It occurs to me that today, with such wide-spread use of electronic ignition systems in our cars, there are still a few of us who use breaker point ignition systems. While they still exist, it might be a good idea to print up what this system does, how it works, and how to adjust it. There was a day when every kid had to know this stuff just to drive his Z.

1. WHAT IT DOES.

Simply put, "Breaker point ignition" is a system which allows the primary circuit of the ignition coil to close and open, or close and 'break'.

2. WHY WE NEED THAT.

The primary circuit in the coil runs 12volts of DC electrical current around the center "core" of the coil. The core is a series of iron rods wrapped in thousands of feet of thin electrical wire running lengthwise thru the center of the coil. The primary circuit runs thru hundreds of feet of thick electrical wire (called windings) which "coil" around the center core. Hence the name "coil".
When the circuit is closed, DC current runs thru these thick primary windings. Because these windings are all coiled in the same direction, this builds up an electromagnetic charge in the core and secondary windings which they are wrapped around. The longer the circuit remains closed (and the more windings used), the higher/stronger this electromagnetic charge builds up.
When the circuit is interrupted or "broken", the electromagnetic field collapses around the metal core. That induces a 20,000 - 60,000 volt ELECTRICAL PULSE within the core rods themselves, flowing from positive to negative.
In operation, the building up and collapsing of these electrical fields and this electromagnetic pulse last only milliseconds each time.
Altho there are no moving parts in a coil, electrical resistance generates great heat in this operation, so the insides of the coil are surrounded by a special oil which absorbs and transfers heat.

3. HOW WE USE this 20,000+ volt electrical pulse.

The high-tension electrical pulse the coil produces flows thru the SECONDARY IGNITION CIRCUIT. (It is the "zap" you feel if you somehow place yrslf btwn the coil and ground while the engine is turning over). We use a very thickly insulated wire (spark plug wire) to route this electrical impulse from the coil tower to the center of the distributor cap.

The distributor "distributes" this high-tension electrical pulse to each cylinder in turn, by spinning a rotor from one cap terminal ("pin") to the next. The distance btwn the end of the rotor and the cap terminals is very small, but a small spark is created each time the electrical pulse jumps across the gap, anyway. The smaller the gap, the smaller the spark, but each spark represents a very high electrical resistance which lowers the strength of the available electrical pulse.

At each distributor pin, we use another heavily insulated spark plug wire to route this impulse to a certain spark plug. The 60,000+ volt pulse wants to return to Ground ("-") and can't escape out of the plug wires, so it races to the plugs themselves.

When the electrical pulse reaches the (highly insulated porcelain or ceramic) spark plug, it finds an air gap at the end of it's travel. The body of the plug has held and insulated the Positive ("+") charge, but in order to reach the Negative ground of the spark plug electrode, the pulse has to jump across this open gap. That causes a spark ~ which was why we built the whole system in the first place.

4. DISTRIBUTOR CONTROLS IT ALL

Inside the distributor there is a set of 'breaker points'. They "break" the primary coil ignition circuit, which causes the electromagnetic field to collapse around the core, creating that strong electrical surge which we cause to jump across the sparkplug air gap and make a spark. You can think of the breaker points ("points") as an on-off switch capable of operating many thousands of times per minute.

The points rest against a hexagonal cam in the center shaft of the distributor. As the cam turns (as the distributor revolves) the points open and close 6 times each revolution.

Because the primary electrical circuit of the coil flows thru these points, the coil circuit is opened and closed 6 times for each distributor revolution. That creates 6 sparks each time the dizzy spins once.

So, the distributor interrupts the 12v DC coil primary circuit, then receives the strong 60,000+ volt secondary circuit electrical pulse from the coil into the center terminal of the distributor cap. As the rotor spins, it transfers this pulse to each pin in turn.

The "dizzy" not only receives the spark from the coil and distributes it to each cylinder, it also 'times' it to arrive at the right instant for proper engine performance under all load conditions.

