Need help - Cub with no spark

C

ceejaycee

New member
Hi, I am visiting my Dad and attempting to help him convert his Farmall Cub WITH MAGNETO from 6V pos ground to 12v neg ground. We have completed the conversion, but we are getting no spark. The tractor has not been run in awhile, so I am not sure if the tractor had spark before we started the conversion or not. 6V Battery was completely dead when we started, I am only visiting for 2 more days so running out of time to get it done. please help ASAP.

Here is what we have done:
For the 12v neg ground conversion:
1. Removed generator and VR
2. Installed 1-wire alternator
3. Switched the wires on the ammeter ( for neg ground conversion )
4. Ran wire from positive side of ammeter to main terminal on alternator
5. Put in 12v battery hooked up neg ground

Did not get spark, so we decided to install the external 12v coil option:
1. Ran wire from positive side of ammeter to positive side on external 12v coil
2. Removed condenser from magneto
3. connected negative side of coil to external wire post on magneto - (this is what ignition kill switch normally connected to) - assume this connects directly to the points
4. Connected plug wire from external coil to center post of distributior

No spark! Can someone please review the above and let me know if we have done anything wrong?
We are checking for spark with both a test light connected directly to a plug wire output from distributor (and ground) and also checking the coil output directly with test light. We also checked for spark on a spark plug directly attached to a plug wire grounded to engine (just in case test light was bad).

Other observation: The coil gets VERY WARM when it is connected as listed above.

What are we doing wrong? Please help fast- don't have much time before I have to leave!! Thanks!
 
First thing, why did you remove the condenser? It needs to be present, that's probably why the coil is getting hot. Clean and set the points, should be .013" gap. Make sure the insulator, where the wire stud passes through the mag housing is in good condition and not allowing a short to ground. Also, make sure the connections inside the mag are not shorted to ground. These checks should get you started.
 
I would say the points need filing from where it has been sitting. If you can hook the magneto back to the way it was originally and file the points you hopefully will be good to go!
 
Thanks for the replies. We removed the condenser because I though that was required when you use an external coil. Our goal on this project is to convert over to a Neg-Ground system using an alternator and external coil. So, how does the wiring go with an external coil?
We currently have: 12v power ---> POS side of external coil ---> NEG side of coil ----> external post on Magneto (with condenser removed) (this is normally the post the kill switch is hooked to). I was believing this would supply the output of the external coil directly to the points. We have the main post on the coil connected to center post on distributor. So, if we are not supposed to remove condenser - where does the external coil get wired in?
 
Did you unhook the coil inside the magneto? You have to have it unhooked, the wire from the external coil goes to where the wire of the inside coil was, the points, you will have to use the post you speak of but make sure it isn't broken and grounded out. File and check the points after that. I still don't know why you removed the condenser.
 
ceejaycee":273urvew said:
...We removed the condenser because I though that was required when you use an external coil...
Click to expand...

Think you were confusing the condenser for the internal coil. The external coil replaces the internal one. Condenser must remain in place.
 
OK, I think I am on right track now. I was able to find a close up picture of coil and points and I see there are separate wires that both to connect to the points from the magneto coil AND the condenser. So, I need to leave the condeser wire attached to the points, and disconnect the coil wire. Still connecting the (-) output from the external coil to the points. I'll try this out and see how it works. Thanks!
 
OK, new observations. Took out the points and cleaned and sanded them. Was able to get spark at points and then con firm spark out of coil. Put distributor back on and checked spark at plug- NOTHING. THEN, went back and checked spark at previous spots and it stopped sparking there too!

Now here the odd thing, with the points open, I can bridge the gap of the points ground at the hot side- and it will spark when screwdriver touches positive side. THis is basically simulating what the points do. However, the points will NEVER spark when I manually open and close them or turn the engine. THis means to be that somehow the tips of the points are not conducting. We have already files the points down until they are shiny metallic. Have no idea why a screwdriver will conduct across the points, but the points themselves won't,

Any thoughts?
 
I am going to go pick up new points and condenser in an hour - easy and cheap to replace so might as well rule those out.
 
I assume you have disconnected the original magneto kill switch and the coil is a true 12 volt coil or you are using the correct ballast resistor. The screwdriver test on the points is one I do all the time. Your points may be still dirty, unlikely since you stated they are shiny metallic, or the points are not closing all the way. When you file the points they should be regapped. They are likely not closing all the way. You filed away some of the thickness of the points and they should have been regapped . New points with the correct gap will fix that problem.

The condenser, missing or not, will not cause the coil to get hot. The condenser does make the spark so it is needed but nothing to do with a hot coil.

