75-79 ignition system

[Whiskerfish]

Let me start off with a disclaimer. I am not an electrical engineer but I do have some formal electronics background. Some of this is simplified either because I do not understand it enough to fully explain it or I felt it was not critical to the system's theory to go into further. Anyway here is my take on the GL1000 Ignition system as I wrote it up for the presentation at Randakk's last Rally.

Overview

The GL1000 ignition system consists of many individual components that when working properly produce a spark that serves the function of igniting the fuel air mix in each cylinder at the optimum time to produce the maximum performance. The Stock system while adequate is very often accused of being underpowered or anemic compare to modern high-powered systems. The design is called by several names including a “Battery operated Ignition System” (a generic term for many of the Contact Breaker point designs) a Wasted Spark or Simultaneous Spark System. For our purposes I am going to attempt to explain this circuit and it’s parts as a simple DC circuit. Those of you with more knowledge will of course recognize it as an Inductive Resistive Capacitive (LRC) circuit with time factors and many many many more variables than I can explain!! So we will stick with the basic DC theory side of it. The stock ignition system consists of the following components each of which we will discuss in more detail below:

Contact Breaker Points
Advancer mechanism
Points Cam
Ignition Coils
Ballast Resistor
Capacitors (also called condensers)
High Tension (HT) Leads
Sparkplug Caps
Spark Plugs
Ignition and Start Switches


Component discussion

Contact Breaker Points, Points Cam, Advancer

The purpose of the Contact Breaker Points is to interrupt the current flowing in the primary circuit of the ignition coil at a precise moment. When this occurs, the collapsing current induces a high voltage in the secondary winding of the coil. This causes a very large voltage to appear at the coil output for a short period, enough to arc across the electrodes of the spark plugs. So very basically the Points are a precision timed on/off switch.

The points are mounted on a plate that is able to rotate relative to the Points Cam to provide for timing adjustments. The Points are activated by the Points Cam mounted to the left hand Camshaft by means of a Mechanical Advancer unit. The position of the Points is set so that they open thus stopping the current flow through the coil (and generate a spark) at the exact moment needed to ignite the fuel a few degrees before the top of the piston's compression stroke. Actual ignition timing is set a few degrees Before Top Dead Center (BTDC) to allow time for the ignition of the fuel air mix to develop so that it peaks roughly at TDC and is complete at @ 20 degrees past Top Dead Center for most efficient operation. For the GL1000 the base lines are 5 degrees BTDC 75-77 year models and 10 degrees BTDC 78/79 year models. These baseline differences are driven by the more aggressive Camshaft profile of the earlier GL1000. As the engine accelerates the Mechanical Advancer is activated by centrifugal force starting about 1450 rpm and proportionally advances timing to the full advance of @ 37 degrees BTDC at 2600 rpm. Because of the higher rpm this advancing of the ignition point is needed to allow the fuel Air mix time to fully ignite at or about TDC.

Note: there are differences between the “Early” and “Late” GL1000 advancer’s due to the difference in the timing baseline so these components are NOT interchangeable.


Ignition Coils

The ignition coil consists of two transformer windings sharing a common magnetic core; they are the primary and secondary windings. The Primary side is where the Ignition System provides a switched voltage to create the spark released from the Secondary side. In the case of the GL1000 that voltage may be anywhere between 6.4 (or lower on systems not operating at peak) and 10 plus volts. The voltage in the primary side is fed into a coil of wire wound around an Iron core that induces a voltage in a very similar setup on the secondary side. The voltage fed into the primary and the ratio between the number of windings on the Primary and Secondary determine the output voltage of the Secondary. So for example if you had a full 12 volts and a Primary winding with 30 coils and a Secondary winding of say 18,000 coils then on paper you would have an output of @7200 volts. Internal wire resistance and other physical factors will result in some parasitic loss.

If anyone cares the formula is Secondary voltage over Primary voltage equals number of turns on the Secondary over number of turns on the primary. Or VS/VP = NS/NP.

For the GL1000 application due to the Wasted Spark design the Secondary winding of the coils are tapped at each end as opposed to the standard of grounding one end as is done in most applications.

