The Stovebolt Site Forums The Shop Area Engine Shop Timing light inductive pickup?

My timing light cant seem to pickup anything off of 6 volt plug wires while it works fine on 12 volt. Ive been using a 12 volt power source, and very, VERY occasionally I can get a strobe from the light itself. Ive tried the 6 volt battery just because with no effect. What can I do to get the inductive part to pick up the power surge for spark more effieciently?

Im using steel cored cables with 7mm insulation. Ive tried patching in a wire from a cable thinking maybe the insulation was to thick. What am I missing? Again, 12 volt picks up and strobes perfect.

And yes mine is supposed to work on 6 volt using a 12 volt power source.

Thanks, Jeff

The inductive pickup should just work, the spark plug voltage isn't dependent on the primary voltage.

Are these plug wires shielded? You might try swapping the plug wire with another one. Try the one that worked. Why are you using steel cored wires? You actually want some resistance in the plug wire so standard cores probably work better.

Josiah,

In a electrical transformer, secondary voltage is determined by several things...number of windings, tap location and primary voltage.

Isn't a automotive coil a transformer? Wouldn't secondary voltage (spark voltage) be partially dependent on supply voltage!

Stuart

Im using steel cored wires to supply a hotter-stronger spark due to it being 6 volts! And yes it makes a BIG difference. Most of the autotmotive places dont sell steel cored plug wires cause of the interference and noise issues they cause.

Stuart I dont know what the hell your talking about! But youve got me confused as hell!

Having bought & used a few timing lights thru the yrs. I can tell you they are not all created equal. But, the first thing I'd do is pull a plug wire while running & see if that sucker won't jump a big fat blue spark. Now, if you see you have a good spark, all you need to do is look for a good light. I have a Proto I bought new around '70, non inductive, & a Cal-Van I got on ebay a couple yrs. ago, it's even older, both have a strong light. I've used some quite expensive shop ones that weren't as bright. But, I have no 6V. motors so can't tell you for sure there.
Have you checked the primary voltage to your coil while running? You could jumper off the batt. to it & give it a full 6V. while timing.
Doug

The only time I was able to get this thing to strobe properly was by pulling a boot and letting the arc cross from the wire to the plug by less then a hair on a gnats @ss.

I getting kind tired of getting the cr@p shocked out of me doing this, pulling wires and trying to make it work...

Im still looking for help?

Thanks, Jeff

Jeff,

I probably have this theory wrong, but it's my understanding that ignition wires are engineered with some resistance which allows the voltage to build slightly which results in a stronger spark. This also happens when the voltage reaches the electrode on the plug...it builds until it has sufficient strength to jump the gap.

Because you are using solid core wires, they might not have enough resistance to allow the voltage to reach a adequate level for the inductive pickup to read.

I know the inductive pickup on my timing light has a big warning label on it not to drop or slam it...it's rather delicate. Could your pickup be screwed up!

When you pull the plug wire and the light works, I think you are creating artificial resistance in the wire and the pickup and sense it and the light triggers.

I might be all wet on this theory...lets see what the guru's have to add.

Stuart

Jeff,

See if your timing light is marked for 6 and 12 volts. In the past, timing lights were all made to work on either voltage, and were marked as such. I haven't looked at newer lights, but it may be that 6v timing lights are not in the current crop of tools available from auto supplies and tool stores. To get around your problem, and avoid getting shocks, hook your timing light to a 12 volt battery while you time the 6v engine.

As for your metallic spark plug wires, they were original equipment for a long time, and using them on your vehicle is all right. They do provide a little more spark current than resistive wires, hotter spark so to speak, and don't drop secondary voltage as resistive wires do. Their primary drawback, as you noted, is radiated radio-frequency noise that causes crackling in AM radios and "snowy" bands in television sets. Those concerns were the origin of TVRS (television and radio supression) ignition wires that later became just "RS" or "supression" or "resistor" wires. The 7mm diameter is the proper size for your setup, although a larger diameter won't/shouldn't cause any trouble.

