A  Normal Conditions: The cylinder pressure rapidly increases and reaches the required uniform 

pressure value. 

B.  Piston Ring Fault: The first stroke pressure is low, increasing in the following strokes, but the 

pressure has not reached normal levels. Add engine oil in the cylinder, the pressure increased 
significantly. 

C.  Valve Fault: The first stroke pressure is low, and can not be increased in the following strokes. 

Add engine oil in the cylinder, the pressure is not increased. 

 

Test is completed. 

Next 

435

2.6.7.4 Engine Noise Diagnosis 

Engine vibration is actually referring to the engine resonance noise. When the engine's vibration 
frequency is the same as the vibration frequency of a fault, the noise will be perceived. Severe 
vibrating usually generates big noise, and it is generated by internal parts fracture or serious 
engine wear and tear. A slight vibration can be heard, but the sound is not big. Slight vibration is 
due to the engine internal components wear, loose or engine external components broken and it 
can lead to serious or slight vibration. In the engine noise diagnostic, the resonance noise cause 
must be found in order to eliminate the fault. 

1.  There is noise when engine has load. 

1 

Inspect whether the tension of the drive belt is too tight or strained? 

 

2 

Inspect the exhaust system. Whether the system is interfered with the other body 
components or scraping to ground? 

 

3 

Inspect the existence of the flywheel cracking, deformation and other components 
intervention. Is the flywheel normal? 

 

4 

Inspect whether the main bearing clearance is too large, and if it exceeds the specified 
value.  

Standard value (0 . 016 mm～0 . 034 mm)

 

 

Standard value (0 . 018mm～0 . 044mm) 

 

5 

Inspect connecting rod bearing clearance, and does it exceed the specified value?   

Yes 

Replace the flywheel assembly. Confirm whether 
the fault is fixed. 

No 

Yes 

Replace the connecting rod bearings.Confirm 
whether the fault is fixed. 

Next 

Yes 

Replace the main bearings. Confirm whether the 
fault is fixed. 

No 

Yes 

Relocate and install the exhaust system to confirm 
whether the fault is fixed. 

No 

Yes 

Replace/adjust the drive belt to the specified value, 
and confirm whether the fault is fixed. 

No 

436

6 

Confirm that the fault is fixed. 

2.  Engine shock lightly with warm up 

1 

Use fault diagnosis tester to read the "Knock" related to data. Is the engine knocking? 

 

2 

Inspect whether there is exhaust manifold leakage? 

 

3 

Inspect connecting rod bearing clearance, and does it exceed the specified value?   

Standard value (0 . 018mm～0 . 044mm)

 

 

4 

Confirm that the fault is fixed. 

3.  When it is in idle speed, or warm stage, engine has vibration. 

1 

Inspect drive belt tension. Is it too loose or worn? Any fault? 

 

2 

Inspect whether the viscosity of the engine lubrication oil is abnormal? 

 

3 

Inspect whether the generator and air-conditioning compressor is working properly. 
Any abnormal sound during working? 

Yes 

Refill engine lubrication oil suitable for the current season 
temperature, confirm whether the fault is fixed. 

No 

Yes 

If necessary, replace the drive belt. Confirm 
whether the fault is fixed. 

No 

Yes 

Replace the connecting rod bearings.Confirm 
whether the fault is fixed. 

Next 

Yes 

Replace the exhaust pipe pad and tighten the 
exhaust pipe again. 

No 

Yes 

Inspect the engine timing systems and fuel quality, 
repair the faulty part. 

No 

437

 

4 

Inspect the valve, valve spring and other valve components. Any fault? 

 

5 

Inspect the piston pin gap. Does it exceed the specified value?   

Standard value (0mm～0 . 006mm)

 

 

6 

Inspect whether the connecting rod is bent? 

 

7 

Inspect piston to cylinder gap value. Does it exceed the specified value?   

Standard value (0.0275mm～0 . 0575mm)

 

 

9 

Confirm that the fault is fixed. 

Yes 

Replace failed components, confirm whether the 
fault is fixed. 

Next 

Yes 

Replace failed components, confirm whether the 
fault is fixed. 

No 

Yes 

Replace failed components, confirm whether the 
fault is fixed. 

No 

Yes 

Replace failed components, confirm whether the 
fault is fixed. 

No 

Yes 

Replace failed components, confirm whether the 
fault is fixed. 

No 

438