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After nearly ten years of actual maintenance work, I have summarized the matters that should be paid attention to during motorcycle engine overhaul as follows, and I hope to encourage everyone.

1. The operating environment must be dustproof and windproof, and the operation must be standardized. Some motorcycle repair shops overhaul engines outdoors. They only care about replacing parts regardless of how dusty they are. You may not know that dust mixed into the engine will cause undue abrasive wear. In this environment, the new engine oil may be dirtier than the old oil. Engine overhaul must be performed indoors. In addition, the operation must be standardized, dismantle what should be dismantled, and do not touch what should not be moved. If the CC125 transmission cam and shift fork are replaced, the transmission mechanism can be replaced without opening the left engine case and removing the crankshaft. Improper operation will cause unnecessary trouble, not only lost work and time, but also may cause the side box to be poorly sealed. The prerequisite for repairing an engine is to know it well and carefully understand the engine component structure diagram. 2. It is essential to clean the engine casing before disassembly. There is a lot of oil and sand accumulation on the engine casing during overhaul. If not cleaned in time, these impurities will be mixed into the interior of the engine when the engine is disassembled. After installation, it will cause unnecessary damage to related components. of wear and tear. Furthermore, if foreign objects fall into the engine, they will block the oil passages, which may lead to poor lubrication, cylinder locking, shaft locking, clutch sintering, etc. In addition, when the engine casing has not been cleaned, foreign objects will get stuck at the joints of the boxes when they are closed, affecting the sealing and causing oil leakage. Cleaning the engine casing can also prevent sludge from covering the bolts and preventing them from being disassembled. For example, two of the Chongqing 80 engine middle box fixing bolts are easily covered by sludge. If they are missed and forced to be unboxed, the engine box will be damaged. 3. It is important to make good marks. Whether it is a mature model or a transitional model, there are many types of motorcycle engines with different structural characteristics. When we disassemble various engines, we should mark the installation of various accessories. Some nut threads are the same, but have very different appearances. They should be marked and cannot be installed arbitrarily, because various nuts have certain torque requirements. Various shapes are determined through many experiments and have a certain scientific basis. If they are interchanged, their fixing effect will be affected and new faults will occur. For example, the CG125 clutch fixing nut has the same internal thread as the oil filter nut at the right end of the crankshaft. Although they can be installed after interchange, they have different shapes and different torques. The clutch fixing nut has a much greater torque than the crankshaft fixing nut. When we disassemble an engine that we are not familiar with, such as CB125T, CBR400, etc., we should mark the disassembled parts to prevent misinstallation or missing installation. 4. Use special tools and special utensils. The use of tools directly affects the quality and efficiency of maintenance work. Special tools are designed for repairing specified parts. They are scientific, easy to use, save effort, and do not damage accessories. If you are afraid of trouble and want to save money, using random tools and operating them in violation of regulations will greatly reduce the quality of work. For example, when disassembling the rear clutch fixing nut of a GY6 machine, you need to use a 19# socket wrench and the brake to remove it smoothly. It can be seen that some repair shops do not have special tools and just use a steel punch to disassemble it brutally. The nut was removed and the nut was deformed. How can I tighten to the specified torque again? If the clutch fixing nut becomes loose over time, the clutch assembly will fall off, with disastrous consequences. Not long after a motorcyclist's motorcycle was overhauled, the clutch fell off and the side case cracked. Irregular operation can also damage the bearing at the inner end of the output shaft. In addition, when we disassemble the engine, the parts before and after cleaning should be placed in order on a special aluminum plate or wooden plate. They should not be piled up anywhere. Some very small parts are easily lost, such as the semicircular keys of each crankshaft. , piston pin retaining rings, various circlip gasket positioning pins, etc. 5. Arrangement of accessories. When disassembling an unfamiliar engine, place the parts in order to prevent missing or incorrect installation. For example, when replacing damaged parts of the engine gear shift mechanism of each vehicle, arrange the disassembled parts one by one from left to right, and assemble them in the reverse order after replacing new ones to avoid errors. 6. Cleaning of related parts is very important. Once the engine is disassembled, each gasket (paper, asbestos and other gaskets) will be elastic after use and promote the sealing function. It cannot be used again and should be completely removed and replaced with new products. Furthermore, use bamboo chips to carefully remove the failed sealant from the gasketless sealing area (two-stroke engine middle boxes such as DX100, AX100, K100, etc.), and then evenly apply the genuine special seal glue box to tighten it. The sludge and grinding in the disassembled parts and the matching gaps of each machine part should be completely removed with bamboo chips, such as hard debris in the CG125 oil filter and C100 clutch.