Your ignition coil is in fact a transformer (technically an autotransformer), but that point is immaterial for your timing light issue- unless you have changed the coil to something other than an original-equipment replacement. If you changed the coil, it is a remote possibility that you installed a 12 volt coil with an internal ballast resistor. That combination with your 6v ignition system will cause you trouble in the form of a weak spark, and cause your timing light to work as you describe.

Harvester

The timing light is a 6/12 volt combo. The manual says use a 12 volt power source and add a ground from the 12 volt vehicle to the 6 volt vehicle.

Thanks for the input, it is a 6 volt coil.

Stuart the light works fine on my 12 volt trucks, no problem there. Ill try a non steel cored wire and see if that effects anything.

I really appreciate all the input rather then the whole 'guess the timing' routine. Thanks, Jeff

jeff i bought a light yesterday at autozone it said to use a 12v bat and a ground jumper as you stated mine works fine and i have 6v and solid core wires. does the truck run good if not i have an
idea. if the plug is not firing the plug itself then there isnt any power used and nothing for the pickup to read but when you pull the boot the spark arcs to the plug thus using power and the pickup
reads it.

Regardless of whether or not the truck is running it should strobe so long as power is to the coil. But yes it is running now.

Im up for any ideas here so keep em coming!

Thanks, Jeff

I have more than 10 years experience as an electronics technician, and I see a few flaws in theory in your post.

1. Everything presents a resistance to electrical current. Even 'super-conductors'. The quantity of the resistance is what makes the difference. In a series circuit, like an ignition system, resistance will always cause a decrease in both voltage and current, but the characteristics of the spark plug wires, unless you are using coat hangers as substitutes, is usually not a factor.

2. Actually, while the points are closed (electrical short) battery current charges up the ignition 'condensor'. When the points open, the condensor discharges through the coil because there is no other path for current. The coil is a transformer, as mentioned before, and converts the 6 or 12 volts, at relatively high current, from the condensor, into 10,000 to 100,000 volts at very low current, and sends it to the center connector of the distributor cap, where it is distributed in accordance with the position of the rotor. (The low current is what keeps us all alive. Voltage does not kill. Current does. More than 1/2 amp of current can kill you. the CURRENT through the spark plug/wires/gap is only a few milli-amps. The high voltage is required to jump the air gap between the spark plug electrodes. This air gap represents a large resistance.

There is absolutely no reason for a stovebolter to know this much theory. It won't help your engine run better. Your engine must have the timing set correctly in order to run correctly. This does not require that your engine even be running, as long as you can find the correct timing mark.

All you need for fairly accurate timing is an ohm meter. If the vehicle has a battery in it, all you need is a six volt bulb with leads soldered to the threaded part, and the lead tip at the base. Set your timing mark to whatever you want. Look at the valve gear to determine when No. 1 cylinder is at top dead center. Hook your meter or test light across the points. Then twist the distributor (which I know you remembered to loosen the clamp on) until the light, or meter shows a distinct change in voltage. The light will go on, or off, and the meter will respond as expected.

Keep twisting until the transition is a fine as a frog hair, or you get tired. Either way, the timing will be good enough for the engine to run. If your carburetor and vacuum advance are any good, it will run nicely. You may do better with a timing light, but I never have except with engines that produce more than 500 horsepower.

If your coil is any good, you won't gain anything by using solid core wires. I found a 6 Volt Mallory coil on E-Bay a while back, and that is what I use to start 6 volt systems. A 12 volt coil will work, because it doesn't care. It's just a transformer. Put in 6 volts and it puts out 12,000 volts. Put in 12 volts and it puts out 24,000 volts. If your spark plug gap is anywhere near correct, you WILL get a spark.

starkweatherr,

Sheesh...do I get an A for effort!

If it weren't for flaws I would have no life at all.


Stuart

i was thinking maybe a skip in the number 1 cylinder but while im at it no the timing light will not strobe without the engine running the timing light flashes when number one fires that is what makes the timing mark visible. i now wonder if you understand the timing light

Yes a timing light will strobe without the engine running so long as power is being supplied to the coil then it is transfered to the sparkplug and causes it to arc.