Coils can get warm if the points are closed for a long time such as ignition on but engine not running. The coil for the magneto should be disconnected , don't need two coils. Make sure you have a true 12 volt coil.

Once you get the new points set the gap to the battery ignition setting which I believe is 0.020. Setting at the magneto setting will give too long of a dwell time, saturate the coil, and may give a hot coil.
 
Just put the new points and condenser on and still nothing - although the screwdriver gap test still works. I have been setting the gap at magneto setting of .013...I will try .020 and report back. Thanks for your continued support.
 
Are jumping across the open points with the screwdriver? If so, then the points are not closing. If you are grounding the movable point to the base of the magneto with the screwdriver then the points are not grounding correctly.

A gap of 0.013 should still spark.
 
Good news. I was making a bad assumption expecting to see a spark between the points when it opened and closed. I checked the output of the coil and was able to confirm good spark with a test light, and then further confirmed it with a spark plug. Not sure what fixed it, because none of those tests worked earlier. I'll assume that it was the new condenser and points :D . The tractor is now turning over MUCH faster with the 12v conversion and it is firing! Unfortunately, probably got the timing alittle off - because that is what it sounds like. That's alright - definitely progress!!
Thanks to all for your help!
 
Landreo":2uytuk47 said:
Once you get the new points set the gap to the battery ignition setting which I believe is 0.020. Setting at the magneto setting will give too long of a dwell time, saturate the coil, and may give a hot coil.
Click to expand...
Stick with the original gap. Otherwise you are altering the lag angle.
 
The lag is set by the impulse. The magneto will be timed as a separate action. There is magnet timing for a magneto which is affected by the points gap but he is using an external coil. Typically the points gap will be opened when using an external coil because of the dwell time.

It should run with a 0.013 gap and will likely do fine but less coil heat and potential coil saturation with the correct dwell. Ignition coils are typically run close to saturation even with their normal dwell time.
 
I should have been more precise in my statement. With a magneto properly timed, the impulse will release creating a spark at TDC. When the speed it high enough for the impulse to no longer engage, the entire coupling and magneto rotor will rotate as a unit, with the rotor leading the coupling by 13 degrees. That is the built-in lag angle. Any point adjustment will have no effect on the built-in 13 degrees.

However if you increase the point gap, the rubbing block of the points will hit the cam at a lower position. That lower position on the cam will reach the rubbing block at an earlier point in the rotation. Thus the spark will be advanced more than it would be if set at the intended gap.

I took the shortcut of referring to this increase in the timing change from impulse engagement to impulse drop out as an increase in lag angle. Sorry for creating confusion.
 
On a magneto, the points gap setting will affect several things. Increasing the gap will advance the timing slightly but the engine will still be in a reasonable range for cub timing.

The rotor timing or magnet timing will change. The points have to open when the rotor is in the correct position related to the laminated core. Typically a slight amount past the edge of the core. The magnetic flux density is greatest with that small gap. This setting is critical to a magneto's performance and is why many magnetos are very sensitive to the points gap setting. You can't twist the magnet on the shaft so that setting, the points gap, is very important.

Increasing the points gap will decease the dwell time. A magneto takes longer to charge than a battery ignition and will need that longer dwell time so will do better with the small points setting and its longer dwell. It is unlikely a magneto magnet would be able to saturate the laminated core even with a longer dwell.

In a battery ignition, there is no rotor so there is no rotor or magnet timing to worry about.

The coil and the coil's core will charge quickly since the coil is getting a relatively high voltage, compared to a magneto, as soon as the points close. No need for a long dwell time. However, an ignition coil will run close to magnetic saturation since you will get more energy out of the physical size of the coil. It will distort the output waveform so that would not be done with a standard audio or power transformer but there is no need to preserve any specific waveform or shape in an ignition coil. If the dwell time is too long due to a small points gap then the coil may saturate. At that time,the current through the points will increase, the temperature of the coil will increase, and the output of the coil will decrease. Running close to saturation will give good results, running into saturation will decrease the life of the points,decrease the life of the coil, and decrease the coil output.

I have a tracked loader with a 6 volt coil on a 12 volt system, no resistor, been like that for many years with no problems due to my laziness related to doing it correctly. I also purchased a Bolens 800 garden tractor with "ignition coil problems". The previous owner was right. The owner had placed a 6 volt coil in a 12 volt system and the top of the coil popped and was leaking some sort of oil. Sometime you can get away with a less than optimal set up and sometime you don't. Same idea with the magneto to battery ignition conversions.

There are likely many magneto to battery ignition conversions that kept the same 0.013 gap and have not NOTICED any problems but since you are in the area of the points anyway when doing the conversions why not set the gap correctly?