For testing purposes removing the Spark Plug caps and their associated 5,000 ohm resistor should result in a resistance reading of @14,250 ohms when reading from the # 1 High Tension lead to the # 2 HT Lead. And the same when reading from # 3 to # 4. This is testing the secondary side of the coil. To test the primary side it is necessary to gain access to the coils. Readings should be @1.8-2.2 ohms on the primary side. Some book references list them as 2.4 but I personally checked 7 different coils with a calibrated fluke and got readings of 1.8-2.2 ohms

Ballast Resistor

The Stock Ballast resistor is a 3 ohm resistor built into a ceramic heat sink. The Ceramic is just there to assist the resistor from overheating and damaging itself. Yes they get VERY Hot!! What is a Ballast resistor? Per Wikipedia: “is a device intended to limit the amount of current in an electric circuit”. OHMS Law states Current equals Voltage over Resistance. So if you have a basic 12VDC circuit you increase resistance in order to reduce the Current flow. So if there were no Ballast resistor in the system the coils would be the only resistance (@ 2.0 ohms) and that would result in a current flow of @ 6 amps. That is a lot of power considering you only have 20 coming out of the stock stator. Power generates heat and heat is not good for electrical components. Adding the Ballast resistor increases the circuits resistance to a total of 5.0 Ohms and subsequently reduces the current to @ 2.4 amps. So the advantage of the Ballast resistor is reduced heat generation of the coils, reduced wear of the Contact Breaker Points, and reduced current draw of the system. The difference of 3.6 amps saved is enough to operate one 35 watt driving light. 3.2 amps x 12VDC = 38.4 Watts save by running the resistor. The GL1000 ignition system operates on a lower voltage so these examples are not precise but give you an idea of what is accomplished here.


Capacitors also called Condensers

Years ago Capacitors were called Condensers and still are in some automotive applications. The name has changed but the job has not. A Capacitor is a voltage storage device not unlike a very short-term battery. It receives electricity and stores it until it is called for. In the ignition application it also acts as a buffer.

So in the storage role it takes voltage from the coils and stores them. When the Points open and the current flow stops the induction field around the primary coil winding starts to collapse, now the Capacitor starts to dump it’s load of electricity. This slows the collapse of the induction field and makes for a longer sustained spark. The Capacitor and the Coil Primary windings create an oscillating LC (inductive capacitance) circuit that I will not attempt to explain (because I don’t understand enough about it). But the values of the Capacitor must be matched to the circuit as it effects the length of time involved in the charging and discharging of the Capacitor and will effect the length and effectiveness of the spark.

The Capacitor also acts as a buffer. When the Induction field around the primary winding of the coil collapses it creates a small Electro-Motive-Force (EMF) Pulse of electricity that gets sent down the wires toward the points. The Capacitor acts as a buffer and absorbs a large portion of that electricity reducing the arcing and burning of the Points contacts extending their operating life. So if you remember when Grandpa’s truck was burning up Points the first thing that was changed was the Condenser and that usually fixed it. I have read of values of 250 volts of EMF that will come back through the primary when the field collapses.

The GL1000 has 2 Capacitors. They are manufactured in one bracket so many people think it is one unit, but in fact it is a 2 separate electrical devices. One side serves # 1 circuit and the other side serves # 2 circuit. There is only 1 wire feeding each Capacitor so the ground of the unit is critical (much like the early turn signals). The value of the stock Cap is .24MF, this value ties into the spark duration, the coil required charging time, and the Contact Breaker Point Dwell time.



High tension Leads, Spark Plug caps, Spark Plugs

The Stock High tension (HT) Leads are simply a very good insulated wire. There is no designed internal resistance. On the 1000 they are not removable from the coil. On the 1100 they are and can be replaced.