Or at least my timing light will, and has on 12 volts. Its a pretty simple process and even as blockheaded as I am even I shouldnt be able to screw it up.

Jeff,I had the same problem with my truck a year ago.My truck is 12 volt,scratched my head a while.Decided to change number one spark plug.Guess what,the spark plug was bad.You might give that a try.

I appreciate the advice but I swapped it out through different plug wires trying to get something-anything at all!

I'll stand by my assertion that primary voltage doesn't affect the spark plug voltage. It does affect the duration of the spark, since a coil of the same winding can't store as much energy with half the input voltage.

Ignition coils do not operate the same way as power transformers, since the input is not sinusoidal. Inductors (coils) are current-law devices, that is the voltage induced is proportional to the instantaneous change in current. V=di/dt * L. The primary takes current through the coil and the magnetic field saturates once the points have been closed long enough. At that point no more energy can be stored in the coil and the rest of the energy ends up as heat. When the points open, the magnetic field collapses because the current went away. Since the points are open, all the energy has to flow out through the secondary side (ignoring what is stored in the condenser, that is just there to keep the points from burning out). However, there is a gap in the secondary circuit, which is the spark plug. All that energy wants to get out so the voltage builds until the spark plug arcs across, and then it all dissipates and the cycle starts again when the points close.

Coils are rated for voltage in what is the maximum they will throw, but in reality the system runs at whatever the spark plug makes it.

Resistor plugs and wires surpress interference, but they also serve another two important functions. They raise the voltage across the plug, and they also slow down the release of energy from the coil and make a longer duration spark. Once there is enough current flowing across the spark gap to ionize the air, the resistance of the gap drops rapidly. The resistance of the wire or plug electrode only allows enough current to flow to keep the spark lit and it uses the energy stored in the coil in a more efficient manner.

Most standard ignition coil systems work best with ~5000 ohms resistance between the coil and the plug electrode.

FWIW... I made a patch cable from an old set of wires for use on ignitions with a solid core. I simply plug it between #1 plug and the wire to get the light to strobe. The idea came when I remembered my Father has a timing light from the early 60's that includes a piece of wire similar to this, however the pickup is clamped onto a metal ferrul in the middle of the cable.

Scott

No big deal. 4onthefloor gave me my comeuppance later on. Somehow I forgot that the current normally flows through the coil. It doesn't just get dumped on it when the rotor mates up with one of the plug wire terminals.

Once again, this is information that isn't going to do many stovebolters any good.

Glad someone mentioned a faulty spark plug. I never would have thought of that.

Josiah,

In an effort to beat this old horse to death, let me try to get straight on this coil idea. What is the purpose of the bypass switch or ballast resistor in the ignition circuit on many of these trucks?

Isn't this an attempt to give the ignition system the benefit of full system voltage when the starter is demanding most of it during a 'start'. Doesn't this say that the more voltage you put into the coil, the more spark energy you are going to get out of it.

I am not an electrical engineer, but I thought this is how it worked.

Stuart

Hi Stuart,
I don't see a resistor in the wiring diagrams and have never seen one on a 6 volt system.
If you look at the way a resistor is wired into the system you will see that it is in series with
the ignition terminal on the switch and the primary winding of the coil.
This can only drop the amount of voltage going to the coil.
When doing a 12 volt conversion a resistor is used to drop the voltage to 6 volts for the original 6 volt coil.
If you replace the coil with a 12 volt coil you would still use a resistor to drop some of the voltage because
a 12 volt coil is actually designed to run on approximately 8 volts.

Stuart,

Your are correct with your understanding of the ballast resistor and the starting bypass. The ballast resistor drops approximately half the system voltage when coil primary current reaches the saturation level- about 4 amps for a typical contact-point ignition system. That means, with the key on, engine off, points closed, and 12 volts at the battery, the ballast resistor drops about 6 volts. The bypass circuit helps the ignition system when the starting load pulls the ignition system primary voltage down to 9-10 volts. With the ballast resistor in the circuit, the coil would get roughly half that voltage and the coil secondary output would be reduced, possibly to the point where spark plugs will misfire because of insufficient secondary voltage available, or the spark current will be insufficient to ignite the fuel mixture in the cylinder. The bypass circuit applies the full system voltage (cranking voltage) to the coil primary, which causes more primary current in the coil, which in turn, results in a hotter spark (higher spark current) for starting. Some coils have the ballast resistor built into the coil, and no starting bypass circuit. Vehicles that used those coils sometimes had starting difficulty in cold weather when oil viscosity and reduced battery capacity both caused a higher starting load and lower primary voltage.