I cannot think of any functional advantage to leaving the gap at 0.013 but I can think of functional disadvantages to leaving that gap.
I cannot think of any functional disadvantages to increasing the gap to 0.020 but I can think of functional advantages to the larger gap.

People can do what they want, it is their equipment, but the points gap, dwell, and condenser value should match the coil you have not the coil you had.
 
Dwell is also dependent on the cam profile. I have never bothered to compare them between a Cub magneto and battery ignition unit. Since one is a 2 lobe cam and the other 4, there could be a difference which would render the whole discussion of point gap vs. dwell mute.

Dwell time (as opposed to dwell angle) and effect on coil saturation is also dependent on engine speed. With only 4 cylinders turning less than 2,000 rpm, the coil is probably always way beyond saturation.

As previously stated, retaining the 0.013 gap maintains the original timing change when the impulse coupling drops out. I'm of the opinion that the manufacturer went to some effort to decide the appropriate timing advance and designed the magneto accordingly. I try to stick with what they determined. I don't know how much the timing advance increases by increasing the gap, never measured it. It is the only factor in this whole discussion that is easily measured with common shop tools. If somebody wants to do so, I'd like to hear what they find.
 
Jim Becker":1ubo911v said:
With only 4 cylinders turning less than 2,000 rpm, the coil is probably always way beyond saturation.

I'm of the opinion that the manufacturer went to some effort to decide the appropriate timing advance and designed the magneto accordingly.
Click to expand...

Coil saturation is an end state, there is no such thing as beyond saturation, you cannot go beyond the end. No engineer would design a circuit to be saturated. There no advantages to that state and is full of disadvantages. An ignition coil is not normally run to saturation.

I modified a power transformer for something I was doing and I thought it may saturate so I used a variac to bring the power up slowly. The 120 transformer saturated at around 50 volts with the resultant burning of the insulation off my jumper wires. When an ignition coil or any coil saturates, the inductance drops and will go to zero, at that point EMF will drop, that will put an end to the output of the secondary coil so no spark, the EMF in the primary will also drop resulting in less impedance and the primary current will increase burning the points and burning the coil. Some power supplies, the common switch mode power supplies, may run near the end of their linear zone but are protected by some sort of limp mode, typically changing the pulse width, if the current to the coil would get too high.

Old school automotive engineers knew about the effects of dwell time and any potential coil saturation. They also limited the current by using the infamous ballast resistor. Just to lower the voltage they could have used a standard resistor but they use a ballast resistor instead because of its current regulation function.

I also think the IH engineers knew what they were doing, recommending a 0.013 gap for their magnetos, however the OP in this thread does not have a magneto system anymore since it has been converted to a battery ignition with a battery supplying the voltage and current to a battery ignition coil. I still say there are reasons to change the gap to 0.020 since you now have a battery supplying the power and the coil to go with that battery. No disadvantage to switching the gap but potential disadvantages to not changing the gap.

On the surface, magnetos and battery ignitions seem simple but there are actually a lot of interesting physics involved. At least to me. Good thread and discussion of the theory does apply to helping with the OP's original posting.
 
Again, I have fallen into the trap using a few words to convey an idea when I should have used many words to be precise. Yes saturated is saturated, When I said "way beyond saturated" I meant:

At 2,000 rpms, the coil cycles 4,000 times in one minute. This can be otherwise stated as one cycle every 1/4,000 of a minute. This is 60/4,000 of a second, otherwise stated as 0.015 seconds or 15 milliseconds. If the dwell angle is 45 degrees, the points are closed for one half of this time period, or closed for 7.5 ms. The time required for a coil to reach saturation will vary depending on several design factors, but 4 ms is a typical time for the older conventional systems. Consequently, the coil will be saturated and the current flow at the maximum for about 3.5 ms. This 3.5 ms is additional time that current is applied after saturation. It does nothing to increase the coil output when the points open. Whether 3.5 ms in addition to the 4 ms required to reach saturation is way beyond or not is a subjective question.

Delco Training Manual DR 5133 D "The Ignition System" (4/68) States "At low engine speeds, the distributor contacts remain closed long enough for the coil primary current to reach its maximum value . . . At higher engine speeds, the current never reaches its maximum value . . ." They did not quantify "higher engine speeds" but a graph indicates the crossover a litle over 30 mph.

Simpler to just say "way beyond saturated" but obviously open to misunderstanding.

I guess now I should explain what I meant by "crossover". In a graph of energy input to the coil as a function of speed, it is the point where the first derivative of the function is zero.
 
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