1. Main maintenance technology for valve and seat.

Before servicing, measure the distance between the bottom of the valve and the head of the cylinder.
If the difference is too large, it will affect the compression ratio of the diesel engine and the impact of the air valve on the piston, so the valve seat cushion must be replaced.

During maintenance, the following measures should be taken for the air valve after the long work: the roundness error and the cylindric error after the stem wear, the error can be obtained by measuring the micrometer of the outer diameter.
The replacement should be scrapped when these two errors exceed the limit of the gap between the catheter and the catheter.
The radial runout of the cylinder should not be greater than 0.003mm for the inspiration cone.
Otherwise, the replacement should be scrapped.
Check the valve when the top in the spindle of the lathe between head and tail thimble, two plunger cap at the top of the valve to the original processing pinhole, will dial indicator on the apron, and make the table contact contact with the air valve cone.
During the rotation of the valve, the maximum value of the reading change of the dial is the radial pulse.
At this time the air valve's clamping state is as shown in the figure above;
Check the air valve for cracks, pits and pits.
The outer surface of the stem is allowed to have 10 lines with a length of no more than 20mm, and magnetic inspection and demagnetising should be carried out on the conical surface and the stem coupling lock.
The cracked ones should be scrapped.

(1) welding process of valve and valve seat.

The exhaust valve and seat taken off from the main engine have a lot of grease, pitting pits, ablative and even burning, and must be cleaned.
Cleanup on the lathe machining off the surface dirt and original spray welding layer (layer thickness can be from the process of spray welding layer and base color is different, or car is iron sheet and roll silk judgment).
The spray welding layer is hard, the iron filings are small, and the female is mostly filamentous.
For the local ablative site, the dirt is worn by grinding wheel, and after the stain is not cracked, it can be resoldered.
Electrode can choose high cr-ni austenitic stainless steel welding rod, molybdenum effect will be better some, generally need to 200 ° C before welding, preheating of 1.
More than 5 hours, to small current, multilayer welding, pay attention to the interlayer between the tao and temperature at about 200 ° C.
It is used to grind out the parts that are higher than the base body.
  

(2) grinding process of valve and seat.

The grinding Angle of valve disc and seat must be adjusted and measured strictly according to the instruction manual.
Adjustments must be carefully especially stem sealing surface grinding Angle, using the dial gauge to look timing before grinding, should make the dial gauge for parts, contact area, circumference of a circle to find are calibrated to the grinding wheel in contact with the sealing face all, ordered its maximum deviation should be 0.
Within 05mm, this number is also the largest number of wear.
The grinding standard is that the grinding wheel must be evenly rubbed off the material from the broadband and the circumference of the entire sealing surface.
Clean the stem first when inspecting the wear layer of the stem;
Measuring the outer diameter of the stem in the circumference of the valve and the low limit specified in the specification;
Check the reticular cracks of the chromium plating layer, and there is a slight crack in the chrome layer on the valve head, but the coating is not allowed to be dermal.
After grinding, seal inspection should be carried out: the air valve cone shall be drawn with soft pencil to draw the lines, and the seat will be attached to the valve, and then it will be removed after 1/3 week.
If each pencil line is found to be erased from the same position in the middle, the seal is good.
In addition, the air valve device can be assembled according to the regulations, and the gas is poured into the kerosene. After 10 minutes of observation, if the valve does not leak the oil mark, it can also indicate that the seal is good.
 

2. Other defects and treatment.

(1) the valve breaks.

The main reason for the rupture of the valve is that the thermal stress is too large due to uneven temperature distribution on the valve, or the valve disc (seat) warping, which makes it bear a large bending stress.
Therefore, in the use of maintenance, it is necessary to strictly ensure that the valve stem and the catheter should be combined with the gap, and the abnormal wear should replace the catheter in time.
Because the excessive clearance can lead to poor heat dissipation, resulting in the leakage of the valve stem, the air leakage of the exhaust valve stem is more likely to cause the skid to die;
The excessive clearance also aggravates the transverse vibration of the valve, which increases the slip volume of the disc and the seat sealing surface and increases the wear and tear.
It may also cause the valve to take a single seat, which often causes the disc to break at the round corner of the stem.
Of course, the gap between the pipe and the stem should not be too small, otherwise it will cause the valve card resistance.
When assembling, the stem is in the catheter if it can be reduced slowly.
After long working wear, push the stem from the side with the hand, shake and loosen the feeling, but the judgment has exceeded the wear limit.
  

(2) detection and treatment of valve spring defects.

Attention should be paid to inspection of spring surface cracks, rust and other defects.
There are cracks, scrap.
Rust spots apply emery cloth to smooth and clean to avoid stress concentration.
The test of the platform on the spring, found bending and distortion, should be replaced.
The air valve is short of elasticity, which can cause the valve to close and cause leakage.
Air valve mechanism transmission parts out of contact, producing percussion, leading to increased wear.
Serious accidents may result in the loss of spring locking device.
In the maintenance, the standard spring should be compared with the relative deformation, which should be scrapped.
 

3, knot theory

Exhaust valve is an important part of diesel engine, and its working performance directly affects the normal operation of the main engine.
Therefore, the engineer must pay great attention to the exhaust valve work.

The following points are required:

(1) during the voyage, visit carefully and pay attention to the change of temperature.
Always be aware of the exhaust valve actuator supply pressure.
Sea condition in the outside world and the host under the premise of load constant, such as a cylinder exhaust temperature is gradually rising trend, abnormal sound, and so on and so forth, to correctly judge the fault timely, decisive measures, can effectively control the accident.
   

(2) strengthen the maintenance and management of the injector and ensure that the fuel injector works normally.
Hoisted out if nozzle bad, exhaust valve, obviously you can see from the nearest seat inside the nozzle, into the diagonal shape piled up a large amount of carbon and didn't burn out of fuel mixture, the surface into a liquid state, and flows downward to seal coupling surface, lead to carbon, the carbon, is the "culprit" burning valve, the two, is likely to be specific parts of the valve was burning.
   

(3) the engineer must inspect the exhaust valve regularly according to the requirements of the ship's diesel engine instructions.
   

(4) the valve disc and seat face are surfacing with heat resistant alloy. The general thickness is about 3mm, and the measurement is required according to the instruction manual when the inspection is taken, and the maximum grinding amount is Gt>
2.
The valve can no longer be used when the air gap G3 is less than or equal to O.
   

(5) in order to avoid caused by fluctuations in grinding disc surface vibration phenomenon, should as far as possible not in the ship sailing or breaks down grinding exhaust valve, if possible, as far as possible at the dock or professional manufacturer of grinding work.
   

(6) host the best interval for a period of time, the motor vehicles, roads in the fuel system with light oil to wash, is beneficial to improve the working condition of jet pump and fuel injector, improve the quality of combustion.
At the same time, the engineer should pay attention to the cooling of the combustion chamber parts, keeping the temperature of the parts below 550 degrees C, but the cooling water temperature cannot be set too low and the thermal stress is too large to crack.