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(1) Gearbox housing 1) The mating surfaces between the upper and lower halves of the gearbox housing must be airtight; to check this, use a 0.05 mm feeler gauge – it should not fit into any part along the entire perimeter. In those areas where it does fit in, the depth of insertion shall not exceed 1/3 of the width of the sealing surface. There shall be no grooves that run through the mating surface along the entire perimeter. 2) Kerosene should be used to check for leaks in the lower speed reduction gearbox; there should be no oil leakage or soaking. 3) When during maintenance it is found that the gear mesh line is skewed, the meshing is poor, the tooth surfaces are worn, or the noise level increases during operation, a precision dummy shaft should be used to check the parallelism of the two gear shafts; the deviation in parallelism should be within 0.025 mm, and the maximum allowable deviation in center distance must not exceed 0.10 mm. When the parallelism error is within 0.10 mm, it can be addressed by dressing the bearing; otherwise, a treatment plan should be developed or the gearbox replaced. 4) Use a level to check the camber of the gear shafts inside the two gear bearing housings; the direction of the camber of the two gear shafts should be the same. 5) With the foot bolts properly tightened, check the levelness of the lower box body, taking into account both vertical and horizontal levels, and ensure that the deviation of the box body’s horizontal surface is within 0.02 mm. (2) Large and small gears: 1) The tooth surfaces of the large and small gears must be free from defects such as wear, bonding, pitting, flaking, or burning; if the defects are severe, the gears should be replaced. 2) The journal of the gear shaft shows no wear or other damage, and both the cylindricity and roundness deviations of the journal are within 0.015 mm. 3) The working surface of the shaft end coupling is free from defects such as grooves, scratches, and cracks. 4) The gears are inspected using dye penetrant testing. 5) When unexplained vibration increases during operation and no other cause can be identified, the gear together with the coupling should be dynamically balanced. The dynamic balance accuracy should ensure that the mass imbalance eccentricity of the gear is less than 0.5 μm. (3) Assembly 1) Use the lead pressing method to check the side clearance and end clearance on the meshing sides of the large and small gears. 2) Use the coloring method to check the tooth surface contact; the contact rate along the tooth width direction should be 85%, and that along the tooth height direction should be 55%, with uniform contact marks. 3) Check the contact between the gear shaft journal and the lower half of the radial bearing; the contact area within a 60-degree range at the bottom of the lower half should be over 80%. The angular deviation of the side clearance of the lower bearing should not exceed 0.05 mm when checked with a feeler gauge. 4) Check the clearance of the thrust bearings; if it is out of spec, the bearings should be replaced. The contact area between the working end faces of the thrust bearings on both sides should be over 80%. After the upper and lower bearings are fitted together, check that there is no misalignment at the mid-segment end face, and that the clearance at this joint does not decrease. 5) Once the gearbox is assembled, the large gear should rotate smoothly when the operating handle is turned. Check the clearance of the thrust bearing in the large gear to ensure it remains the same as before the cover was installed. 6) The fuel injector is installed in the correct position and securely; its orientation and location meet the lubrication requirements, and the injector is unobstructed.