Points Ignition Theory

[Crossrodes]

I am in the process of static timing my engine.  I was following the Clymer manual but it didn't seem to be working for me.  So I started to think about it.  I am using an Ohmmeter to check the continuity instead of the buzz box or continuity checker Clymer talks about.  What they say in the Clymer manual seems backwards to me so let me tell you how I think this works and you can either agree with me or correct me.

As I remember it the way points ignition works is that the points remain closed to allow 12 volts to get to the condenser.  When it is time for the plugs to fire the points open and cause the condenser to fire through the coil which in turn fires the plug(s).  So at the timing mark the points should be open and there should be no continuity through the points at that time.  Is this correct?  My Clymer manual seems to be saying the opposite to this.

[Justin B.]

When the points are closed the voltage flows through the primary winding in the coil generating a magnetic field.  When the points open the circuit is broken, the magnetic field collapses, and the "lines of magnetic force" cut back through the coil windings generating high voltage through the secondary windings.

Static timing is sort of a waste of time, just put the timing light on it...

[Semper Gumby]

I've never used an Ohm meter for timing.  I have a 12 volt light with two alligator clips.

One clip goes on the case and one clip goes on the bent spring of the points.

But first set the points cam on the highest part of the timing lobe.  Set the points gap to .016".  Then turn the crank shaft until the slow mark appears in the timing window next to the notch in the case.  Turn on the ignition on and go back to the ignition can.  Twist the can until the light just goes out.  

Tighten down the can crank the bike and put a strobe on the window and see how far off you are.  Go back and turn the can the direction you want the mark to move.  Simple !

Good luck.  If this is wrong then it's my bad.  I haven't done the points on a BMW since 2006 as I have the Omega ignition.  

But I did the points on my 1971 BSA Thunderbolt tonight and they came out purrrrrfect after doing just the static timing with a simple 12 volt light bulb.  The strobe confirmed my good fortune.   8-)

Remember to put a bit of grease on the timing lobe and on the plain bearing on the piece you removed off the top of the can to get to the points.  Otherwise it will sound like an angry mouse in about 3-5000 miles.

The theory behind the "buzz-Box" and the 12volt light is while the points are open, system voltage takes the path to ground through the light.  When the points close the system voltage bypass the resistance of the light bulb and goes directly to ground through the points -- the path of least resistance.  I don't know if there is enough resistance in your ohmmeter to cause the same effect.  But then I haven't tried it.

[Crossrodes]

Thanks guys.  Justin I'm doing the timing statically because I still have the gas tank pickling in vinegar.  Also I'm waiting for the POR-15 to be delivered.  I figured I might as well get this job done while I'm waiting.

[Barry]

Static timing with an ohm meter to detect when the points open works just fine as long as you know the advance mechanism is not worn.

I know from experience that I can set the timing very accurately with an ohm meter or buzzer and a subsequent check with the strobe will confirm it's Ok.

Why not use the strobe in the first place ?

Because I might not want to start the engine unless I know I'm going to use the bike and warm it up properly and I wouldn't strobe a cold engine anyway.

And if that is not enough heresy on the subject the truth is that unless you are close to pinging; ignition timing is just not that critical to the nearest degree.

[zebedee]

Why not use the strobe in the first place ?

Because I might not want to start the engine unless I know I'm going to use the bike and warm it up properly and I wouldn't strobe a cold engine anyway.

If you've had things apart you need a method to get the timing close enough to be able to get things running!

My father taught me to use a cigarette paper or similar thin paper between the points to detect when they open. Once again, it will get you close enough.

The best thing about points ignition is that when the motor stops you know where to start looking.

[Barry]

If you've had things apart you need a method to get the timing close enough to be able to get things running!

Exactly.... and I always take the bean can off to set the points because its so much easier to do on the bench.

[Justin B.]

Mike, OK, I understand.  I think some people static time then immediately dynamic time.  In a normal maintenance situation static timing as redundant...