Troubleshooting examples of T160A Bulldozer

1. Cannot start

Phenomenon: After normal use, the machine stops and cannot be restarted, and no smoke is emitted.

Diagnosis: The starter is working normally. It is initially judged that the fault lies in the oil circuit. When pumping oil with a manual pump, the amount of oil pumped out is sufficient and there is no air in the oil flow. Manual pumps can also work quickly. It indicates that the fuel supply is normal, there is no blockage in the fuel line, and there is no air leakage. As the machine was newly purchased not long ago, the possibility of the fuel injection pump (with the lead seal not removed) malfunctioning is relatively small. After reviewing the maintenance manual, it was found that the engine stop lever was controlled by an electromagnetic valve. Observing the engine stop lever, it seemed that it was not in the normal position. After manually pulling it, it started normally. It was determined that the fault lay in the solenoid valve. After replacing the solenoid valve, the engine worked normally and the fault was eliminated.

2. Difficulty in starting

Phenomenon: The machine stops after normal use, starts poorly, and the smoke exhaust volume is not large.

Diagnosis: When pumping oil with a manual pump, the amount of oil pumped out is not large, but there is no air in the oil flow. When the manual pump works rapidly, the vacuum degree generated is very high, and the pump oil piston will be automatically sucked back. It is determined that there is no air leakage in the oil circuit, which is caused by impurities blocking the oil circuit. The causes of oil passage blockage are as follows: ① The rubber layer on the inner wall of the rubber oil pipe detels or falls off, resulting in oil passage blockage. As the machine has not been in use for a long time, the possibility of aging is relatively small, so it is temporarily ruled out. If the fuel tank is not cleaned for a long time or unclean diesel is used, impurities inside will be sucked into the fuel line and accumulate in the narrow parts of the fuel line or in the filter, causing the fuel line to be blocked. After inquiring with the operator, it was learned that due to the tight supply of diesel in the second half of the year, diesel from non-official channels had been used for a period of time, and the diesel filter element had never been cleaned. It is suspected that the malfunction lies here. Remove the filter element. It's quite dirty. Replace the filter element. At the same time, check the oil passage to ensure it is unobstructed. The test run still failed to start normally. Rule out this possibility. ③ Wax or "water" clogs the oil passage. Because it was winter, I suspected that the fault was here. After inquiry, I learned that O# diesel was used and the oil-water separator had never been drained of water. As no wax was found blocking the oil circuit during the inspection just now, I judged that the fault was caused by "water". When I loosened the water drain plug, the water did not flow smoothly. After removing the oil-water separator, I found ice chips inside. After clearing them, it worked normally and the fault was eliminated.

3 Electrical appliance malfunction

Phenomenon: After working the night shift, the machine cannot start and the starter motor fails to rotate.

Diagnosis: ① Battery fault. The starter motor failed to rotate. It might be a problem with the battery. The terminal voltage of the battery was measured to be less than 20V (for a 24V battery). It was determined that the battery was faulty. After sulfation removal and charging, it returned to normal. ② Loose wiring. After using it for a period of time, the malfunction still persisted. The battery returned to normal after being sent for repair. At this point, the author thought for a moment. Since the battery was new, the possibility of it being discharged so easily was relatively small. So, the engine was started. It was found that the ammeter was shaking left and right, and the generator did not have a stable voltage output. At this time, there were two possibilities: one was that there was a fault in the excitation circuit, and the other was that the generator itself could not work normally. Upon inspection of the wiring, several loose parts were found. After tightening, the generator returned to normal. ③ Excessive load. After using it for a period of time, the battery was discharged again. The same fault occurred so many times that it couldn't help but draw the author's attention. After asking the driver, it was learned that this machine often works night shifts and the front and rear headlights often burn out. Generally, construction machinery adopts a single-wire system (negative terminal grounding), with the advantages of a simple circuit and easy maintenance. The drawback is that it is prone to burning out electrical equipment. So the front and rear headlights were changed to a dual-wire system, the malfunction was resolved, and the front and rear headlights rarely burned out.

The steering is not sensitive

Phenomenon: The right turn is not sensitive. After the joystick moves, sometimes it can turn, and sometimes the response is slow.

Diagnosis: Refer to the figure on the next page: This steering hydraulic system mainly consists of a coarse filter 1, a steering pump 2, a steering fine filter 3, a steering control valve 7, a brake booster 9, a safety valve and an oil cooler 5. The hydraulic oil in the steering clutch housing passes through the magnetic coarse filter 1, is sucked in by the steering pump 2, and then is pumped into the steering fine filter 3, enters the steering control valve 4, the brake booster and the safety valve. The hydraulic oil released through the safety valve (with a set pressure of 2MPa) flows into the bypass valve of the oil cooler. If the oil pressure in the bypass valve of the oil cooler exceeds the set pressure by 1.2 MPa due to reasons such as blockage of the oil cooler 5 or the lubrication system, the hydraulic oil should be drained into the steering clutch housing. When the steering lever is pulled halfway, the hydraulic oil flowing to the steering control valve 7 flows into the steering clutch. When the steering lever is pulled to the bottom, the hydraulic oil not only continues to flow into the steering clutch to disengage it, but also simultaneously flows into the brake booster, causing the brake to perform braking.

After analysis, it is initially inferred that the fault is caused by: ① The steering clutch cannot be completely disengaged or slips; ② The steering brake is not working. For 1, the reasons for the clutch not disengaging completely or slipping are as follows: The external factor is insufficient oil pressure for operating the steering clutch. The pressure measured at ports B and C is not much different. This is because only the right turn of this machine is not sensitive, while the left turn is normal. This indicates that the oil pressure is sufficient and the fault cannot occur here. The internal cause is a malfunction in the internal structure of the clutch. For internal causes, we need to conduct a disassembly inspection, which is rather complicated and will not be checked for the time being. For 2, there are three reasons why the steering brake does not function: ① Insufficient brake fluid pressure. The pressures at ports D and E were measured to be the same, so this possibility can be ruled out. ② The friction plates are slipping. As the machine has not been in use for a long time, the possibility of the friction plates wearing out is relatively small. ③ The braking stroke is too large. Tighten it with a torque of 90N·m and turn it back by 11/6 turns. The problem of unresponsive right steering was solved after the test run. At the same time, the possibility of a malfunction in the internal structure of the clutch has also been ruled out. The problem lies in the excessive braking stroke.