Ignition systems that send sparks to the spark plugs have been contactless, such as transistor ignition and CDI ignition, since the 1980s, but prior to that, they were controlled by opening and closing contact points. Both the sliding point heel and the point contact point, which interrupts the flow of electricity, were consumable parts and required regular maintenance and replacement. Moped class points are often fitted inside the flywheel and the flywheel must first be removed to reach the points.
Removing the flywheel is not just for engine overhauls.
The flywheel attached to the end of the crankshaft is a bouncing wheel that smoothes the rotation of the engine, but its role is slightly different for automobiles and motorcycles. While the flywheel for automobiles is located between the engine and the gearbox and is used to interrupt the power, the flywheel for motorcycles differs depending on whether the engine is first mounted vertically or horizontally, that is, whether the crankshaft is facing the direction of travel or straight ahead.
Longitudinally mounted engines on motorcycles are limited to a few models such as BMW and Gold Wing, while most other models, from mopeds to big motorcycles, are equipped with transversely mounted engines. The crankshaft is then orthogonal to the direction of travel, so the flywheel is attached to the side of the body. In this case, the flywheel may be used as part of the ignition system.
Specifically, this applies to models from the moped class to the mid-size class. In addition, many flywheel magneto & point ignition engines from the 1980s and earlier have a flywheel that plays an important role in point intermittence. Spark plug ignition timing is very important to the engine and requires accurate capture of piston movement.
In this case, the angle of the flywheel directly connected to the crankshaft is most appropriate for determining the piston position. In the case of a flywheel magneto type ignition system, the electricity required for ignition is generated by the interaction between the magnet built into the flywheel and the coil fixed to the crankcase, so there is also a rationale for installing the points near the coil.
For these reasons, maintenance of the ignition system is not easy for small exhaust models with contact breakers built into the flywheel. When opening and closing the point contacts, which carry high voltage, sparks fly onto the surface of the points, causing the surface to become rough, and the point cam and point heel, which open and close the points, are worn as they rotate and slide while making contact. Then, as the mileage increases, the timing at which the points open and close gradually shifts, and the ignition timing also changes, resulting in a deterioration of the engine's condition.
When the ignition timing is off, a screwdriver is inserted from the outside of the flywheel to fine-tune the position of the contact breaker so that the timing of the point opening matches the "F" stamped on the outside of the flywheel indicating ignition timing. However, as the point and heel wear progresses, adjustment alone will no longer be sufficient, and the contact breaker itself will need to be replaced.
- Point 1: Some motorcycle engine models have an ignition system built into the flywheel at the end of the crankshaft.
- Point 2:If the contact breaker for point ignition is located inside the flywheel, the flywheel must be removed when the breaker is replaced
Flywheel puller is used in combination with flywheel holder
To replace the contact breaker inside the flywheel or the condenser that functions as a set with the breaker, the flywheel itself must be removed. The crankshaft and flywheel are tapered to each other and are tightly fitted together by tightening a central bolt or nut. Therefore, the flywheel cannot be removed simply by removing the bolts and nuts; a special tool, the flywheel puller, is required.
Observing the flywheel, there is a screw in the center. When a flywheel puller compatible with this screw diameter is installed and the center push bolt is screwed in, the crankshaft end is pushed and the flywheel is released toward the front. The flywheel side threads come in several sizes, and the versatile flywheel puller comes with several different threads for use with different flywheels.
Here we introduce the case where the flywheel screws are female thread type, but depending on the model, the flywheel side may have male threads and a female thread type flywheel puller may be required.
Furthermore, when using a flywheel puller, a turnstopper must be set to prevent the flywheel from turning together when the puller is tightened. If there is a hole or slit on the outer surface of the flywheel, a pin-type holder should be set to prevent the flywheel from turning, while a band-type pulley holder should be used for flywheels without a hole for a pin.
If you get a discontinued moped model and the spark plug does not skip sparks no matter how many times you depress the kick pedal, you need to check the flywheel and, if it was a points ignition, check the ignition timing and points condition. As a result, remember that you will need a flywheel puller and an anti-turn holder when replacing the contact breaker inside the flywheel.
- Point 1: Flywheel screws come in various sizes and require a flywheel puller suitable for the screw size.
- Point 2: The holder that stops the flywheel from turning and the flywheel puller should be used as a set.