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 machine operator, the total oil consumption was around 25 kg over three shifts. This issue had not occurred before the overhaul. The same operator confirmed that the problem wasn't due to any operator error.
Following the overhaul, the pistons and piston rings in the cylinder liners were replaced. From a theoretical standpoint, it's highly unlikely that the piston rings would break off and cause such issues. There were no visible signs of mechanical damage on the engine, but the smoke coming from the exhaust showed carbon black, and there was a strong smell of burning oil.
During the inspection, when the first cylinder head was removed, carbon black deposits were found on the top of the piston in the first cylinder, while the second cylinder showed no such signs. Upon opening the intake tube, the presence of wet oil was observed, suggesting that the oil was entering through the intake system. The other cylinders were not checked again.
From a structural perspective, the W-100 excavator is equipped with a piston-type air pump. The crankshaft, connecting rods, and piston components are lubricated by the main engine oil, which then flows back into the oil pan. The air pump’s intake is connected directly to the engine's inlet. So how did the engine oil end up being burned?
The operator later discovered that the air pump's crankshaft connecting rod had been damaged, and during the overhaul, some parts like the piston used for gas compression were not properly installed. As a result, the airway became connected, allowing engine oil to be drawn into the engine along with the air. Before the overhaul, the compression ratio was insufficient, so the engine couldn’t suck in the oil. After the overhaul, the first cylinder experienced oil burning because it was closest to the air pump’s intake port — essentially acting as the "oil passage." The oil burned first in this cylinder.
Since the air pump had stopped working, a temporary plug was inserted to block the air pump’s intake. Once this was done, the malfunction was resolved, and the excavator returned to normal operation.
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