market dynamics
Motorcycle maintenance should pay attention to the problem
Release date:2023.09.14

Due to the uneven technical level of the maintenance service personnel, it is easy to ignore some insignificant small parts in the maintenance process of the motorcycle, resulting in different degrees of hidden trouble and quality problems of the motorcycle after maintenance, affecting its service life. The problems that are easy to ignore in the circuit, oil circuit, gas circuit and mechanical part of motorcycle maintenance are discussed with customers, friends and maintenance personnel.

I. Minimum ignition speed of the ignition system

Under normal circumstances, the magneto ignition system is set with a minimum ignition speed, which can ensure that the ignition system can achieve high pressure ignition at a lower engine speed. However, when most maintenance workers check the ignition system failure, most of them are to remove the spark plug on the faulty engine and put it on the high pressure damping cap for fire jump test. This method is simple and easy, and has been widely used by maintenance workers. However, some electrical failures of the engine that are difficult to start are caused by the high voltage pack and the electronic igniter's low speed ignition speed. If the minimum ignition speed of the Honda CH125 water-cooled scooter ignition system is 300r/min, if the minimum ignition performance decreases, the minimum ignition speed will rise, and some even reach 400r/min or more to normal ignition, if the simple spark plug test method is still used, it will be confused by some illusions, and even mislead maintenance personnel. This is because the engine without a spark plug, when the piston is running up and down, there is basically no compression resistance in the cylinder, and the starting speed is about 400r/min or more, which is much higher than the speed when there is a spark plug. From the appearance, the spark plug does have sparks at this time, but when it is installed on the engine to use electric start or foot start, because there is a certain gas pressure in the cylinder, its operating resistance is increased, and the starting speed is only about 300 r/min. If the battery voltage is low, the starting speed is lower at this time, which cannot meet the minimum ignition speed of the ignition system, and the motorcycle cannot start, of course.

Therefore, when using spark plug or high pressure pack fire test, it is necessary to install a spark plug on the faulty engine, and when conditions are available, it is best to measure the starting speed with an electronic tachometer. If the starting speed of the old battery (voltage is about 12V) is 300r ~ 350r/min, the spark plug is weak, and the starting speed of the new battery (voltage above 13.5V) is more than 400 r/min, the spark plug is blue and white, you can draw a preliminary conclusion: The engine may have a high minimum ignition speed fault. The fault can be completely eliminated by testing the performance of various electrical appliances in the ignition system, replacing the ignition coil and the electronic igniter for comparative test.

2. Ignition trigger gap or air gap is too large

The ignition system of the motorcycle engine generally uses the flywheel rotor magneto, that is, the magnet and the flywheel into one, as part of the engine flywheel, the permanent magnet rotates with the flywheel, forming a magnetic field, generating induction current in the fixed armature coil, and playing the role of storage and release of mechanical energy. When a four-stroke engine adopts a contactless ignition system, its magneto trigger coil is set outside the flywheel rotor with a permanent magnet. When the rotor rotates, the trigger coil induces pulse current to provide trigger signal to the electronic igniter (CDI) device.

In order to ensure that the ignition system has a strong ignition trigger signal and does not interfere between the trigger magnetic pole and the flywheel rotor boss, a trigger gap of 0.40mm ~ 0.80mm is designed between the trigger coil magnetic pole and the flywheel rotor boss. Under normal circumstances, this gap can be adjusted by the mounting through hole (some oval holes) arranged on the trigger coil pole seat. Due to the error of parts manufacturing, the reinstallation of the part during repair, or the wear of the magnetic pole of the trigger coil, the ignition trigger gap sometimes becomes large, so the ignition performance of the engine is affected to different degrees. Similarly, a certain air gap is also required between the outer circle of the stator and the inner wall of the magnetic cylinder of the flywheel rotor. Under normal circumstances, the unilateral air gap should be no more than 0.75mm (as shown in Figure 2) to ensure the normal operation of the magneto ignition and charging system.

A 125 motorcycle driving more than 43,000 kilometers, due to the excitation coil failure to replace the stator assembly after the foot start normal and electric start does not fire fault. The maintenance worker checks that the static and dynamic voltage of the battery is normal, the overrunning clutch, starting line and relay are all normal, and then checks the starting motor connection line and motor carbon brush and other related parts, no fault trace is found. Remove the spark plug and put it on the damping cap of the high pressure pack to check the electric start, the spark is dark red, and the electric start is still not effective after replacing the spark plug. Considering that the stator coil has been replaced (the stator coil and the trigger coil are connected to the same harness), the air hood is removed, and the gap between the flywheel boss and the magnetic pole of the trigger coil is about 2.0mm. Recalibrate its trigger gap to the standard value of 0.50mm, reinstall the parts, electric start once successful, troubleshooting.

Another 125 scooter, due to magneto flywheel rotor loss of magnetism, replacement of new parts after the vehicle can not start. After several twists and turns to find the root of the fault, the original replacement of the flywheel rotor inner wall diameter is slightly larger, and the stator outer circle clearance exceeds the specified value. Replace the genuine magneto flywheel and check that the gap between the outer circle of the stator and the inner wall of the flywheel rotor magnetic cylinder does not exceed 0.50mm. Assemble the removed parts, start the engine, one success, confirm that the fault is rectified.

It can be seen from the above example that when the maintenance worker replaced the stator assembly, he did not adjust the trigger gap according to the regulations, so that the ignition trigger gap is too large. When the foot is used to start, the starting speed can barely reach because of the large recoile inertia. When the electric start, because the speed of the starting motor is relatively low, the trigger gap is too large to weaken its pulse signal, and the electric spark is not strong enough to start. The other motorcycle is due to the excessive air gap between the outer circle of the stator and the inner wall of the flywheel rotor magnetic cylinder, which seriously affects the ignition performance of the magneto, and also causes the vehicle to fail to start.

Here to remind maintenance personnel, in the investigation of motorcycle ignition system failure, do not ignore the ignition trigger gap and stator outer circle and flywheel inner wall air gap inspection.

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