The reasons for the hard starting when cold are first the fuel mixture in each cylinder is somewhat lean, not rich as is commonly assumed, and the cylinder compression is higher than at just about any other time- more on that if anyone is interested. Spark plug firing voltage is raised by both lean fuel mixture and high compression pressure. Contributing to high compression pressure is ambient air temperature, so in cold weather, air is more dense, so compression pressure is raised.

Six-volt electrical systems don't use a ballast resistor in the ignition system.

On the original question of the timing light, the advice on the fouled spark plug is correct. A quick check on the wires and spark plugs is to connect the timing light to another cylinder. If it works reliably, the irregular flash is the result of a wire or spark plug matter. On most six-cylinder engines you can time the engine on number six cylinder- half way through the firing order (one crankshaft revolution), so the timing marks are in the same place as they will be for cylinder number one. All you need to know for that process is the firing order for the engine and the specified timing cylinder, number 1, usually, then the first cylinder in the second half of the firing order puts the timing marks at the same place they will be for the 'original' timing cylinder.

Harvester

Thats kinda what I was trying for but now that you mention it I think Ill engineer something a bit more sufficicent for the task!

Thanks! Jeff

And what the heck does FWIW mean??? :confused:

I also thought the same, as in the coil outputs such a high voltage even hooked up to a 6 volt battery it should still function. It just doesnt make sense that a 6/12 volt battery would make a difference other then how bright your strobe light might be.

Jeff,

This poor old thread has taken some strange turns. Isn't your timing light connected to your battery? The inductive pickup clamped around the plug wire is only a trigger! The strobe is being powered by the battery.

Stuart

FWIW = for what it's worth, which around here frequently is 'not much'

I've been thinkin the steel core wires are your problem, less surface effect on steel than copper or carbon?

Bill

No, steel-core wires, or any metal-core wires, are not the problem with this timing light, unless the wire used for the trigger is broken ahead of the trigger connection. A carbon track or crack in the distributor cap might shunt the spark voltage away from that particular wire, causing the light flash to be irregular, but that condition would most likely cause an identifiable misfire. Given that the light flashes somewhat regularly when the associated spark plug wire is disconnected and the spark allowed to jump a small distance, the carbon track/crack possibility seems unlikely. With that, I'm leaning toward the pick-up probe being at fault, or the power supply in the light is at fault. The power supply in the light has to generate something around 300 volts DC in order to trigger the flash tube in the light. The power supply may work adequately with 12 volts in, but not with six volts. The pick-up probe probably is replacable, depending on who made the light. I believe someone mentioned that the probe is a clamp-on type. Clamp-on probes often use a ferrite core which may break if the clamp is dropped, then the operation is erratic. An electronics technician familiar with strobe lights could check the power supply to see if it is working, and maybe repair it, but it might be cheaper to buy a new light. After you have eliminated all the other possibilities. One place to look for a repair shop would be a shop that repairs camera flash equipment. An automotive timing light is nothing more than a camera flash unit with a focusing lens rather than a diffusing lens. And a power supply to work on either 6 or 12 volts input.

Harvester

Oh I found the problem I was pointing the timing light the wrong way! They should really label these ends for which way to point them... I wonder how you see the strobe with that blinking light on the back shining in your eyes...

Problem solved. Swapped the cap and rotor out and we have perfect ignition using a 12 volt source. The odd part is that it was still sparking before so maybe the spark wasnt strong enough to register before the new cap and rotor???

Thanks for all the weird twists and turns this has taken though, my next guess was government involvement... Sshhh... Theyre watching...

