What should I pay attention to when repairing motorcycle engines?

After nearly ten years of practical maintenance work, I have summarized the matters that should be paid attention to in motorcycle engine overhaul as follows, hoping to encourage you.

First, the operating environment should be dustproof and windproof, and the operation should be standardized.

Some motorcycle repair shops operate engines outdoors. No matter how dusty it is, they just focus on changing parts. You don't know that dust mixed into the machine will cause excessive wear and tear. In this environment, the new engine oil may be dirtier than the old engine oil, so the engine overhaul must be carried out indoors. In addition, the operation should be standardized, and the demolition should not be moved. If the CC 125 shifting cam and fork are replaced, the shifting mechanism can be replaced and repaired without opening the left engine case and disassembling the crankshaft. Misoperation will cause unnecessary trouble, not only delay work and time, but also may cause poor sealing of the side box. The prerequisite for repairing the engine is to know it like the back of your hand and carefully understand the structural diagram of the engine parts.

Second, it is essential to clean the engine housing before disassembly.

There was a lot of oil and dust accumulated on the engine shell during overhaul. If it is not cleaned in time, these impurities will be mixed into the engine body when the engine is disassembled, which will bring unnecessary wear to related components after installation. Furthermore, foreign matter falling into the engine will block the oil circuit, leading to poor lubrication, cylinder locking, shaft locking, clutch sintering and so on. In addition, if the engine case is not cleaned cleanly, there will be foreign objects stuck at the joint of the case, which will affect the sealing and cause oil leakage and oil leakage. Cleaning the engine housing can also prevent sludge from covering the bolts and avoid leakage. For example, the two fixing bolts in the middle box of Chongqing 80 engine are easily covered with sludge. If they are left outside and the package is forcibly opened, the engine box will be damaged.

Third, it is very important to mark it well.

Whether it is a mature model or a transitional model, there are many kinds of motorcycle engines with different structural characteristics. When we disassemble various engines, we should mark the installation of various accessories. Some nuts have the same thread but different appearance. Mark it well, and don't install it at will, because all kinds of nuts have certain torque requirements, and all kinds of shapes are determined through many experiments, which has certain scientific basis. If interchanged, it will affect its fixing effect and cause new failures. For example, the internal threads of the CG 125 clutch fixing nut and the oil filter nut at the right end of the crankshaft are the same. Although they can be installed interchangeably, they are different in shape and torque, and the torque of the clutch fixing nut is much greater than that of the crankshaft fixing nut. When we disassemble engines of unfamiliar models, such as CB 125T, CBR400, etc. We should mark the disassembled parts to prevent wrong assembly and missing assembly.

Four, the use of special tools, special appliances

The use of tools directly affects the quality and efficiency of maintenance work. This special tool is designed for the designated part of maintenance, which is scientific, easy to use, labor-saving and does not hurt accessories. If you are afraid of trouble and want to save money, illegally taking a tool will greatly reduce the quality of your work. For example, after the GY6 machine is disassembled, the clutch retaining nut can only be disassembled smoothly with 19# socket wrench and brake. It can be seen that some repair shops do not have special tools, just take a steel punch and roughly disassemble it, and then the nut is removed. How to tighten the deformed nut according to the specified torque? If the clutch retaining nut is loosened for a long time, the clutch assembly will fall off, and the consequences are unimaginable. Once a motorcycle friend's motorcycle was overhauled, the clutch fell off, causing the side box to rupture. Irregular operation can also damage the bearing at the inner end of the output shaft.

In addition, when we disassemble the engine, we should put the parts before and after cleaning in a special aluminum tray or wooden tray in order, and don't pile them up everywhere. Some small parts are easy to be lost, such as the semi-circular key of each crankshaft, piston pin retaining ring, various circlip gasket positioning pins, etc.

Fifth, the accessories are placed in an orderly manner.

When disassembling an unfamiliar engine, put all parts in place to prevent omission and incorrect assembly. For example, when replacing damaged parts, the removed parts should be arranged one by one from left to right, and then assembled in the opposite order after replacing them with new ones to avoid mistakes.

Six, the cleaning of related parts is very important.

Once the engine is disassembled, the gasket (paper, asbestos and other gaskets) will push the elastic force after use and promote the sealing effect. It can no longer be used, so it should be completely eradicated and replaced with new products. Furthermore, the gasket-free seal should be carefully removed with bamboo pieces (DX 100, AX 100, K 100, etc.), and then the genuine special sealant should be evenly applied and fastened. Use bamboo pieces to thoroughly remove the sludge and polish from the clearance between the removed parts, such as CG 125 oil filter and C 100 clutch. This work also determines the use of the engine after overhaul. Some repairmen only replace damaged parts, not tired oil seals, gaskets and snap rings, and do not clean up the sludge and impurities in the machine. After loading the shelf, the car can ride, but it won't be long before there will be new faults.

Seven, replacement parts should be carefully measured and compared.

