Distributor - Breaker Points

[NickyHansard]

I'm just wondering if somebody can clear up what and why distributors need breaker points. I understand that it is necessary to drop the voltage to the outer coil, which produces a magnetic field due to the different lengths of the coils so the inner coil can create a large voltage spike. How do systems that don't contain the contact breaker work? What about when you move the position of the distributor cap, does it also move the position of the breaker points? Thanks for your help.

[shorod]

Welcome to the forum!

Depending one what you intended by a few terms, it sounds like you have a pretty good understanding of how the points work.

You say, "I understand that it is necessary to drop the voltage to the outer coil". If by "drop the voltage" you mean "open the points to collapse the field" and by "outer coil" you mean "secondary winding", that's what the points are doing. There is often a dropping resistor that is there to lower the voltage to the coil and help protect the points, along with the condensor (capacitor).

The coil is an autotransformer that, depending on the turns ratio, steps up in this case the primary voltage (usually 6 or 12 voltage) to a much higher voltage (usually in the 25,000 volt range) based on the ratio of turns of the secondary winding to the number of turns of the primary winding. When the points are closed, the coil is allowed to "charge up" the magnetic field. However, once the points open, the field collapses and discharges through the gap of the spark plug, igniting the air/fuel mixture when everything is in time and compression is good.

The breaker is essentially just a switch. Now days the function of a switch is typically performed through the use of a solid state (no moving parts to wear out) transistor. The transistor could be a Bipolar Junction Transistor (BJT) or now the lower loss, faster Field Effect Transistor (FET). Transistors are easier to control by and faster to respond to the PCM for timing and duration (pulse width) so they work great to enable much tighter emissions standards. Add to that the individual Coil on Plug (CoP) ignition systems and multi-point fuel injection, and all of a sudden PCMs can control fuel, spark, and timing VERY accurately just by altering when they open or close transistors and for how long they keep them open or closed for both the fuel injectors and coils, thus closely controlling the ignition timing. Many modern cars even are able to adjust the valve timing through adjustable camshafts.

Breaker style ignition systems were being phased out by the time I started helping Dad work on cars, so we'll need some input from someone else to clarify how the timing of a breaker style ignition system works. My suspicion though is that only the cap moves when manually adjusting the timing. That would adjust when the tower of the cap for each of the spark plug wires makes contact with the coil spark, therefore advancing or retarding the timing. The vacuum advance motor would be connected to the points though so it can independently advance or retard timing based on how far the vacuum allows the vacuum advance motor to move.

-Rod

[oldblu65]

Originally Posted by shorod

Welcome to the forum!

Depending one what you intended by a few terms, it sounds like you have a pretty good understanding of how the points work.

You say, "I understand that it is necessary to drop the voltage to the outer coil". If by "drop the voltage" you mean "open the points to collapse the field" and by "outer coil" you mean "secondary winding", that's what the points are doing. There is often a dropping resistor that is there to lower the voltage to the coil and help protect the points, along with the condensor (capacitor).

The coil is an autotransformer that, depending on the turns ratio, steps up in this case the primary voltage (usually 6 or 12 voltage) to a much higher voltage (usually in the 25,000 volt range) based on the ratio of turns of the secondary winding to the number of turns of the primary winding. When the points are closed, the coil is allowed to "charge up" the magnetic field. However, once the points open, the field collapses and discharges through the gap of the spark plug, igniting the air/fuel mixture when everything is in time and compression is good.

The breaker is essentially just a switch. Now days the function of a switch is typically performed through the use of a solid state (no moving parts to wear out) transistor. The transistor could be a Bipolar Junction Transistor (BJT) or now the lower loss, faster Field Effect Transistor (FET). Transistors are easier to control by and faster to respond to the PCM for timing and duration (pulse width) so they work great to enable much tighter emissions standards. Add to that the individual Coil on Plug (CoP) ignition systems and multi-point fuel injection, and all of a sudden PCMs can control fuel, spark, and timing VERY accurately just by altering when they open or close transistors and for how long they keep them open or closed for both the fuel injectors and coils, thus closely controlling the ignition timing. Many modern cars even are able to adjust the valve timing through adjustable camshafts.

Breaker style ignition systems were being phased out by the time I started helping Dad work on cars, so we'll need some input from someone else to clarify how the timing of a breaker style ignition system works. My suspicion though is that only the cap moves when manually adjusting the timing. That would adjust when the tower of the cap for each of the spark plug wires makes contact with the coil spark, therefore advancing or retarding the timing. The vacuum advance motor would be connected to the points though so it can independently advance or retard timing based on how far the vacuum allows the vacuum advance motor to move.

-Rod

Actually , the entire distributor housing is rotated to change the timing .This being done while the distributor shaft stays in it's relative position and this allows the timing to be advanced or retarded . This is done with the engine running and using a timing light and referencing timing marks usually found on the harmonic balancer . I have to add here that once the timing is set to it's initial setting , the distributor is locked in place by a bolt at the base of the housing . All timing changes after that take place inside the distributor . The distributor cap is clipped or bolted in place and moves with the distributor body .The vacuum advance is attached to the plate where the points are mounted and timing is advanced as the RPM's are increased and goes back to it's initial setting as RPM's go back to an idle . . These distributors also featured a centrifugal advance that was accomplished by way of weights and springs attached to the base of the point mounting plate that would change timing depending upon engine RPM's . Not sure my explanation is detailed enough to be understandable but hopefully it is ? Try going to this site as it explains it better than I ever could ! http://gasengine.farmcollector.com/g...n-systems.aspx

[oldblu65]

A second website showing photos and may better show the components of the point breaker style distributor and shows how they fit together . www.classictrucks.com/tech/0909clt_spark_plug_ignition_system_basics/photo_09.html

[shorod]

Originally Posted by oldblu65

Actually , the entire distributor housing is rotated to change the timing .This being done while the distributor shaft stays in it's relative position and this allows the timing to be advanced or retarded.

Ahh, right, I remember the bold and holding plate at the base of the distributor now that you mention it. Since the distributor assembly is rotate, it changes the spark position relative to the camshaft.

-Rod