What Happens to the Engine When the Condenser in the Set Malfunctions with the Contact Breaker? | Necessities for Point Ignition

In the contact type ignition using contact breaker, which has become extinct in current motorcycles but is familiar to users of out-of-print motorcycles, the condenser is doing an important job along with the points in order to send sparks to the spark plug at the moment when the ignition timing is reached. In the maintenance of contact ignition, we tend to focus on the contact breaker, but it is also important to understand the role of the condenser, which is a small round tube.

Spark plugs with two types of "induction" to make sparks ignite

If a contact breaker is installed on the end of the crankshaft, it is often set inside the flywheel. The sample vehicle is Yamaha's family motorcycle, Chappy. After removing the center lock nut, screw in the special tool, flywheel puller, and pull it out to the front.

The two sets of coils lined up on the contact base inside the flywheel, one is the power generation coil for ignition (sometimes called the source coil or charge coil) and the other is the coil that charges the battery. The cylindrical component that looks like a dry cell is the capacitor.

The voltage of the battery is 12V (some older motorcycles also have 6V), so if you accidentally short the terminals, you may be surprised by the sparks. If you accidentally short the terminals, you may be surprised by the sparks that ignite. Similarly, the spark plug installed in the engine triggers combustion by sending electric sparks to the air mixture in the combustion chamber. However, unlike a battery short that sparks by accidental contact with a tool, the spark plug must continue to send out sparks at the correct timing every time it ignites the mixture. For example, when the engine is rotating at 6,000 rpm, the crankshaft is turning 6,000 times in one minute, or 100 times in one second. And in the case of a points ignition vehicle, if it is a two-stroke engine where the points are opened and closed by the crankshaft, the points are opened and closed 100 times in one second.

However, the engine does not work because the mixture is burned even outside the ignition timing before the top dead center by the continuous fire like a lighter or a burner. It is necessary to ignite the spark to the spark plug intermittently by opening and closing.

The ignition coil generates the 20,000 to 30,000V voltage needed to spark the spark plug against the contact breaker that opens and closes at such a furious rate. Mopeds and small-displacement motorcycles use the source coil in the flywheel magneto as their power source, while mid-sized motorcycles and larger use the battery as their power source, but the original voltage of both is not far from 20,000 to 30,000V. The ignition coil contains two types of coils, a primary coil and a secondary coil, and this is where the voltage is boosted. The principle used in this process is the action of coil self-induction and mutual induction. This action, which is taught in high school physics, is connected to difficult subjects such as Lenz's law and Faraday's law, and is also utilized in the ignition system of motorcycles.

To summarize the two actions, the primary coil's self-induction attempts to cancel out the magnetic field generated by changing the current flowing in the coil, and the secondary coil's mutual induction creates a magnetic field that interferes with the change in the magnetic field generated by self-induction. There are some parts that are difficult to understand even after summarizing, but in order to generate self-induction in the primary coil, it is important to quickly cut off the change in the current flow. By cutting off the current as if you were turning off a switch, rather than gradually reducing the current as if you were turning down a volume, the change in the magnetic field generated in the primary coil will become larger, and the mutual induction in the secondary coil will work proportionally larger, and the voltage flowing to the spark plug will become higher.

The self-induction of the primary coil is determined by the immediate breaking of the current

The one on the right is a new one while the one on the left is a used one, but they look almost identical because they don't have any moving or worn parts like contact breakers. Inside the capacitor, there are two metal plates facing each other with air and insulators in between, which can store and release electricity. When the insulator deteriorates or the metal plates inside short out due to overvoltage, a puncture occurs and electricity cannot flow in or out.

If the condenser is broken, the current flowing in the primary coil of the ignition coil cannot be cut off at once because the conduction is continued by the discharge when the contact of the contact breaker is opened. Therefore, the self-induction action of the primary coil and the mutual induction action of the secondary coil do not occur as ideal, and the spark generated in the spark plug becomes small or becomes a cause of loss of fire. The condenser is effective in preventing burnout of the point contact, but its main purpose is to instantaneously interrupt the primary coil current.

While the points are closed, current flows through the primary coil and a magnetic field is generated, and the moment the points are opened and the current to the coil is cut off, self-induction occurs to maintain the magnetic field that had been generated until then, and a large voltage is generated in the secondary coil by mutual induction. I have explained it in a complicated way. The contact breaker is a component that interrupts the current flowing in the primary coil at the correct time.

When the points open slowly, the current flowing in the primary coil decreases gradually, so the change in the magnetic field becomes gentle, and the voltage applied to the spark plug also becomes small because the mutual induction to the secondary coil becomes small, leading to the result that a large ignition spark cannot be obtained. On the other hand, if the points are momentarily opened and the current is momentarily cut off, the current due to self-induction increases in the primary coil, and mutual induction in the secondary coil also increases, resulting in a large voltage being applied to the spark plug.

