The valve mechanism’s primary duty is to control the exchange of gas in the cylinder, to open and close the valve on time, and to ensure that the valve does not leak. If the valve train isn’t working properly, the diesel engine’s power will reduce and it will be difficult to start. The following is a study of common diesel engine valve train defects, with an emphasis on prevention during work.
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Too Large or Too Small Valve Clearance
When the valve is closed, the valve lash is the distance between the end of the valve stem and the rocker arm head. The operation of a diesel engine is greatly influenced by valve clearance that is either too large or too narrow. The valve will not close tightly if the clearance is too tiny, resulting in air leakage or a burnt valve. As a result, the valve clearance must be checked and adjusted on a regular basis while in use.
Valve clearance sizes vary by model, with most diesel engines’ exhaust valve clearance being 0.05-0.1 mm larger than the intake valve clearance. Furthermore, the valve clearance varies depending on whether the car is cold or warm, and it is around 0.05 mm higher when the car is cold than when it is warm. The valve clearance we’re discussing is often the cold vehicle valve clearance. The intake valve on the S195 diesel engine, for example, measures 0.30 to 0.45 mm.
Wrong Gas Distribution Phase
The valve phase of the engine refers to the angle of the crankshaft as the intake and exhaust valves open and close. The valves open earlier and close later to allow more fresh air into the cylinders and to remove the exhaust fumes. Early opening refers to when the intake valve is opened 10° to 30° before the top dead center, while late closing refers to when it is closed 40° to 70° after the bottom dead center. The exhaust valve opens 40 to 60 degrees before the bottom dead center and shuts 10 to 30 degrees after the top dead center. Valve overlap occurs when both the intake and exhaust valves open at the same time.
Due to the inertia of the airflow, it is unable to alter its respective flow directions in a short period of time, and no exhaust gas will flow back to the intake pipe, nor will fresh air be expelled with the exhaust gas. The intake of fresh air and the entire discharge of exhaust gas are both affected when the diesel engine is out of phase. The valve phase will be wrong, the power will be diminished, the flywheel will not be able to rotate, the valve top piston, even the valve push rod, will be bent, the valve top will be broken, and the body will be cracked if the gear mark is incorrect or incorrect during assembling. If the gas distribution phase is incorrect, the gear mark should be checked immediately and corrected if necessary.
A broken valve can result in a variety of mechanical problems, ranging from minor damage to entire machine scrapping, as well as physical injuries. It is critical to avoid breaking the valve during the test or use procedure, especially in engines with valve repair.
The following are the causes of valve failure:
(1) The valve has failed due to poor workmanship.
(2) When the car is cold, the accelerator is used to increase the temperature and acceleration of the lubricant, which easily causes the valve spring to break, causing the valve to fall into the cylinder due to the driver’s improper operation.
(3) The engine’s valve phase is improper, the valve’s angle of early opening or late closing is incorrect, and the piston collides with and breaks the valve.
(4) Individual cylinder valve clearance or decompression adjustment is incorrect (multi-cylinder machines), and the valve is shattered owing to impact.
(5) The valve protrusion is too large or the valve sinking degree is insufficient, causing the piston to collide with the valve and break.
(6) If the protruding surface of one end of the valve rocker arm deviates to one side from the contact point of the valve rod end, the valve rod will be biased to the rocker arm seat or run in the other direction when the rocker’s arm descends lower, increasing valve guide wear. The valve will eventually break if it is not repaired in a timely manner.