A simple and basic ignition system in the 1970s = how to maintain a contact breaker

How to

The three main prerequisites for all engines are: good mixture, good compression and good spark.
As for the spark, today only non-contact types are available, but until the 1970s, mechanical point-of-contact types were the norm and required regular adjustments.

Igniting the plug at the right time leads to a good spark, whether it is contact or non-contact type.
Riders interested in out-of-print or older cars can benefit from knowing about point maintenance.

How do you decide when to ignite it?

The model used as a sample is a 1970s Yamaha Chapie. The engine is a two-stroke engine, and before the advent of the scooter, it was a favorite family motorcycle used for commuting to school. . Later models will have non-contact CDI ignition, while early to mid-term models use point ignition.

The spark plug ignites the compressed air mixture in the combustion chamber to cause explosive combustion. This is the principle of the internal combustion engine. A mixture of air and gasoline, through a mixture of air and gasoline, compression as the piston rises in the cylinder, and finally The engine will perform as it should when the ignition that triggers the combustion is aligned with

On the flip side, if any one of these three elements is missing, the engine will not perform as well as it should. That's true whether it's an older car from the 1960s or a newer model in 2020. If you look at ignition, modern motorcycles have a computer in combination with injection to create a mixture of air, and the computer It's a controlled, non-contact type, and doesn't require the bike owner to do any routine maintenance No. At best, you will have to change the plugs.

However, this is not the case with the point-type ignition that many bikes built before the 1970s use.

The timing of plug ignition = ignition timing depends on the type and specifications of the engine and the RPMs used. In the case of a 4-stroke engine, the intake and exhaust valves are both closed and The piston ignites just before the compression top dead center, where the piston reaches its top dead center, and the piston crosses the top dead center and As it begins to drop, an explosive combustion occurs, which can push the pistons down with great force.

This ignition timing is based on the angle of the crankshaft for a four-stroke engine, and the top death for a two-stroke engine. It is usually indicated by the piston position down in front of you from the point. Earlier or later than the correct position, the mixture will not ignite properly. Modern contactless ignition has no mechanical element and therefore does not cause the ignition timing to shift in the process of use. On the other hand, contact point ignition, which mechanically determines the ignition timing, is not affected by wear and tear. This can change and requires regular checks and maintenance.


  • Before the 1970s, point-type ignition was common
  • Point system requires regular maintenance

The construction of a contact breaker is surprisingly simple

The brown part is the Bakelite point heel. One of them makes contact with the point cam and the other is a contact that interrupts the electricity flowing to the ignition coil and The spark that occurs when the point contact is opened is suppressed by a separate capacitor. The spark that occurs at the moment the point contact opens is suppressed by a separate capacitor.

The point that is the main role of the point ignition is also called the contact breaker, and the crank The point cam, which rotates in conjunction with the shaft, opens the point once per revolution of the crank. It creates a spark in the plug. So the points are only open at ignition timing and closed the rest of the time.

To open and close the points, the point heel is in contact with the cam. This heel is made of a plastic material called Bakelite, and rotating in contact with the point cam. It will gradually wear out at the end of the day. Then the timing of the points opening will be off, and the engine will not be in tune. Also, the surface of the point contact, which interrupts the electricity flowing to the ignition coil, will be worn away as it opens and closes. It can be rough and affect the ignition.

When you write this, you might think of a high-tech, challenging system. The contact breaker is an extremely analogue mechanism. This is why they have been replaced by the contactless type in later times.

So, once you understand the theory and get to the point, daily maintenance is not too difficult. . Rather, because there is no electrical circuitry = black box like CDI ignition or transistor ignition, there is no mechanical In some respects, it is easy to understand because the target maintenance works.

The gist of it is to position the contact breaker so that when the crankshaft reaches a defined ignition time, the point is open.

The moment the markings on the flywheel and the contact breaker side meet, the point is opened. Adjust the position of the contact breaker. The angle of the contact breaker can be adjusted by the length of the contact breaker hole.


  • The point opens once per revolution of the crankshaft.
  • Wear on the mechanical contact area affects the ignition timing.

Point-of-use maintenance

Right is a contact breaker and left is a condenser. Some models are supplied with original manufacturer's parts, but even if they are no longer sold, external parts are available. This part is not a genuine part, but is made by a third party. This part is not a genuine part, but is made by a third party.

I matched the ignition timing with the point cam and point heel position and the point opened up. The gap = point gap is measured with a thickness gauge. If the gap is specified for a model, it is adjusted to the specified gap, but the type of contact breaker Some models allow only the ignition timing to be adjusted, but not the gap.

The 1970s moped 2-stroke model I used as a sample car had a contact breaker. It is assembled on the inside of the flywheel. There is an eccentric cam in the center of the inside of the flywheel that contacts the point heel.

The contact breaker itself is not visible, so it's hard to understand how it works, but many fly There is a mark on the wheel to indicate ignition timing. Also, the screw holes of the contact breaker are long holes, so that it can be installed in the base plate. The angle of the flywheel can be adjusted within a certain range. Adjust the point to open the moment the mark matches the mark on the flywheel.

It takes some experience to determine the moment when the cam mountain pushes up the point heel and the point opens, but by turning the crankshaft a few times and observing the point opening and closing, you'll be able to tell when the contacts start to open.

Once the manual adjustment has been made to determine the ignition timing, check to see if the engine engages and revs rise smoothly, and if there are no problems, the job is done.

If the ignition timing can't be adjusted due to point heel wear, or if the contacts are rough and not sticking together, remove the contact breaker and check, but an engine built inside the flywheel will require a separate flywheel puller to remove the flywheel.

In addition, if you have a tester called a timing light, you can check the ignition timing with the engine running, which is more accurate than adjusting the markings while the engine is still running.

Remembering the once-popular point-ignition maintenance, from mopeds to the 750cc class, may be helpful for the opportunity to get to know your old or out-of-print car.

If you have a timing light, make sure the points are opened and closed correctly with the engine running. You can do this. The strobe light of the strobe unit fires when current flows through the plug cord. Due to the high response, the marks stop when the flywheel and contact breaker are illuminated. It looks like.


  • Determine when the point cams push the heels.
  • Some models have a contact breaker on the inside of the flywheel.

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