oil condition, suggesting that the oil was entering through the intake system. The remaining cylinders were not inspected further. Structurally, the W-100 excavator is equipped with a piston-type air pump, which is lubricated by the main engine oil. This oil flows back to the oil pan through the crankshaft and connecting rod system.
The air pump’s intake is connected to the engine’s air intake. So, how did the engine oil end up being burned? The operator explained that the air pump’s crankshaft connecting rod had been damaged, and during installation, some parts like the piston were not properly fitted. This allowed the airway to become interconnected. As the engine sucked in air, it also pulled in engine oil, which was then burned.
Before the overhaul, the compression ratio wasn’t sufficient to draw in the oil, so this issue didn’t occur. After the overhaul, the first cylinder started burning oil because it was closest to the upper part of the air pump’s intake, effectively acting as the "oil path." Since the air pump had stopped working, a temporary plug was installed to block its intake, resolving the issue. The machine returned to normal operation afterward.
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