One of the requirements for a good spark, which is one of the conditions for a good engine, is that sparks must fly to the spark plug before the piston reaches its top dead center. Today's engines use electrical signals to make sparks fly, but until the mid-1970s, this was the norm until the mid-1970s, when it was done mechanically. We can understand how ignition works by understanding the mechanism known as the "contact point".
The modern ignition system just replaces mechanical operation with electricity!
The KZ900LTD is a derivative of the KZ900, the successor to the Kawasaki Z1/Z2. The contact breaker is located inside the point cover on the right side of the engine (the cover with the DOHC embossed on it); up to the KZ1000, the KZ1000Mk II uses point ignition, and the KZ1000Mk II uses full transistor ignition.
All fuel engines in motorcycles and cars are powered by electric sparks generated in the spark plugs that cause the mixture in the combustion chamber to explode, pushing the pistons down with the force of the mixture expanding all at once, whether it's the 3.7-hp Super Cub 50 or the 218-hp CBR1000RR-R. If sparks don't fly at the plug, the engine won't run.
The timing at which that spark is generated is also important. There is a general rule that the best time to ignite is just before the top dead center of compression. The moment when the piston is at the top of the cylinder with the intake and exhaust valves closed is called the upper dead point of compression, and just before the mixture is sealed in the combustion chamber, sparks are sent out to drive the pistons beyond the top of the cylinder into explosive combustion.
The contact breaker point (hereafter abbreviated to point) determines the timing of that ignition. Points were common on motorcycles and cars before the 1970s. But after the 1980s, they disappeared and are now replaced by non-contact ignition systems such as transistor and CDI types.
The reason why the old car was the point is that at the time there was no other mechanism to determine the exact ignition timing from a fast spinning engine. Later, as electronic components became smaller and more powerful, they were able to pick up the rotating signal electrically, and the point became obsolete.
However, even with modern motorcycles equipped with complex and sophisticated electronic control systems, the fundamental mechanism remains the same: the position of the pistons is calculated from the rotation of the crankshaft and camshaft and ignited at the optimum time. Therefore, if we can understand the function and maintenance of the point where the mechanical components are in full view, we can understand the ignition mechanism of the current car that has been replaced by a black box.
POINT
- Point 1 - Gasoline engines, old and new, combustion is caused by sparks in the spark plug.
- Point 2 - Ignite when the piston rises to its upper compression dead center
One rotation of the crankshaft opens the contacts once.
The vertical streaks in the inspection window are the alignment marks on the crankcase side, and the small "T" below the mark is the breaker base, where the "T" indicates the top of the piston. Since we have passed the "F" mark for ignition time, the point of contact is already open before the inspection window, and it is the point on the left that ignites the plugs 1 and 3.
The movement of the points is synchronized with the crankshaft (or camshaft for 4-strokes) because the spark plug is ignited when the piston is just before the top dead center of compression. The point interrupts electricity by opening and closing the contacts, and the moment the closed point opens, a high voltage flows from the ignition coil to the spark plug, creating a spark.
When the point opens and electricity flows, an electromagnetic induction effect occurs, but we won't go into this explanation. Just remember that sparks fly to the plug the moment the closed contact point opens, and that's it.
As a side note, the transistor type ignition has the same trick of generating high voltage from the ignition coil at the moment the electricity that was flowing is cut off, and the mechanical contacts are replaced with no contacts; the CDI type uses electricity in the opposite way, generating high voltage at the timing of the ignition timing to generate more voltage, and then the spark flies to the plug. The pressure is raised by the ignition coil.
The action of opening and closing the point contacts is done by the point cam on the breaker base and the heel on the point arm, which is located on the crankshaft (or camshaft). The oval-shaped cam has a mountain at one point, and when the heel rides up on this point, the contacts leave. I mentioned earlier that sparks will fly when the contacts open, but the best sparks will fly when they open at the right time depending on the position of the cam and heel.
Ignition timing varies from engine to engine, but in the case of the Kawasaki KZ900LTD (a successor and derivative of the Z1) shown here, it's 20 degrees before top dead center at 1500 rpm and 40 degrees at 2350 rpm. The reason why the ignition timing becomes earlier at idle as the engine RPM goes up is because the speed of the piston moves faster as the RPM rises and the timing of explosive combustion is relatively delayed if the engine continues to ignite near its top dead center.
To change the ignition timing as the engine rotates, point ignition uses a mechanical mechanism called a governor, which is activated by centrifugal force. The contactless transistor type uses an electrical signal to keep track of the engine speed and change the ignition timing electrically.
