I. Maintenance of the valve Train
Maintenance of valves and valve seats
Regularly check the valve sealing performance and promptly grind and repair any air leakage
Clean the carbon deposits on the valve heads and valve seats to prevent them from getting stuck on the valves
Check for wear, erosion and deformation of the valves. Replace the damaged parts immediately
2. Valve clearance Inspection and Adjustment (Core Focus)
Measure the valve clearance when the machine is cold and strictly follow the standard values of the equipment
Excessive clearance: Abnormal noise occurs, insufficient air intake, and poor exhaust
Too small clearance: The valves do not close tightly, are prone to erosion, and may even bend the valves
After long-term use, disassembly, assembly and maintenance, the clearance must be recalibrated
3. Maintenance of camshafts and tappets
Check for wear, pitting and spalling of the CAM profile. Replace it in time if the wear exceeds the standard
Observe whether there are any scratches or jamming on the surface of the tappets to ensure smooth movement
Change the lubricating oil on time to avoid dry grinding which aggravates component wear
4. Maintenance of timing transmission components (timing gears/belts/chains)
Check that the tooth surface of the timing gear is worn, chipped or loose, and the meshing clearance is normal
Timing chain/belt: Check for tightness, aging, cracks, and delamination. Replace it compulsion upon expiration
It is strictly prohibited to privately modify the timing phase to prevent confusion in the gas distribution sequence
5. Maintenance of valve springs
Check whether the spring is broken, fatigued or has lost its elasticity
If the springs are skewed, rusted or lack elasticity, replace them in pairs. Do not mix and use individual ones
Avoid the spring retaining ring from falling off and prevent the valve from falling into the cylinder
6. Maintenance of air ducts and valve guides
Replace the air filter element regularly to prevent dust from entering and causing abnormal wear of the valves and conduits
Check the valve guide clearance. If the clearance is too large, it is easy for engine oil to seep into the combustion chamber and blue smoke to come out
Clean the intake and exhaust pipes to ensure unobstructed air flow
II. Common Faults, Causes and Phenomena
Fault 1: Abnormal noise from the valve train
Fault phenomenon: A clear knocking sound and a dull knocking sound occur during operation
The main reasons are: Excessive valve clearance and noise caused by movement impact. The valve spring is broken and lacks sufficient elasticity. The camshaft and tappets are severely worn. The meshing clearance of the timing gear is too large and the tooth surface is damaged
Fault 2: Poor valve sealing and air leakage
Fault symptoms: Decreased power, unstable idle speed, low cylinder pressure, and difficult starting
The main reasons are: carbon deposits, erosion and wear on the valves and valve seats, and poor adhesion of the sealing surfaces. The valve clearance is too small, and the valves cannot close completely. The valve stem is bent and deformed, and the valve guide is stuck
Fault 3: Abnormal exhaust smoke
Fault symptoms: Black or blue smoke is emitted, and fuel consumption increases
The main reasons are: blocked air intake, insufficient valve opening, and incomplete fuel combustion (emitting black smoke). The valve guide is severely worn, causing engine oil to leak into the cylinder and catch fire (emitting blue smoke).
Fault 4: Disordered valve timing
Fault symptoms: Difficult to start, unstable speed, sudden drop in power, and in severe cases, unable to start
The main reasons are: elongation of the timing chain, slippage and breakage of the belt, and gear displacement. The timing marking during maintenance and assembly is correct
Fault 5: Valves are stuck or jammed
Fault symptoms: Single cylinder does not work, there is severe shaking, and even mechanical damage occurs
The main reason: Excessive carbon deposits get stuck on the valve stem. The valve guide is rusted and lacks oil for poor lubrication. The valve stem is deformed and its movement is obstructed
Fault 6: Valve spring failure
Fault symptoms: Slow valve return, idle vibration, insufficient high-speed power
The main reason: Long-term high temperature and fatigue use lead to the attenuation of elasticity.
The spring is rusted, broken and deformed.