How to troubleshoot the problem of the 320B excavator not starting?

A Caterpillar 320B excavator accidentally overturned beside the road during long-distance transportation. After the control machine was lifted by a crane, it was found that only the protective shell on the engine side of the excavator was damaged, while the rest of the parts remained intact. The driver's inspection revealed that the engine oil, diesel and cooling water had all been lost to varying degrees. After adding engine oil, diesel and water respectively and starting the engine, only a strong clashing sound between the starter and the engine flywheel could be heard. At the same time, it was observed that the engine fan blades only rotated slightly, and the fault remained when the engine was started again.

To find out "why the starter cannot drive the engine to rotate", first of all, it was checked whether the fault was in the electrical part or the electric motor part. When using a wrench to move the bolts back and forth on the engine crankshaft pulley, it feels very difficult and the pulley can only rotate a very small Angle back and forth. This indicates that the inability of the starter to drive the engine to rotate is caused by excessive engine resistance, not a fault in the electrical part. Analysis suggests that before the excavator is placed on a trailer for long-distance transportation, the technical condition of the engine is normal. Therefore, it is impossible for the timing system, connecting rod valve train, or crankshaft to be stuck. The failure of the starter to drive the engine to rotate occurs after the excavator overturns. When the excavator overturns, the position of cylinder I of the engine is higher than that of cylinder VI, and the oil pan is higher than the position of the cylinder head. Under such conditions, the engine oil in the oil pan will gradually flow into the combustion chamber through the gap in the cylinder wall. Since cylinder VI is at the lowest position and cylinder I is at the highest, the cylinder with the greatest possibility of engine oil flowing into the fuel chamber is Cylinder VI, followed by Cylinder V and Cylinder IV, while cylinder I has the least possibility. So, the valve covers of cylinders IV, V and VI were removed. A straight screwdriver was inserted into the gap between the intake and exhaust valves of cylinder VI. The purpose was to keep the intake and exhaust valves of cylinder VI open all the time. At this time, a wrench was used to turn the crankshaft pulley back and forth. It was felt that the rotation Angle of the crankshaft was slightly larger than before. Using the same method, keep the intake and exhaust valves of the V cylinder open. When turning the crankshaft pulley, you will feel that the crankshaft can rotate at a larger Angle. Keep the intake and exhaust valves of cylinder IV open. When the crankshaft pulley is turned, the crankshaft can rotate completely 360°.

This proves that it is the engine oil in the oil pan that flows into the combustion chamber through the gap in the cylinder wall. Due to the large amount of oil flowing into the combustion chamber, when the starter (or by using a wrench to turn the crankshaft pulley) rotates the crankshaft, the compression ratio is too high during the upward movement of the piston (all gaps are in a completely sealed state). The rotational resistance of the crankshaft is too large, thus showing that the starter cannot drive the engine to rotate. After identifying the cause of the malfunction, it was decided to insert a 1mm feeler gauge into the gaps between the intake and exhaust valves of cylinders IV, V, and VI instead of a flat-head screwdriver (as the flat-head screwdriver was too thick), to prevent the valves from pressing down too much and damaging the piston. However, during the test run, the starter still failed to start. Therefore, the thickness of the feeler gauge was increased from 1mm to 1.5mm. When the engine started again, it could start smoothly. And a large amount of engine oil was discharged from the exhaust pipe. At this moment, the feeler gauges of two cylinders slipped out from the valve clearance, and the engine was immediately blocked and shut down. Reinsert the feeler gauge, start the engine smoothly again, and let it idle for about 1 minute. However, after removing the feeler gauge from Cylinder IV, the engine stalled again, indicating that there was still a lot of oil in the combustion chamber. So, reinsert the feeler gauge, start the engine again, and let it idle for 5 minutes. After it was estimated that all the oil in the combustion chamber had been drained, successively remove the feeler gauges from cylinder IV and cylinder V. All the engines were running normally. Finally, the feeler gauge of Cylinder IV was pulled out, and the engine was also running normally. It indicates that the fault has been completely eliminated. The troubleshooting of this fault provides us with enlightenment: Similar faults are also common when using the Cummins engine installed on the TY220 bulldozer. That is, if the solenoid valve and check valve on the PT pump do not close tightly and diesel enters the combustion chamber, the starter cannot drive the engine to run.

At this point, simply rotate the crankshaft back and forth a few times, and the diesel will flow back to the oil pan from the gap in the cylinder wall, making it easier to start. If the engine oil, due to its excessive viscosity, enters the combustion chamber and is difficult to flow back to the oil pan from the cylinder wall gap within a short period of time, the engine will be hard to start. Therefore, when encountering new problems, it is essential to think of similar fault phenomena in order to quickly identify the cause of the fault and propose simple solutions.