The threaded holes in the point base to which the contact breaker is attached are also long holes, so when the ignition timing cannot be adjusted with the contact breaker alone, the point base is shifted to adjust the ignition timing. When this point base is removed, there is a spark advancer that changes the ignition timing according to the engine's RPM. There is a camshaft that opens and closes the point at the center of this point.
POINT
- Point 1 - The contact breaker point is synchronized with the crankshaft or camshaft (in the case of 4-stroke engines).
- Point 2 - The higher the engine speed, the faster the ignition timing.
Contact breakers are adjusted by "maximum gap" and "timing".
The gap when the cam pushes the heel of the point arm and the contact is opened to its maximum is measured with a thickness gauge, and if it's not between 0.3 and 0.4 mm, the screw is loosened and adjusted. In the old days, it was said that if you didn't have a thickness gauge, you could use the thickness of a business card as a guide, but nowadays, there are many different types of business cards, so it's hard to rely on a general rule of thumb.
Rely on the alignment mark on the crankcase and the F stamp on the breaker base to match the timing of the contact breaker contacts opening. From the right side of the engine, the crankshaft turns clockwise, but if you turn it backwards slightly before and after the F mark, you can see the slight movement of the contacts before and after the opening and closing of the crankcase. Do not turn it too far because it will cause strain inside the engine.
Ignition is provided by a set of lid points on a four-cylinder engine with a point system, including the KZ900LTD that appears here. This is due to the fact that pistons 1 and 4 and pistons 2 and 3 are in the same position, each 180 degrees off from the other.
In other words, pistons 1 and 4 are firing at the same time, and pistons 2 and 3 are also firing at the same time. For this reason, the two points must be checked separately when adjusting the ignition timing.
The contact breaker points are adjusted by two items: "Maximum Gap" and "Ignition Timing". The maximum gap is the gap where the point contact is opened to the maximum, and it is specified at about 0.3-0.4mm, not only for the KZ900LTD but also for the KZ900LTD. The point contact opens when the heel of the point arm is on the cam mountain of the breaker base, and the gap width determines how long the contact is open.
If the gap is narrower than the specified value, the time that the contacts are closed is longer, and sparks will try to fly between the contacts when they are farther apart, causing the points to burn faster. On the other hand, if the gap is wider than the specified value, the time that the contacts are closed is shortened, so there is not enough current flowing to the ignition coil to weaken the sparks.
Therefore, use a spectacle wrench to turn the crankshaft with a spectacle wrench to measure the maximum gap with the heel of the point arm on the apex of the cam mountain and adjust it if necessary. However, the heel, which is in constant contact with the rotating cam, wears out and may not be able to be adjusted fully as the mileage increases. In this case, the contact breaker itself needs to be replaced.
Next, the contact breaker itself needs to be adjusted so that the point contacts open at the moment when the alignment mark on the crankcase and the "F" mark on the breaker base, which indicates the position of the cam mountain, match. The breaker base and the contact breaker are paired with pistons #1 and #4 and #2 and #3, so adjust them separately.
As you move the crankshaft forward and reverse within a narrow range before and after the "F" mark, you'll get used to it and you'll be able to visually judge the moment when the F mark and contact points open. However, it can be fuzzy due to cam and heel friction, so use the timing light to determine it accurately.
To check the ignition timing for numbers 1 and 4, attach the timing light cord to either the number 1 or 4 plug cord, start the engine, and illuminate the alignment mark on the crankcase. The timing light will strobe light at the same time as the spark plug ignites, so if the adjustment is correct, you should see the F mark on the breaker base stop at the alignment mark position.
If both marks are not aligned at this point, stop the engine and readjust the contact breaker position. You can tell if the ignition timing is off in the forward or delayed direction by illuminating it with the timing light, and you should be able to adjust it according to the results to match the correct ignition timing.
If the ignition timing is not correct, the mixture will not ignite at just the right time, which can lead to insufficient horsepower, knocking, poor acceleration and overheating. This is a task that is completely unfamiliar to non-contact transistorized or CDI mootorcycles, but knowing the procedure for adjusting the point ignition will help you understand how ignition to the spark plugs works.
If you own a point-ignition bike, you'll want to have a timing light. There are several products available, including battery-operated and 12-volt battery-powered, as well as high-performance products with tachometer functions.
Even at idle, the breaker base spins too fast to read the imprint, but when you shine the timing light on it, the strobe light flashes as electricity flows through the spark plugs, so the tick lines and letters appear to stop, and the F tick line between 1 and 4 matches the matching mark on the engine side So we can judge that the ignition time of No. 1 and 4 is right.
POINT
- Point 1 - The contact breaker adjusts the point gap and ignition timing.
- Point 2 - The timing light is necessary to confirm the correct ignition timing.
