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Wear Characteristic Identification and Repair of Plunger Oil Pump
The plunger coupling is a critical component in fuel injection systems, and understanding its wear characteristics, identification methods, and repair procedures is essential for maintaining engine performance. Below is a detailed overview of the wear patterns, inspection techniques, and repair strategies for both the plunger and valve components.
**1. Wear Characteristics of the Plunger Coupling**
- **Plunger Head Wear:** The most significant wear occurs on the plunger head where it contacts the cylinder. The surface shows shallow grooves with a coarse texture, often appearing milky white. These grooves can be up to 0.023–0.025 mm deep, with widths of 4–5 mm and lengths of approximately 10 mm. The wear is more pronounced under light, indicating localized stress points.
- **Beam Wear:** The beam area experiences less severe wear compared to the plunger head. It typically exhibits comb-shaped furrows, with deeper grooves visible under magnification. The texture varies from rough to fine, depending on the location.
- **Stop Edge Wear:** The edge of the plunger stop wears gradually from the top downward. The worn area is about 5 mm wide and appears milky white. The edge becomes rounded and blunt due to prolonged use.
- **Lower Shoulder Wear:** This area shows minimal wear, usually in the form of short, linear marks around the shoulder circumference.
- **Plunger Sleeve Wear:** The most noticeable wear occurs near the oil hole, particularly on the back side. The wear extends upward by 6–7 mm from the top edge of the hole, reaching a depth of 0.024–0.027 mm. Downward wear extends 4.5 mm from the bottom edge, with a depth of 0.015–0.017 mm. The wear width exceeds the hole diameter, indicating potential misalignment or excessive friction.
**2. Identification of the Plunger Coupling**
- **Visual Inspection:** A thorough visual check is the first step. Look for signs of wear such as milky white discoloration, scratches, rust, cracks, or flaking on the plunger head or edges. Any of these defects indicate that the plunger should be replaced.
- **Vacuum Test:** Cover the plunger hole with your index finger and pull the plunger outward with your other hand. If the plunger retracts quickly due to suction, it indicates proper sealing. If not, further inspection or replacement may be needed.
- **Sealing Test:** Connect the plunger to an injector tester and apply pressure up to 22,540 kPa. Measure the time it takes for the pressure to drop from 19,600 kPa to 9,800 kPa. The acceptable range is 16–29 seconds. If the time is outside this range, the plunger may need repair or replacement.
**3. Repair of the Plunger Coupling**
- **Grinding the Upper End:** If the upper end of the plunger sleeve is uneven, use a 600-grit abrasive-coated glass plate to grind it smooth. Apply even pressure while rotating and changing direction to ensure uniformity.
- **Blocking Issues:** If the plunger is too tight within the sleeve, apply oil and perform mutual grinding. For severe cases, use a hand drill to adjust the fit. Remove burrs from the plunger tip using an 800-grit stone and slight tilting.
- **Replacement:** In cases of severe wear, replacing the entire plunger coupling is recommended to ensure optimal performance.
**Second, Oil Valve Wear Characteristics, Identification, and Repair**
**1. Wear Characteristics of the Oil Valve Components**
- **Sealing Cone Wear:** The sealing cone is the most vulnerable part, showing increased wear and reduced finish. A ring groove forms, typically 0.05 mm deep.
- **Decompression Ring Wear:** The decompression ring tends to taper after wear, with the lower edge becoming rounded. Surface grooves are shallow but widespread.
- **Guide Surface Wear:** The guide portion experiences less wear than the sealing cone, but still shows some degradation, especially near the valve seat.
**2. Identification of the Oil Valve**
- **General Inspection:** Check for serious wear, milky white scratches, or axial notches on the decompression ring. Also, look for excessive wear on the sealing cone, rust, or metal peeling on the valve seat.
- **Seal Test:** Perform a simple seal test by covering the valve seat with your thumb and pressing the valve into place. If air is drawn in and the valve bounces back, the seal is good. Otherwise, repair or replace the part.
- **Sliding Test:** Soak the valve in diesel and test its movement. It should slide smoothly and return to position without sticking.
**3. Repair of the Oil Valve**
- **Sealing Cone Repair:** If the sealing cone is slightly worn, apply abrasive paste and rotate the valve in the seat. Repeat the process in different directions, avoiding contact with the decompression ring. After grinding, clean the parts and test the seal again.
By following these steps, you can effectively assess and maintain the performance of plunger and oil valve components, ensuring reliable operation of the fuel injection system. Regular inspections and timely repairs are crucial for extending the life of these critical parts.