The floor of the distributor twists a bit in either direction. As it moves, it affects when the spark reaches each spark plug. Spark advance depends upon manifold vacuum strength (adjusted by the vacuum dashpot) or engine speed (adjusted by centrifugal weights). The body of the distributor can also be adjusted by twisting it manually in its housing to allow spark to reach the cylinders before or after Top Dead Center of the compression stroke.

5. ADJUSTING THE POINT GAP

The breaker points hold two electrical charges; one cap is Positive, the other Negative (or ground). Electrons flow from one cap to the other when the points are closed and touching.

Because we depend upon these points to open/close the primary circuit of the coil to create a dependable spark at the correct instant, it's important for them to make a 'clean' break. One of the problems with arranging a clean break is that electricity tries to jump across the point gap as the points open. That would cause the coil not to function in a timely fashion, so we have to arrest the spark before it jumps the point gap.

The condenser (or capacitor) serves that function. This little silver canister acts as a temporary 'storage reservoir' for the small charge of electricity which would otherwise try to jump across the air gap as the points opened. Electricity is basically lazy, and any air gap presents a high electrical resistance which the electrons would rather not have to jump across if they had someplace "easier" to go. The capacitor provides an 'easier' place for the electrons to divert to as the points open. The small electrical charge which would have jumped the air gap instead diverts into the capacitor for a brief instant, each time the points open. The capacitor (condenser) then discharges back thru the points when the circuit closes again.
*(NOTE ~ if an engine stops with the points open, that isolates the capacitor and makes it impossible to discharge. A small electrical charge will remain stored in the capacitor. That means when you remove it and touch both the Negative body and Positive pigtail lead, your hand will complete the circuit and you will get a small 12v zap. The amount of current is measured in MircoFarads, so no damage will result, but it will get your full attention. Charge one up and toss it to your buddy sometime!)

So the air gap btwn the breaker points is a critical measurement. If it is too wide, the coil will not build up a sufficient magnetic field to create a good spark when the circuit is broken. If the air gap is too narrow, the electrons can more easily jump across the gap, thereby not interrupting the coil's primary circuit. So the width of the air gap btwn the breaker points is very important and must be set with some precision.

The breaker point adjusting screw allows you to widen or close the gap btwn the points. With the ignition OFF and the manual gearbox in 3rd or 4th gear, you can use the driver's side front wheel to rock the car back and forth until the cam opens the points to their greatest extent. At that point I set the handbrake so nothing changes.

Using a feeler gauge, set the points gap to the specifications for your Z's particular year by turning the adjusting screw (a tiny cam which moves the breaker plate) and retighten the set screw.

6. HOW OFTEN SHOULD I DO THIS?

The two ignition points resemble tiny hockey pucks which touch each other's flat sides to open and close the circuit. Each time they touch, current flows from one point to the other point. As long as they maintain the proper air gap between them and the condenser/capacitor remains functional, the points work as advertised.

But each time they touch and current flows btwn them, a tiny bit of material is carried from the center of one point and is deposited on the center of the other point. Over time, this material transfer actually changes the physical characteristics of the two points. Instead of looking like two hockey pucks, one point resembles a donut and the other resembles a thumbtack.

When that happens, it eventually becomes impossible for the two points to separate widely enough apart to allow a clean break. The capacitor can no longer prevent a spark across the air gap (because the thumbtack spike never gets far enough away from the donut hole) and the primary coil circuit fails to interrupt properly. As the points approach this condition, the engine will begin to run poorly, indicating the points need attention.

I had the habit of carrying an emory board (nail buffer) in my glovebox. When I felt the engine running rough I would drag the emory board btwn the points to file off the 'tack point' and allow the points to work for awhile longer. I also used it to clean the metal end of the rotor, which got funky after extended use.

New points and a condenser were only a few bucks back in the day and each time I replaced mine, I noticed the difference immediately.

7. INSTALLATION PROBLEMS

One of the most aggravating problems I had with the simple task of replacing my points and condenser was that the screw which held the condenser in place was so close to the inside wall of the distributor, it was nearly impossible to get a screwdriver in there to turn it. In 1974 there was not yet an invention called an Offset screwdriver, so I had my buddy heat and bend a tiny tweaker screwdriver, bent to a right angle at exactly the right length to allow me to turn that condenser screw 1/3 turn at a time. That screw driver lived in my glovebox beside my feeler gauges and emory board. By 1973 enough people had complained about this, to make Datsun mount the capacitor on the OUTSIDE of the distributor.

