1. Working conditions of exhaust valve.

Eduction in ship diesel engine valve working conditions is very bad, the air valve base, direct contact with high temperature combustion products during the valve opening is under high temperature (900 ~ 1000 ° C) and corrosive gas high speed (600 m/s) flushing, valve core temperature as high as 700 ~ 800 ° C, in the middle of valve plate and valve stem transition arc temperature is 600 ~ 700 ° C, exhaust valve working temperature distribution as shown in figure 1-1.
Excessive temperature can reduce the mechanical properties of metal materials and heat deformation of materials.
When the valve seal is not tight, it will cause the high temperature gas to burn the valve surface.
Valve seat, valve and valve seat under the effect of inertia force and spring force, also bear the considerable impact of alternating load, beating in the valve or valve clearance increases, the load will be significantly increased.
The impact of valve and seat is easy to form a sealing surface deformation and serious wear.
For more than the vast majority of Marine diesel engine is turbocharged diesel engine, due to the stress of fresh air in the intake port to prevent oil from valve catheter may, therefore, prone to dry friction between metal.
However, there is a layer of lubricating oil such as lubricating oil or smoke oil between the air valve of the general diesel engine and the exhaust valve seat alloy surface of the supercharged diesel engine.
In addition, there will be wear and tear between the stem and the pipe, and the top of the stem will be impacted and worn by the rocker arm.
   

2. The influence of additional factors.

Because of rising fuel prices and fierce competition in the shipping market, shipowners use cheap, low-quality fuel to reduce costs to improve their competitiveness and gain more profits.
The fuel has a high viscosity, long period of combustion, and high content of vanadium, sodium and sulfur.
This kind of fuel combustion in diesel engines, the residue in the emissions (fuel ash) are only part of it with exhaust gas to leave machine, while the rest still remain in some high temperature in the engine (497?
On the parts of 797.
For example, the exhaust width and the piston top, formed deposition, resulting in the so-called "high temperature corrosion".
So far, there has been no economically rational process to remove corrosion elements from residual oil, and even high-grade alloy steels and surfacing steels are corroded by fuel.
In diesel engine running in violation of the provisions of car maintenance, low temperature start the diesel engine, low temperature force load, rapid changes in diesel engine cylinder combustion temperature, in the condition of diesel engine load, handle a sharp transformation, worsen diesel engine cylinder combustion condition, a lot of bad atomizing bulky heavy oil particles sprayed into the cylinder, causing severe after burning and not over a burning, serious carbon deposit to the surface of exhaust valve valve line is also to soot pollution, and even lead to host starting difficulty, this becomes the next host drive soon after oil and exhaust valve fault hidden trouble, so the manipulation and maintenance of the bad habit of diesel engine is also causing diesel engine valve fault factors.