As a core component of the engine's fuel supply system, wear on the rotary valve carburetor can directly affect the accuracy of the fuel-air mixture, leading to reduced engine power, increased fuel consumption, and even starting failure. Professional rotary valve repair requires a systematic approach that considers material properties, wear mechanisms, and the overall carburetor structure.
Rotary valve wear typically manifests as an increased gap between the valve body and seat, scratches on the sealing surface, or deformation of the mating surface. This type of wear is often caused by the impact of impurities in the fuel, prolonged high-frequency friction, or thermal deformation. Before repair, the carburetor must be thoroughly disassembled and an ultrasonic cleaner must be used to remove carbon deposits and oil stains from the valve body, seat, and rotating shaft to ensure the accuracy of subsequent inspections. If cracks occur in the valve body or seat, prioritize assessing whether repair is feasible. Minor cracks can be repaired using low-temperature welding, but the heat-affected zone must be carefully controlled to avoid annealing or deformation.
For seal surface wear, if the wear depth does not exceed one-third of the material thickness, precision lapping can be used to restore the fit. During the specific operation, after the valve body and valve seat are aligned, a lapping machine is coated with a mixture of alumina powder and engine oil. The machine is then rotated slowly in a figure-eight pattern to form a uniform, reticulated pattern on the contact surfaces. During the lapping process, the gap should be continuously checked with a feeler gauge to ensure that the final gap is within the specified range. If wear is severe, the sealing surface must be repaired through a hardfacing process. A nickel-based alloy welding rod with a thermal expansion coefficient similar to that of the base material is used. After layered hardfacing, the weld is then precision machined to the original dimensions.
When repairing shaft wear, the focus should be on restoring coaxiality. If the journal wear is minor, the shaft diameter can be thickened through chrome plating and then honed to the desired fit. If the wear is extensive, a custom shaft replacement may be necessary. During assembly, a high-temperature grease containing molybdenum disulfide should be applied between the shaft and bearing to reduce starting friction and form a dry film lubrication layer, slowing further wear. The coaxiality between the shaft and carburetor housing should also be checked. If deviation exceeds the allowable range, correction should be made by modifying the housing locating holes or installing adjusting shims. For valve body deformation caused by material fatigue, if the deformation does not cause structural failure, low-temperature stress relief can be used to restore the deformation. The entire carburetor is heated to below the material's tempering temperature, held at that temperature, and then slowly cooled to eliminate internal residual stresses. If the deformation is severe, a hydraulic correction device is required to apply a counter-torque to gradually restore the valve body geometry. After correction, key dimensions are inspected using a coordinate measuring machine to ensure compliance with design tolerances.
The repaired rotary valve requires leak testing and functional verification. The carburetor is connected to a simulated test bench, and leakage at different openings is checked using a negative pressure tester. If the leakage rate exceeds the standard, the valve body clearance must be readjusted or the seals replaced. The carburetor should also be operated on an engine test bench to monitor idle stability, acceleration response, and fuel consumption to ensure that the repaired carburetor meets original manufacturer performance specifications.
During routine maintenance, it is recommended to perform a special inspection of the rotary valve carburetor every certain mileage or quarterly, focusing on cleaning the air filter to prevent impurities from entering the valve body. Before parking a vehicle for an extended period, add an anti-corrosion additive to the fuel to slow down the oxidation of the valve body material. Systematic repair and preventive maintenance can significantly extend the life of the rotary valve carburetor and ensure reliable engine operation.