If you observe the contact breaker that opens and closes in conjunction with the rotation of the crankshaft and camshaft, you will not be able to follow the opening and closing of the points with your eyes as the engine speed increases. Even in such a situation, the point heel and the point cam are in contact with each other and open and close exactly, so the mixture is burned correctly and the engine can perform.

However, for the contact breaker, which has mechanical contact points, such as the point where electricity is cut off and the contact area between the point cam and the point heel, changes over time due to wear are inevitable. Also, as the engine speed rises, there is a limit to the mechanical opening and closing. For these reasons, and due to the spread of semiconductors, the non-contact transistor ignition, which electrically interrupts the current to the primary coil, came to the fore. The ignition systems of today's motorcycles are now all contactless, eliminating the need for points maintenance.

The capacitor absorbs the leakage current that tries to flow to the point

Some types of condensers have a felt holder integrated into the stay. By soaking the felt with an appropriate amount of oil and keeping it in contact with the point cam, lubrication between the cam and point heel is ensured and heel wear is prevented. It is necessary to check the oil periodically so that it does not become depleted.

When replacing a damaged condenser, select a product of the same capacity and fix the wiring with solder. Although various products are available on the market as electronic parts, it is safe to select a condenser sold as motorcycle parts when it is used as a contact breaker for a motorcycle.

The contact breaker points open to interrupt the current to the primary coil. Condensers with important and essential components for contact ignition systems connected in parallel with the points. It is important to open the points quickly in order to generate a large spark on the spark plug. It is important to open the points quickly in order to make a large spark ignite in the spark plug, but there is a lapse of time, although it is a very short time, from the start of opening until the points are completely open, and during this time the electric current tries to continue to flow. Since the electrical resistance in the air is very large, electricity will not flow through the gap between the points when they are completely open, but sparks will be generated as electrical sparks while the points are opening.

Electric sparks are a major factor in burning out the point contacts, but at the same time they interfere with the interruption of current to the primary coil. Even if the points appear to open with a bang, while a small amount of current is flowing between the points, no large self-induction occurs in the primary coil, so the spark of the spark plug does not become large. It is the capacitor that does the important work here. The capacitor stores and releases electricity, and when viewed on its own, it behaves like a rechargeable battery. However, unlike batteries, capacitors have an extremely good charge-discharge response, and their ability to react sharply to small changes in current is a major feature.

By placing the capacitor in parallel with the points, the moment the points begin to open and a small gap is created between the closely contacted points, the electricity that is no longer flowing easily is used to charge the capacitor!. It is easier for the electricity flowing to the points to flow to the condenser than to discharge the gap between the points = less resistance and smoother, and as a result, the current between the points can be cut off quickly, and the self-induction and mutual induction of the ignition coil can be drawn out greatly. At the same time, the reduction of sparks between the points also reduces the burnout of the point contacts, so it is really killing two birds with one stone.

Capacitors are used in all kinds of electrical products, not just motorcycle contact breakers, due to their function. And although a capacitor by itself has no contacts or electrical circuits, it has an intrinsic life span and will not be able to perform at its full potential due to aging and other factors. The amount of electricity that can be stored in the capacitor is determined for each product, and if the capacity decreases or cannot be stored at all due to deterioration or damage, the primary current will remain between the point contacts as explained earlier, and the interruption of the current to the primary coil will not be successful. If the capacity of the capacitor is reduced, a certain amount of the primary current can be charged and the current trying to flow through the points may be reduced to some extent.

However, when a puncture occurs completely and electricity cannot be accumulated at all, the self-induction action of the primary coil becomes incomplete due to the weak current flowing between the contacts even after the points are opened, and the mutual induction action that should occur in the secondary coil also becomes incomplete, and the voltage cannot be raised to the 20,000 to 30,000 V required for spark generation of the spark plug. This is the so-called lost fire. This is the so-called loss of fire.

When there is no problem in the ignition timing or the gap of the points, and there is no burnout of the point contact, but the engine does not blow up well, or when the engine does not start, the condenser might be ruined. A special tester is necessary to measure the condition of the condenser, but this is not as common as the circuit tester to measure the resistance value in the resistance, so if possible, try to install a new condenser and check the ignition condition.

In a single cylinder engine, there is only one contact breaker and one condenser, but in a four-cylinder point motorcycle, there are two of each, and each of them is responsible for the ignition of No.1 and No.4, and No.2 and No.3, so if the ignition condition of No.1 and No.4 becomes bad, connect the condenser for No.2 and No.3 and see if the situation changes. It is checked whether the situation changes or not. If the bad cylinder of the ignition changes by this check, the suspicion to the condenser becomes strong. If the situation still does not change, there may be a cause in the ignition coil itself or the power supply to the coil.

Although the contact breaker is paid attention first in the ignition system maintenance of the point motorcycle, the condenser also works very importantly though it is modest. It is important to know the role of the condenser in the set with the point that interrupts the current to the primary coil, and to understand the function correctly so that an appropriate response can be taken at the time of trouble.