Good Spark Needed for the Engine | What is the Intuition Behind Point Ignition Adjustments Common in Discontinued Motorcycles? | News

For internal combustion engines, which use electric sparks from spark plugs to burn the air mixture in the combustion chamber, it is important to know when to ignite the spark plug.
Although non-contact ignition is the norm today, before 1980, point ignition, which mechanically opens and closes the contact points, was common from mopeds to heavy-duty vehicles. This adjustment is very important because the slightest adjustment can greatly change the feeling of the ignition.

Ignition timing is extremely important for internal combustion engines

The good mixture,” “good compression,” and “good spark” are three elements that have remained unchanged and important ever since the gasoline engine (internal combustion engine) first appeared in this world. Point ignition, which was used in motorcycles and automobiles in the past, has disappeared and full transistor ignition with no contact points is now mainstream, but the fact that the spark plug is operated by sending sparks to the spark plug itself is no different.

Regardless of whether it is a mechanical point of contact or no point of contact, the ignition timing of when to let off the spark is important for the engine. By igniting with a spark at just the right moment in the process of the piston, which is rising in the cylinder after inhaling the air mixture, reaching its top dead center, the piston can be pushed down with maximum force as it begins its descent beyond the top dead center. Generally, the ignition timing is set before the top dead center. If the ignition timing is set too early, the combustion pressure becomes a force that pushes back the piston in its upward process, and if the ignition is set after the top dead center when the piston is descending due to crankshaft inertia, the explosive pressure cannot be effectively utilized.

In point ignition engines, sparks fly to the spark plugs the moment the contact breaker contacts open, so adjusting the spark plugs is an important maintenance item. On the other hand, transistor ignition and CDI ignition have no contact points and are therefore maintenance-free. However, the concept of ignition timing is just as important as in point ignition cars.
Rather, the recent digitally controlled full-transistor control system has multiple pulse-rotor triggers (protrusions) to detect ignition timing, which makes it easier than point-ignition cars, which have a single contact that opens and closes once per crankshaft revolution, or early full-transistor ignition cars, which had only one trigger. The feature of this system is that the ignition timing can be changed finely according to the engine speed and load. In other words, ignition timing is as important as ever even for a high-performance engine, and conversely, the ability to adjust ignition timing finely and appropriately according to driving conditions enables stable and high performance.

Although the contact breaker of an old or out-of-print car looks very old-fashioned, it should be noted that it is an important part that is no different from a modern digital ignition system in terms of sending a spark to the spark plug at the right moment.

It is important to precisely match the moment when the contact point opens.

Point ignition vehicles cut the primary current flowing to the ignition coil by opening the contact breaker contacts, and the self-induction action of the coil that occurs during this process generates a high voltage. Therefore, the most important factor in adjusting the ignition timing for “good ignition” is to match the position of the piston in the cylinder = crankshaft angle (or camshaft angle, depending on the engine) and the timing of the contact breaker opening as close as possible. In addition, the gap when the contact point opens (point gap) is also important, but here we will focus only on ignition timing.

The contacts of the contact breaker open and close with a point cam, and the primary current is cut off at the moment they open, but it takes some experience to determine the “moment” they open. While staring at the contacts, turn the crankshaft (flywheel) slowly in the forward direction (direction of engine rotation), and when the contacts begin to move slightly, that is the ignition timing. For engines with T (top dead center) and F (ignition timing) marks on the outer circumference of the flywheel, you can use these marks as a reference, but even if the ignition timing is perfectly correct, the movement of the contacts can be so delicate that you may wonder, “Did it really just start opening? The movement of the contact points is so delicate that even if the ignition timing is perfectly correct, the engine may not be able to open.

When you hear the word “open”, you may think of a contact point that is completely open to the point where there is a gap, but the actual change is extremely small. The actual change is extremely small. The actual change is about the same. Even if the change is so slight that it cannot be seen visually, it is important to accurately detect the slightest change in the electrical flow of the ignition system, because the primary current is interrupted and sparks fly from the ignition coil when the perfectly closed contact point opens, even if only slightly.
This is why there is an F-mark on the flywheel, but as mentioned earlier, there is sometimes too little movement of the contacts at the F-mark, making it difficult to adjust the timing.
In such cases, a small bulb can be used to adjust the timing.

Preparation is as follows:
Unplug the terminal leading from the contact breaker to the ignition coil, connect the terminal on the contact breaker side to the 6V battery and the 6V bulb, and ground the wire on the other side of the bulb to the frame.
When the flywheel is turned in this state, the bulb will glow brightly while the contacts are closed, but will dim slightly the moment the contacts are opened. You can tell by checking the timing of the dimming of the bulb and the state of the contacts at the same time, but the bulb will suddenly dim at a time when you cannot tell if the contacts have opened or not.
If the F mark on the flywheel matches the matching mark on the engine side at the time when the bulb dims, the ignition timing is normal.
If not, the breaker plate is fine-tuned so that the bulb dims at the F-mark.
This is a primitive method that has been used since the 1960s, but it is still valid today in terms of accuracy.
However, this adjustment is also delicate, and even a slight movement of the plate may cause a significant shift in the ignition timing. Nevertheless, we patiently make the adjustment, and when the timing of the dimming of the bulb and the F mark is perfectly aligned, we tighten the breaker fixing screws firmly.

On the other hand, one method is to visually check the timing of the opening of the contacts, start the engine, illuminate the timing light, and adjust the timing if it is off from the F mark, but it is troublesome to start and stop the engine each time to check the adjustment. Also, in the case of a 4-cylinder car, the ignition timing adjustment must also be done at two points because the No. 1/4 and No. 2/3 plugs are managed by two contact breakers. If either of these points is out of the proper position at that time, the engine may not start. To prevent this, visual + bulb adjustment is effective. If the ignition timing is precisely adjusted before starting the engine, the possibility of starting difficulties due to this can be greatly reduced.

Even with such careful adjustment, point ignition cars still have some elements that change over time, such as friction between the point cam and heel and contact point burnout, which is why they have been replaced by non-contact transistor ignition systems. It is not correct to shelve poor adjustment and lack of maintenance and unilaterally deny point ignition.
The first step is to try to adjust the ignition in a simple but rational way to obtain the “good spark” necessary for the engine.

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