The spare parts market is mixed. In order to ensure the maintenance quality, we should carefully compare the old and new parts when buying genuine products, and use special tools to actually measure them to ensure that the engine after overhaul is as good as ever. If the crankshaft, cylinder assembly and other parts are replaced, it is necessary to use vernier calipers to measure whether each part of the crankshaft assembly is standard or not, and to measure whether the cylinder plug ring is closely matched, so as to avoid finding out the fault after the assembly and debugging of the parts and wasting time and energy.

Eight, it is essential to apply lubricating oil when assembling parts.

When assembling the disassembled parts, apply a proper amount of new lubricating oil evenly on the joint parts of the parts, such as crankshaft and bearing, shift cam and box, shift gear and gear, cylinder plug ring, etc. With lubricating oil, the assembly will be smoother, and it is convenient to close the box, so as to avoid the dry and astringent assembly of parts, the difficulty in closing the box and the damage to parts.

Nine, choose standard gasket, use sealant with caution.

When assembling the engine, the choice of new sealing gasket can not be ignored. If non-standard gasket is selected, it will cause oil leakage and start-up difficulty (the air inlet of two-stroke vehicle leaks oil, which makes the mixture too thin and difficult to enter the vehicle), and even more seriously, it will cause oil circuit blockage and cause new faults. In particular, the requirements of cylinder gasket are strict, and defective products are easy to burn through. Asbestos gasket can not be used, too thick will affect the compression ratio, resulting in difficulty in starting the vehicle and weak driving. In addition, pay attention to rubber gaskets and sealing rings, such as rubber rings on crankshafts such as CY80, DX 100, AX 100, and rubber rings on carburetor interfaces. Sealant is rarely used in engine assembly, and can only be used in two-stroke automobile middle box assembly and CB cylinder head. Four-stroke automobile engine assembly generally does not need to be coated with a drop of sealant, such as gaskets and aprons at various joints on machines such as C 100, CG 125, CG 150 and GY6, which can play a good sealing role. Although applying sealant is beneficial to sealing, too much sealant will also block the oil circuit and cause new faults. If sealant is applied to the joints with aprons, the aprons will be stuck and the sealing effect will be lost, such as CG 125 and GY6 cylinder heads.

X. pay attention to replace the oil seal.

When the engine is overhauled, the removed oil seal will run in different degrees, so it should be replaced with new products properly to prevent oil leakage or gas mixture leakage, which will make it difficult to start. Oil seals of some large-displacement motorcycles or special-shaped motorcycles are hard to buy. If the oil seal of the original car is not well operated, the spring of the oil seal lip can be removed and cut off by about 5mm, and it can be used as usual.

Eleven, replacement parts, should be installed while debugging.

With standardized operation, correct installation and good debugging, nip in the bud and replace damaged parts. For example, when replacing the starting shaft of C 100, mark the position of the starting gear on the box with a hacksaw before disassembling the shaft. After installing a new starting shaft, close the box and try to start (not only to start smoothly, but also to ensure that the starting gear and gear do not interfere with each other after starting back to normal), and then tighten the fixing bolts. At the same time, try to see whether the gear of the transmission changes freely and clearly and whether the oil pump shaft is installed in place to avoid new faults.

Twelve, do a good job of waterproof

All wiring harnesses connected to the engine should be inserted in place to be waterproof and rainproof. After the engine is installed on the big frame, the wiring harness should be straightened out, so as to ensure the normal operation of the lighting and charging circuits. In addition, the waterproof sleeve should be installed firmly and the wiring harness should be fastened. If there is no waterproof cover, wrap it tightly with waterproof tape.

Thirteen, pay attention to the air balance hole hose.

I have seen many motorcycles after overhaul, and the rubber hose of the atmospheric balance hole disappeared. Over time, the balance hole is blocked by foreign objects, which leads to the high internal temperature of the engine, weak driving and no high-speed phenomenon. In addition, the hose is stuck on the big shelf at a discount, which will also cause the above phenomenon.

Fourteen, beware of two-stroke motorcycle tubing falling off or blocked by foreign objects.

After the engine is removed, the oil pipe should be plugged with clean 6# bolts in time to prevent foreign matters such as dust from entering. When installing the engine, the oil pipe should be straightened to prevent sticking, and both ends should be fixed with circlips to prevent new failures after falling off.

15. The grounding wire connected between the engine and the big frame shall be installed firmly.

Generally, there is a thick grounding wire between the engine and the frame of an electrically started motorcycle. Both ends must be grounded to avoid virtual connection, otherwise the starting motor will be weak and difficult to start.

Sixteen, engine fixed parts can not be omitted. I have seen motorcycle engines overhauled many times. The fixed part is either missing or missing. For example, if you miss the steel-rubber sleeve flexibly combined with the engine and the big frame, it will cause the engine to vibrate, make the driver feel uncomfortable and even cause driving danger. Chongqing 80, Jetta 100 and Jincheng 90 all have this structure. In addition, the long-term absence of flat pads and spring pads on the engine fixing bolts will lead to engine looseness and affect driving safety.