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Maintenance knowledge



Q:Engine system-cooling system fault diagnosis


When excluding overheating fault, keep in mind that the oil sump is too full to increase the oil temperature and transfer to the coolant system of the oil cooler.

1)The function of the temperature sensor must be correct because any high temperature overheating will cause severe damage to the piston and cylinder liner.

2)Engine thermostat must operate correctly to ensure the engine to run at the optimum temperature range. Too hot or too cold will shorten the service life of the engine. The thermostat controls the temperature of the cooling liquid, when the temperature drops below the working temperature, the thermostat will be closed, then the cooling liquid will flow into the pump inlet from the bypass; when the cooling temperature rises to a certain extent, the two thermostats will open at the same time, the flow of coolant pipe began to be constrained; Under working temperature in the engine  the thermostat will be open and the bypass valve will be closed.

Note: If there is no thermostat, engine is not allowed to run. At this time, the coolant channel resistance is small so that the coolant is unrestricted and flows into the pump inlet from the bypass, which will cause overheating of the engine.

Q:Engine system- fuel system fault diagnosis


1.There is air in the fuel piping.

1)If there is air in the fuel piping, the engine will start difficultly, operate violently, lack of fire, power too low, and discharge smoke too much and cylinder burn out and keep knocking

2)A source of air into the fuel system is easily overlooked is between the oil tank and pre filter inlet pipe. At the top of a joint oil tank, the suction pipe extends to the tank bottom. If the position that the suction pipe and the pipe joint connected has cracks or pinholes, the air will come into the fuel system.

2.High pressure pump timing (requires turning tool)

1)Determine the top TDC of the cylinder (the TDC of the compression stroke) 

2)While turning the crankshaft slowly, push the timing pin into the bore of the camshaft gear. (Note: the crankshaft gear and camshaft gear are marked, but the camshaft gear and the oil pump gear are not marked).

Q:Basic requirements for repairing engines


  1. Clean, clean and clean;

 2.Regular accessories

3.Correct disassembly steps

4.Correct structural dimensions

5.Correct maintenance tools

6.Correct tightening torque

7.Correct testing

Q:Simple steps on fault diagnosis of engine on the vehicle


If the electrical fault occurs, we recommend that the vehicle be diagnosed and eliminated according to the following steps.

The first step: check the generator drive belt,  use hand in 1/2 of center of two wheels to apply 15 kg of pressure, pressing the belt 10-15MM lower is normal. If the belt is loose, it should be adjusted (Belt should be checked once in each two months). If the belt has been aging, slipping and crazing, it should be replaced.

The second step: check if the generator external wire connecting parts have broken wires, wrong connection, short-circuit phenomenon, and use voltmeter to measure B + point if there is battery voltage.

The third step: keep the key door in "open" position, but do not start the engine, with the voltage meter measuring if D point has voltage or not, and observe if the charging indicator light is bright.

The fourth step: start the generator with a voltmeter to measure the voltage of the generator. The voltage of B should achieve the following values: above 27V/13V (refer to 24V or 12V system, the same below), at the same time the voltage changes a little 0.1 ~ 0.2V.

The fifth step: open part of the load, such as car lights, measuring voltage: voltage should be more than 27V/13V, while adding and reducing the throttle, the voltage has moderate changes from 0.2 to 0.4V.

The sixth step: turn on the main appliances such as air conditioning, light and so on, measure voltage: the voltage should be above 27V/13V, while adding and reducing the throttle, the voltage has a greater degree of change from 0.5 to 1V.

In the fourth step, If the generator has no output of voltage, can take the following measures for inspection, use test lamp (a string wire 2W - 6W indicator) to connect across the generator main output end of B + and D + end excitation, observing indicator lights, if off, it means the generator is normal and the car excitation circuit has faults that needs to be checked out. From fourth step to sixth step, diagnose that the vehicle charging indicator line has breaking phenomena (usually the indicator is damaged, the dashboard connector is loose, the circuit is broken); if lights on, need to repair or replace the generator.

Tools: multi-meter / test lamp.

Q:Adjustment Of Clutch Separation Mechanism


If the free stroke is too long, the clutch will not be separated completely, the transmission shifting will be difficult. Meanwhile it will make friction plate and the pressure plate on the clutch be worn out faster result in reducing the service life of the clutch.

If the free stroke is too short, in severe case , the release lever and the inner end of the separation bearing surface will touch that equals to give a separating force to the inner end of release lever, which will make clutch slip at work and can't transfer power reliably; Meanwhile the wear between the driven plate and pressure plate is worse even burned out in severe case. What's more also the wear between separation bearing and separation of bearing wear and the inner end of the release lever will be faster. 

1.The clearance between the clutch master cylinder and the main pump piston is 0.5~1.0MM

A)Loosen the lock nut when adjusting.

B)Turn the push rod to the piston and stop when the putter hits the piston.

C)Back 1/3 ~ 2/3 button, tighten the lock nut.

D)The free clearance of the clutch pedal is 4 ~ 5MM after adjustment.

2.Adjust the spare part of the clutch shaft to ensure that the clearance between the separation and the separation of the bearing is 3 ~ 5MM.

A)Remove the clutch booster spring and push the pump piston to the bottom of the working cylinder.

B)Release the split pump push rod lock nut.

C)Turn the push rod in the opposite direction of the booster and stop when the resistance is felt (the separation bearings touches the separation fingers at this time).

D)Turn the push rod toward the booster to meet the technical requirements (generally 3 laps).

E)Tighten the lock nut after adjustment.

F)After adjustment, the free stroke of the clutch pedal is 30 ~ 60MM.

G)Install the split fork return spring.

Q:Precautions for bus use in winter


  1. Clean the battery, adjust the relative density of the electrolyte, and charge from outside the car.

The specific gravity of the battery electrolyte can show the condition of the battery. When the electrolyte temperature rises, the specific gravity will decrease, and when the temperature drops, the specific gravity will increase. When the battery is discharged, the specific gravity of electrolyte drops; when charging, the proportion of electrolyte rises. According to the determination of the electrolyte proportion determine the battery charging condition, safe charging battery electrolyte proportion is 1.280 (the electrolyte temperature is 15°C), if the electrolyte proportion is less than 1.2, the battery must be charged. In order to accurately compare the condition of the battery, the specific gravity at a certain temperature must be converted to the value of 15 °C standard temperature.

2.Check whether the coolant in the cooling system is suitable for local temperature conditions. The freezing point of the cooling liquid of the outdoor bus must be lower than the local extreme minimum temperature, or it should be replaced with the antifreeze which meets the requirements. The new vehicle usually is filled with water or antifreeze which is suitable for temperature conditions in the production area, so it must be checked. In addition, sometimes the vehicle will be filled with water or other brands of antifreeze when the liquid level drops, so it should also be checked.

3.After the vehicle is finished working every day, drain out the toilet water in the water storage tank and the windshield cleaning water tank to prevent from the volume expansion of water freezes that may damage containers and piping.

4.After the vehicle is finished working every day,  drain out the water in the storage tank, in case the brake system is frozen and cause accidents.

5.In order to prevent the temperature is too low to cause the engine water temperature is too low and slow heating, the radiator should be appropriate covered with shelter by reducing the intake air to reduce heat dissipation.

6.According to the performance of lubricating oil , change low viscosity winter lubricants for engine and chassis assemblies to reduce power loss and wear, depending on the performance of the lubricant.