I have to suspect a carbon track inside the distributor cap. As I understand it, when the spark plugs are worn, or provide an unusually high resistance, the spark may arc along the inside surface of the cap. If it does this for a while, it lays down a carbon track. This might give you a situation where you have an intermittent miss that can be made better if you replace the spark plug and wire, but the carbon track is still there. The thing is that the carbon track probably won't lead to the cylinder it is supposed to. This will give you a weak spark in another cylinder, which will not have any noticeable effect since only one cylinder is ready to fire.

If the carbon track bypasses the number one cylinder spark plug wire connector, that might give you intermittent, or no spark to the No. 1 plug wire, which is the trigger for the timing light. It might just be that the spark isn't strong enough to trigger the light.

Sometimes you can clean the cap out, but why bother?

Someone once told me that all coils are 6 volt. I don't think that is true, but I do believe that most coils aren't comfortable with a steady diet of 13.8 volts, which is what healthy 12 volt alternators and generators produce.

After all these years I finally read about an extra starting circuit that increases the voltage to the coil during cranking. As mentioned above the cranking voltage will drop to 8-9 or 4-5 volts, depending on whether it is a 6 volt or 12 volt system.

Am I correct in thinking that this circuit only exists on 12 volt systems and bypasses the ballast resistor?

yes you are correct, became standard when the resistors started along with 12V .... but then the ballast res was replaced with internally resisted coils, so what does that say about the usefulness of added juice to coil at starting??

Bill

Where is the bypass circuit located, and what does it consist of?
If it bypasses the ballast resistor wouldn't a second wire be needed to go to the + side of the coil?
We should probably move this topic over to the electrical bay.

doesn't have a 2nd wire to the coil, but does have 2 wires on the 'coil end' of the resistor, on some versions its actually on the resistor, some on the ign sw

on the V8 trucks, there's a secondary circuit in the ign sw - when the start position of the sw is engaged, it puts contact to the "outlet" side of the ign resistor, when the on position is engaged, the power goes to the 'inlet' of the resistor - on the foot start version, the foot sw puts power to a contact that goes to the resistor via the switch connections

Bill

Ballast resistors are one of three different types, but all are nichrome wire, which is a resistive wire. A porcelain block with two terminals was the most common type on early GM vehicles. The bybass wire connects to the coil side of the resistor, so two wires there. The porcelain block has the nichrome resistor wound in a coil inside the block. I think Ford used a similar type, but it had a metal case, if I remember correctly. Later GM and Ford vehicles used a stranded resistor wire laid in the front-end wire harness. This wire connects directly to the coil primary + terminal; the bypass wire attaches to the same terminal on the coil. This setup was often called the 'loom resistor' or 'harness resistor' or 'internal resistor.' The other type is commonly called 'external.' The 'internal' resistor wire has a high-temperature insulation with a white fiberglass jacket. The wire looks like steel, but the material is nichrome, which is much stiffer than stranded copper of the same size. Another resistor is the two-element unit used by quite a few Chrysler vehicles. I don't remember the purpose of the second side in the Chrysler units, but I think it has to do with the alternator or voltage regulator they used. Bypass circits connect to the coil by way of a connection in the ignition switch, or off a terminal on the starter solenoid. Delco starter solenoids have a terminal marked I, Ign, or R for the bypass- I don't remember all the variables. Ford systems and others that use a Ford starter circuit have a connection on the fender-mounted solenoid/contactor for the ignition resistor bypass. I think those are marked I or Ign for the ignition terminal- you can hot-wire a Ford system quite easlily with that setup. Some Chrysler systems didn't use a bypass system because the ballast resistor was built into the coil primary. Those often caused hard starting in cold weather. Chrysler also used a bypass circuit in the ignition switch, or on a starter relay. Memory is foggy on some of the Chrysler systems.

Harvester

I just bought a new Mac inductive timing light last week and in the manual it states that "solid copper ignition wires can interfere with the proper operation of the timing light." They recommend to temporarily replace the solid copper number one ignition wire with a resistive type wire for the test and then reinstall the original wire when done.

Hmmmmmm, imagine that!

Stuart