Points Ignition Systems

 

Points ignition systems

One of my visitors emailed  a question about a CB 100 Honda and how to time, the points ignition system.  I decided this is a valid tip for all vintage riders.

Jake Anderson wrote:
I am just starting a big project on a 1971 CB 100K1.  I tried starting it for giggles, and have no spark.  I have no idea how to set the points on this bike.  Any information would be appreciated.  I picked the bike up recently and completely stripped it to the frame.  I'm also looking for reasonable powdercoater.

Jake,
This is information many a vintage rider can use.  Thanks for the idea and looking forward to posting pictures.

  Ignition coils work off of the “electromagnetic" principle.  If you had the good fortune of participating in a science project at some point in your grade school experience about electromagnets, you may remember something like this.
If we wrapped a wire or around a large nail and connect the ends of the wire to a battery, we will witness the magnification of the nail.  As we connect the wire and disconnect the wire we would see the change in current being present or not.  This is exactly how a set of points in a “battery coil ignition system” works.  This is the system you have made reference to; it is also a system that is used frequently in vintage Hondas.
This system needs a set of points for two reasons.  First, how long we saturate (or charge) the secondary coil (plug wire) and at what time we release that charge (the spark).  Imagine the points as the person who is connecting the wire and disconnecting the wire to the battery.  The points are connected to the primary side of the coil as a “negative control switch” (control to the ground side of a circuit).  When the points are closed the current flowing through the primary side of the coil is charging the secondary coil.  When the points are opened the stored charge in the secondary side is released and sparks the plug.
Setting of these points is critical then to get as much of the charge to the secondary side of the coil and then opening them at just the right time.  This time relates directly to the position of the piston in the cylinder.
To set the timing correctly, we need to make sure the point gap is correct and that is done with a set of points that are aligned and surfaced well.  This is why a new set of points will give us the best results.  It is difficult at best to restore used points to an as new condition.  The points spec for this bike and many Hondas is 0.3 -- 0.4 mm or 0.012 -- 0.016 in.  This of course is measured with a feeler gauge.  When the points cam has opened the points to the widest position the cam will allow, the gap measurement is made.
Making sure that the points cam starts to open the points at the right time is the ignition timing, we are referring to.  This is done in many ways; the timing light is my favorite.  The points are mounted to a plate on the end of the cam for opening and closing the valves.  It is under a cover at the top of the cylinder head (sitting on the bike) left side.  It has two #2 Philips head screws in it (stock), that when removed you will see the plate and the points.  There are two #2 Philips head screws that hold the plate to the head and allow you to rotate it when loose.
At the bottom of the cylinder there is another plate that covers the rotor for the AC generator.  It will have two or three #3 Philips head concave screws.  These are best removed with a hand impact driver and a heavy ball peen hammer.  Be sure to use a #3 Philips head driver. After removing this cover, you will see some letters on the rotor.  The letter that indicates when our points should first open is an “F”.  It is not a “T”.  When the “F” aligns with the pointer on the rotor cover the timing light should illuminate.  This is with the ignition key on and the engine rotating.  The timing light also needs to be clamped to the spark plug wire.
A side note: the AC generator for this model has oil in its compartment.  When the engine is running with the AC generator cover removed, there will be a shower of oil.  You will need to have the bike upright and a container to catch the oil that may come out of the engine through this removed cover.  It will not be a lot.
I use the kick starter to turn the engine over slowly with ignition on to see if the timing light illuminates when the “F” mark aligns with the pointer on the AC cover.  If there is alignment, the timing is correct.  If the alignment is off, you must rotate the plate the points are bolted to.  This will change that alignment.  Turning it clockwise will advance the timing and counterclockwise retards the timing.  When it is in the correct position lock down the screws on the points plate and recheck.
The next step is to check the advance mechanism.  This mechanism is bolted to the end of the cam that controls the valves.  It also has the points cam on it.  It is behind the points plate.  It uses centrifugal force, and a set of weights and springs to control this advance mechanism.  As you accelerate the engine you will notice a line on the rotor with the no letter beside it aligns with the cover pointer.  This is the advanced timing mark.  If it aligns with the pointer the advance mechanism is working well.  If it does not the advance mechanism can be seized or the springs can be weak.  Replacing it is best but I have repaired these units.
A small dab of light grease on the points cam will lessen the wear on the points actuator block.  The condensers in the system are to eliminate spark across the points which aids in less wear across the points.   
This model relies on the cam chain to drive the points so make sure it is tight.  Any model motorcycle you may be working on that uses the cam to drive the points will need this cam chain tension matter addressed.  If the bike drives the points off of the crank; i.e. CB750 it is direct drive and is not of concern.

That brings up the dual point system of many metric models. The CB750 has dual points and everything still applies except there are 2 sets of points. On a lot of models this dual point system is for two cylinders. The old system on CB72 and CB77 with dual points had 2 sets of points one for each cylinder. Everything still applies but 2 items. Set the "left side" set of points to the "LF" mark on the flywheel and the "right side" set to the "RF" mark. Start with the left side and adjust by moving the points plate. Then the right side will be close but if not spot on adjust it by variance of the point gap. The new style dual points will have an extra plate on top of the base plate. It is so you can adjust the right point gap as it should be then move the second timing plate after adjusting the left side for timing. Then the left and right timing mark have a seperate advance mark. Some of the twin cylinder model will have oil and others will not. All four cylinder models are dry and timing marks are with the points plate at the crank.

Four cylinder models use one set of points for 2 cylinders. So timing the left side sets the timing for cylinders 1 and 4 the right side 2 and 3. This means you can not have a problem with the points or timing of cylinders on the same set of points. If the left points are firing cylinder #1 and you have a problem with #4 you can rule out the points gap and timing as the problem for #4.

These are general conditions. Many other models will have similarities in the procedure.  Finding where the points are, how they are driven and the timing marks that coordinate the ignition timing are what the differences in your procedure will be.
If you have a particular model that you may have questions about write me and I will attempt to help.

Here’s hoping to wave from the oncoming lane.

Ross