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Repair of valve and valve seat damage

2022-08-25

 When the valve seal is not tight or the sag is too large, the valve needs to be removed for maintenance, repair or replacement. To remove the valve, first remove the cylinder head cover, remove the valve rocker arm assembly, remove the high-pressure fuel pipe, remove the fuel injector, unscrew the cylinder head nut, and remove the cylinder head. Then press the valve spring seat with the special tool for dismantling the valve, compress the inner and outer springs of the valve, take out the valve lock clip, after loosening, remove the inner and outer springs of the valve, and then the valve can be taken out. After the valve is removed, it should be marked and must not be replaced during assembly. Using a dial indicator and V-bracket, measure valve stem flex. During inspection, the valve stem is supported on two V-shaped frames with a distance of 100 mm, and then use a dial gauge to check that 1/2 of the valve length is the curvature. If it exceeds the allowable limit, it should be corrected with a hand press.

When the valve is slightly leaking, it can be ground to restore its tightness. Before grinding the valve, the valve, valve seat and guide tube should be cleaned. Through the selection, the valve head subsidence of each cylinder should be consistent, and marks should be made on the top of the valve head to avoid confusion. The manual grinding method is as follows:

(1) Put a soft spring on the valve stem, apply a layer of valve sand on the valve slope, apply lubricating oil on the valve stem, and insert the valve into the guide tube. The valve sand is divided into two types: coarse sand and fine sand. The selection depends on the degree of burning of the valve bevel and the valve seat bevel. To directly grind the used valve, you can use coarse sand to grind first, and then use fine sand for fine grinding. If the valve bevel is repaired by smooth grinding, the valve seat is repaired by reaming, and the bevel is complete, it can only be ground with fine sand.

(2) Use a valve grinding screwdriver or rubber twister to rotate the valve back and forth (the angle of rotation should be less than 180°) for grinding. During the grinding process, the lifting and pressing actions should be performed along the rotating surface of the valve to change the running-in position of the valve and the seat to ensure uniform grinding. When grinding, do not use excessive force, do not raise the valve, and hit the valve seat with force to avoid widening the bevel or grinding out concave grooves.

(3) When the valve and the valve seat slope are ground into a complete and smooth annular belt, it means that the grinding has been completed. The valve sand can be washed, and oil is applied to the slope, and then ground for 3 to 5 minutes. During the grinding process, do not use too much valve sand to prevent loss and wear of other mating surfaces.

(4) The ground contact slope should be smooth and clean, and the contact width is generally 1. 5 to 2. 0 mm. Put the valve on the matching valve seat, and then tap the valve head several times. If a continuous, bright gray halo appears in the middle of the valve working surface, it means that the valve is in normal contact with the valve seat. Or draw a soft pencil line every 4 mm on the working surface of the valve, then insert the valve into the valve guide and valve seat, turn 1/8 to 1/4 turn, or tap a few times, if the pencil lines are all in the middle of the belt Interrupted, indicating that the valve and valve seat are well sealed.