Also, the condenser pigtail had to remain perfectly isolated from everything else. if I made the mistake of allowing the condenser pigtail to touch any part other than it's insulated mount, it would short out the entire system and I wouldn't get any spark. This was aggravated by the fact that the pigtail itself was sort of 'horseshoe' shaped, and mounted on the insulated mount with the two prongs facing down. Tightening the screw to hold it in place had the effect of twisting the horseshoe, and if the little 'foot' of the horseshoe grounded against the distributor floor, nothing worked.

I invite input from all sources on this subject. Corrections are welcome.

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1970 240Z

Here's an example of the small sparks which occur inside the distributor cap. This is not a Datsun/Nissan, but the principal is the same

http://youtu.be/OSBS-s0XxkQ

As you can see, the pulse jumps the small air gap btwn the rotor and the distributor cap terminals, creating a spark. This serves no useful purpose and depreciates the value of the ignition pulse, but it's technically unavoidable while using distributors.

There have been many cases of cars with worn piston rings allowing blow-by of unburned fuel into the crankcase. As these gasoline vapors built up in the crankcase, some of them climbed the distributor shaft to be ignited by these sparks, causing actual engine explosions. That was one of the primary considerations in favor of adopting the positive crankcase ventilation systems of today.

And use of individual cylinder igniters rather than distributors eliminates this problem altogether.

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1970 240Z

Here are some fairly good SloMo examples of ignition inside a running engine. Please note when the spark occurs ~ several degrees of crankshaft rotation before the piston reaches top dead center. That timing will vary due to load demands on the engine.

Keep saying to yourself; INTAKE ~ COMPRESSION ~ (spark) POWER ~ EXHAUST.


http://youtu.be/DRSe33tXDu4

http://youtu.be/UvmBLqjaZxY

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1970 240Z

And if a picture is worth 1,000 words, a video is worth a whole chapter.

http://youtu.be/W94iksaQwUo

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1970 240Z

This is the video I watched when I wanted to learn about the ignition system but this thread goes into more details than the other guides/videos that ive looked at.

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71' 240Z: HLS3040666

Frank,

I always find myself reading your posts with a big smile on my ugly mug.

I too have kept the original distributor in my 71Z. I have alsways thought it to be a reliable ignition system as long as you changed the points regurlary.

John Bianchi actually gave me an extra breakerless distributor that he had. I contemplated installing it but after mulling it over for a few days, I decided to keep the original distributor. I returned it to John with my thanks, but something inside me said that this is one of those maintenance tasks that is vanishing from the car scene. I still like to perform this maintenance on my car if not "just for old times sake".I always keep an extra set of inition parts in my car and I can practically replace each piece with my eyes shut.

Two seasons ago, on our way back from the Darien Fall outing, Kevin McCarthy's brown Z and I were getting back on the Merrit Parkway to head back home. His car just quit and had to be towed home to Middlefield. And guess what! It was his aftermarket electronic ignition system that failed!!

I'm keeping the points!

Best Regards,

John

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John Kish
1971 240Z - original owner

When the electronic ignition modules quit, there is no warning.

I could always tell when my points needed attention.

In many ways, Z ignitions are like women.

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1970 240Z

Bravissimo!
I bet a lot of the guys here never had to work with a breaker points system and the joys of moisture in the air and condensation inside distributor caps.
Next ime you can enlighten us about magnetos.

Thank you.

It would take about a paragraph for me to explain what I know about magnetos, so I can do that today!

And YES! Condensation under the distributor cap! Been there, done that, donated a number of T shirts to fix that cause.

Also, Champion, AC or Autolite sparkplugs on a rainy day! (Actually, it didn't even have to be raining! The weatherman could simply *think* about rain, and my Z wouldn't start until I bought NGKs).

Sounds like you've been there, too

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1970 240Z

Not with the Z's but a lot of other POS cars over the years.