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Caterpillar 3512B Type-Diesel Engine difficult to start what is the reason

Description of the phenomenon of mechanical failure

Beginning CAT-3512B diesel engine speed is slow start (starting motor feeling of weakness), over time, more serious difficulty in starting the last engine starting motor can not be driven to rotate.


CAT-3512B diesel engine starts working principle of the hydraulic system as shown in the drawings, the main by the hydraulic pump

1. Relief

2. Valve

3 main starter motor

4. Vice starter motor

5. Valve (6.7) and other components.

Chassis engine PTO the power transmitted to the hydraulic pump 1. Relief valve 2 would limit the system pressure to 23MPa or less. The engine is started, the oil valve 3 is turned so that the pressure of the oil pump driven by the main motor 4 starting rotation, you can start the CAT-3512B diesel engine. The starting system is also equipped with five vice starter motor, ball (6.7) is used to switch the primary and secondary starter motor 4 to start the motor 5.

CAT-3512B diesel engine start hydraulic system diagram

The CAT-3512B main and auxiliary starter motor coaxially mounted, the front axle with a drive pinion. The pinion with engine flywheel ring gear, thus boosting the engine rotation. Start the motor and the drive pinion friction plate installed between the one-way clutch, the clutch can be engaged automatically when the engine starts, starts automatically separated.


Analysts believe that the failure may be due to low pressure hydraulic systems, hydraulic pump damage, starting motor damage, and one-way clutch slip.

First, the pressure gauge connected to the hydraulic system, the START condition is detected the system pressure of only 3 MPa. Adjust the pressure relief valve 2 is limited to the system pressure is still 3 MPa, engine still does not start.

Secondly, the rotating ball (6,7), the main switch to start the motor four deputy to start the motor 5, the detection system pressure is only 12 MPa. Diesel can barely started at this time, but a small amount of smoke coming out the exhaust pipe.

Again, the disintegration of the hydraulic pump, the results found no abnormal wear.

Then, open the main and auxiliary starter motor rear cover and check the valve plate, no abnormal wear.

Finally, remove all of the starter motor, the clutch apart and found a large number of housing mashed copper scrap, copper clutch friction plate severe wear. Replace the main and auxiliary starter motor assembly after the test machine, the engine starts smoothly, start time is only 5 s, the pressure gauge shows the system startup is 20 MPa, the fault disappears.

Cause Analysis

Analysts believe that this failure is caused by the one-way clutch slip. As lining wear is a gradual process, with the friction plate wear, so that the gap between the friction plate increases, gradually slipping clutch serious engine can not be started until the last.


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