Common valve failure mode

 Valve fracture caused by the impact between piston and valve. In the operation of the engine, the valve and the piston should not be in contact with each other under any circumstances. Even a slight contact will cause the valve to break, which is manifested in the face of the top of the piston and the valve®

The corresponding position has repeated impact marks consistent with the size of the valve disc, and there is no carbon deposit on the end face of the valve disc, showing a bright surface of rotary friction. (See Figure 1)

■ Rocker arm and valve contact position is not correct, valve

The rod end will be subjected to lateral thrust, which will cause the clamping groove of the air door lock to break. The reproduction form is obvious wear marks on the end face of the valve rod by side thrust. (See Figure 3)

■ The out-of-tolerance coaxiality between the valve conduit and the valve seat ring will make the neck and disc of the valve subject to the alternating bending stress caused by the unilateral seat, resulting in the fracture of the valve neck or disc block. Its reproduction form is that the valve stem has obvious unilateral wear or abnormal wear marks, the valve cone and the seat ring contact position offset, and often accompanied by the valve does not rotate. (See Pictures 5, 6 and 7)

■ Should not exist in the exhaust gas solid particles and abnormal chemical corrosion substances and high temperature lead to valve cone

Pitting, serious will cause local ablation of valve cone or disk cracking damage. (See Pictures 9 and 10)

■ The valve disc end face is not allowed to mark or grind the valve percussion, otherwise, the local stress concentration will lead to cracking. (See Figure 17)

■ The actual operating temperature of the valve is higher than the designed operating temperature limit of the engine valve, resulting in local valve material annealing, metallographic structure transformation, mechanical strength reduction, disc deformation and valve neck fracture. (See Figure 18)

■ Pay attention to valve spring fracture, valve seat ring off, timing belt fracture or tooth loss, valve duct fracture, valve phase error, engine overspeed (speed) and other reasons can lead to valve good effect.

■ When the lock clamp falls off the valve, if the lock clamp is not selected correctly, installed poorly or subjected to strong vibration impact, the lock clamp will fall off or fail, and the valve will fall into the cylinder. The manifestation is that the air lock clamp slot is intact and the valve rod is bent. (See Figure 2)

In the

■ If the inner rib of the lock clip is not in line with the shape of the air door lock clip, the lock clip clip will be hurt, resulting in obvious traces of snapping on the slot. In the form of reappearance, obvious traces of rodents can be seen in the lock groove. (See Figure 4)

■ If the valve duct gap is out of tolerance, it will cause the valve to swing in the process of movement, abnormal wear of the rod, valve temperature rise, improper setting and uneven force, etc., leading to valve failure. (See Figure 8)

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■ High temperature gas escapes from the valve cone and seat ring where the contact is not tight. Causing local ablation of valve cone (commonly known as "burn") (see FIG. 11, FIG. 12)

■ The gap between the inner hole of the conduit and the valve rod diameter is smaller than the relevant regulations or poor lubrication leads to abnormal valve movement, serious wear or valve damage. (See Pictures 13 and 14)

■ Poor inlet valve cleanliness, improper valve clearance, large impact on the seat ring when sitting, valve rotation too fast, leading to abnormal valve cone wear. (See Pictures 15 and 16)

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