The Stock Plug caps are another story. Plug caps screw onto the ends of the wires. If they become loose often removing them and cutting off a ¼ inch of wire will refresh their connection with the HT Leads. Inside the end of the Cap (where the spark plug goes in) is a slotted screw. Under that slotted screw is a 5,000-ohm (5 K-ohm or 5K) Resistor. It is not uncommon for these to fail. This is where part of the Test Value of @ 24,250 ohms comes from on the stock system. 5,000-ohms for each plug cap and 14,250-ohms in the coil itself. Eliminating these resistors will result in a slightly hotter spark but will also result in more stored electrical energy in the secondary windings when the voltage has dropped below the level needed to sustain the spark. This stored voltage then is transferred (through induction) back to the Primary windings and back down the line to the Condenser and points will contribute slightly to premature wear of the Breaker Points Contacts.


The stock Spark Plug for the GL1000 application is the NGK D8EA or D7EA for cold weather with a gap setting of .024-.028 inches. This is a NON-Resistor type of plug meaning it has no internal resistance. The initial production of the GL1000 was designed as a nekid bike and there was minimal concern regarding Electrical Magnetic Interference (EMI) at that time. As the evolution progressed into the GL1100 line with radio’s and such a Resistor style plug (NGK DR8ES) was installed to reduce the engine’s EMI Signature and resulting Radio Frequency Interference or RFI. The NGK Iridium equivalent is not available in a NON-Resistor model and is DR8EIX. These are an excellent upgrade from the stock application and seem to work particularly good with the Wasted Spark Ignition system. My experience has been that the stock plugs result in a performance deterioration starting in the 7,000-7,500 mile range, exactly where the scheduled maintenance calls for replacement! So for me that is less than one season of riding and I have often developed a slight hesitation or bog that went away with fresh plugs. Never ever forget to do the simple stuff first when chasing a problem!


Ignition Switch and Start Switch



Start Switch does 3 things

a. disables the headlight (US Models without the Headlight on off switch)
b. engages the Starter solenoid
c. bypasses the ballast resistor to provide full voltage to the coils for a hotter spark for starting

[sunnbobb]

Good job!

[JBz]

Im wondering if i can use the dr8es-L plugs in place of the dr8es on a 78 gl1000 with dyna all the way. JB

[roncar]

Im wondering if i can use the dr8es-L plugs in place of the dr8es on a 78 gl1000 with dyna all the way. JB

IIRC, I was doing some research recently, and the "-L" indicates a half heat range lower (like eq to 7.5 in your example.) I think the original plugs for the 1000's were D8ES-L which were discontinued and replaced with D8EA. From my understanding and what I've told, your answer is yes you can.

[bum]

HeyChief.........I started reading this post and then I remembered why I chose ADR "A" school , my squadron ( VQ-2) was filled with guy's who would understand it! Hell even my Dad who was a first class radar tech during WWII , would try to explain electronics to me and it would go in one ear and out the other, but it looks well written.....where do you find the time?

[Whiskerfish]

I don't really understand most of either but I can fake it pretty good

Actually I was an Aviation Electronic Tech for my rating but I spent most of my career as a helicopter Crewchief and did a lot more Mech and Airframe work than Electronics. Most people had no idea I was actually a "Tweet"

[pdalyphoto]

Noob question (beware!)

When you test a spark plug against the engine case of say, a 76 GL1000, as I've seen done by a bunch of people on the Youtubes with other bikes, would you expect to see a fairly bright or strong spark. I suspect my current coils to be bad and when I tried this test the spark was very minimal. Just enough to fill the gap of the spark plug but hardly visible from more than a few inches away. Also, I checked my coils and I was getting about 14500ohms to the plug wires, but the coils were measuring around 3 +/- a few decimal changes. If these are out of spec should I believe that the spark isn't nearly what it should be? It won't run currently and I finally got it to run off of starting fluid but only for about 3 seconds. I hope this was legible.

[Whiskerfish]

I apologize for not seeing this sooner. 2 weeks to wait for an answer is pretty sad

Anyway yes the stock ignition system is weak but it does work. If you had it running on starter fluid then my immediate suspicion would be that you have spark and you need to look at fuel.

[bob]

I don't really understand most of either but I can fake it pretty good

Actually I was an Aviation Electronic Tech for my rating but I spent most of my career as a helicopter Crewchief and did a lot more Mech and Airframe work than Electronics. Most people had no idea I was actually a "Tweet"

Tweet.....AKA Conehead

Very well written explanation, BTW.