This work also determines the use of the engine after overhaul. Some maintenance workers only replace damaged parts, but do not replace tired oil seals, gaskets, and circlips, nor do they clean the oil sludge and impurities in the machine. After the machine is installed and put on the shelf, although the car can be ridden, it will not take long before new faults will appear. 7. When replacing parts, you must carefully measure and compare them. The parts market is crowded. In order to ensure the quality of repairs, when purchasing genuine products, you must also carefully compare old parts with new parts. Use special tools to actually measure. It is required that the engine after overhaul is intact. For example, when replacing crankshafts, cylinder components and other mechanical parts, use vernier calipers to actually measure whether the crankshaft assembly is standard and whether the cylinder plug rings are in tight fit, so as to avoid discovering faults only after the parts are installed and running the test, which would cause delays and time-consuming work. 8. The application of lubricating oil is indispensable when assembling parts. When assembling the disassembled parts, take an appropriate amount of new lubricating oil and apply it evenly to the joint parts of each part, such as the crankshaft and bearings, the shift cam and the box, the shift gear and gears, and the cylinder. Applying lubricating oil between the plug rings and other parts will make the assembly smoother, so as to facilitate the tight closing of the box, and avoid dry and astringent parts of the assembly, making it difficult to close the box, which may cause damage to the machine parts. 9. Use standard gaskets and use sealants with caution when assembling the engine. The selection of new gaskets cannot be ignored. If non-standard gaskets are selected, it will cause oil leakage and difficulty in starting (two-stroke vehicles have air intake leakage, causing The mixture is too thin, so it is difficult to start the car), or even worse, it will cause the oil line to be blocked and cause new faults. Especially the upper cylinder gasket has strict requirements, and defective products are very easy to burn through. If asbestos should be used, aluminum gaskets cannot be used. Too thick will affect the compression ratio, making the vehicle difficult to start and unable to drive. In addition, pay attention to the rubber gaskets and sealing rings not to be missed, such as the rubber rings on the crankshafts of CY80, DX100, AX100, etc., and the rubber rings on the carburetor interface. Sealant is rarely used during engine assembly. It is only used when assembling the center box of two-stroke vehicles and on the cylinder head of CB engines. Generally, there is no need to apply a drop of sealant when assembling four-stroke vehicle engines, such as C100, CG125, CG150, GY6, etc. The gaskets and rubber rings at each joint on the machine can seal well. Although applying sealant is good for sealing, too much sealant will clog the oil circuit and cause new failures. If sealant is applied to the joint with the rubber ring, the rubber ring will be stuck and the sealing effect will be lost, such as the CG125 and GY6 cylinder heads. 10. Pay attention to the replacement of oil seals. When the engine is overhauled, the relevant oil seals that have been disassembled and assembled will operate to varying degrees. They should be replaced with new ones appropriately to prevent oil leakage or mixture leakage, which may cause difficulty in starting. It is difficult to purchase oil seals for some large-displacement motorcycles or special-shaped motorcycles. If the original oil seal is not very operable, you can remove the spring from the lip of the oil seal and cut off about 5mm, and you can use it as usual. 11. When replacing accessories, you must install and debug them at the same time. When replacing damaged accessories, you must standardize the operation, install them correctly, and debug them well to nip them in the bud. For example, when replacing the C100 starter shaft, before removing the shaft, use a hacksaw blade to mark the position of the starter gear on the box. After installing the new starter shaft, close the box and try to start it (not only must the startup be smooth, but also the startup gear must be returned to normal). After the gears are in position, the starting gear and each gear do not hinder each other), then tighten the fixing bolts, and at the same time test whether the transmission gears can move freely and clearly, and whether the oil pump shaft is installed in place to avoid new faults. 12. Do a good job of waterproofing. All wiring harnesses connected to the engine must be plugged in place to ensure waterproofing and rainproofing. After the engine is installed on the frame, the wiring harness should be straightened out and the plugs should not be missed to ensure that the lighting and charging circuits are working properly. In addition, the waterproof cover should be installed firmly and the wiring harness should be firmly clamped. If there is no waterproof cover, it should be tightly wrapped with waterproof tape. 13. Pay attention to the proper installation of the atmospheric balance hole hose. I have seen many motorcycles that have been overhauled. The atmospheric balance hole hose has been missing. Over time, the balance hole has been blocked by foreign objects, causing the internal temperature of the engine to be too high, causing the vehicle to be unable to drive and no high speed. In addition, the hose is discounted and stuck on the frame, which will also cause the above phenomenon. 14. Beware of two-stroke motorcycle oil pipes falling off or being blocked by foreign matter. After the engine is removed, the oil pipe should be plugged with a clean #6 bolt in time to prevent dust and other foreign matter from entering. When installing the engine, the oil pipe should be straightened out to prevent it from getting stuck, and both ends should be fixed with circlips to prevent it from falling off and causing new faults. 15. The ground wire connecting the engine and the frame must be installed firmly. Generally, on electric-start motorcycles, there is a thick ground wire between the engine and the frame. Both ends must be solid to avoid virtual connections, otherwise, it will As a result, the starter motor is weak and difficult to start.

16. Engine fixing parts must not be missing. I have seen motorcycle engines that have been overhauled many times. The fixing parts are either missing or missing. For example, the steel-glue combination sleeve that flexibly combines the engine and the frame is missing, which will cause The engine vibrates, making the driver feel very uncomfortable and even causing driving danger. Chongqing 80, Jetta 100, Jincheng 90, etc. all have this structure. In addition, missing the flat washers and spring washers on the engine fixing bolts will cause the engine to loosen over time, affecting driving safety.