No spark

[Soundguy]

3a should be fine.. most points are in the 3a / 4a region anyway.

The area of concern i saw, is that the poster has a voltage drop ov 3v between the output of the ignition switch, and the input of the primary on the coil. That is a cause for concern...

Wire trace needs to be done. Only thing it may be is a ressitor inline to run a 6v coil on a 12v system.

Otherwise it is a bad wire / connection.

to the poster:

Try the jumper from the battery to the coil, like I mentioned.. there should be no voltage drop before the coil, unless a resistor is used, or you have bad connections / bad switch..

Soundguy

 

[Syncro]

<font color="blue"> There is current thru distributor when points are closed and none when points open. Therefore I should be getting high voltage out of coil but am not. </font>

You probably know this, but just in case you don't, in order to get hi voltage out of a coil the points have to be operating, make and break the input current. In other words a static voltage to the coil will produce nothing, zero volts output. This is a DC circuit, so the coil will only work in short bursts corresponding to the points opening and closing. Thats why the engine must be cranking to check for coil operation.

 

[cp1969]

Or, manually open and close the points in lieu of cranking. But yes, secondary output is nothing until the points open.

 

[1savoy]

dgh,

Being a 1958, is this tractor a 6v or 12v. You may have stated it and I missed it. This tractor may have been a 6v positive ground. You may want to make sure you are connecting the coil properly. A positive ground system will have the + side of the coil going to the distributor and the - side to battery voltage. I would also check all your connections. Clean them and use dielectric grease. I would think a 2v drop to the coil is fine, for a 12v system. 3v sounds a little too high though.

Good luck,
Russ

 

[Soundguy]

</font><font color="blue" class="small">( I would think a 2v drop to the coil is fine, for a 12v system. 3v sounds a little too high though. )</font>

There shouldn't be any tangible voltage drop from the key switch to the primary post on the coil, unless there is a resistor in line.. When I saw tangible.. you may see x/10 or x/100 voltage drop, due to wire resistance, and connectors... anything 1v and above means you have bad wireing/dirty/loose connectors.. )

Soundguy

 

[Marlowe]

What I know about point type ignition systems shouldn't take but a few seconds to relate, so here goes. Most of them that operate off the battery voltage run on less than full battery voltage. This voltage drop is accomplished with an external resistor, internal (inside the coil) resistor, or a resistor wire. The resistor wire is a tricky one because it causes the most head scratching. It looks just like any other wire, but is produced to result in the needed drop of voltage.

Why do they do that?

When a starter motor is engaged it is the primary and extensive draw of amperage from the battery, leaving residual voltage of something less than twelve volts for the ignition system to spark and crank the engine. Therefore, the ignition system system is designed to give adequate spark on less than full battery voltage. There is a bypass circuit, usually coming from the starter solenoid which goes directly to the coil. This provides all the voltage the battery has available during cranking to the ignition circuit.

As soon as the engine starts, the full battery voltage is available, but is too much. If full battery voltage is supplied full time to the ignition system, the points burn out prematurely. That's where the resistor circuit comes in, reducing the voltage to what the system was designed to run on.

Back to the basics of a battery driven, point type ignition system. For it to work we need points with continuity, set at the proper gap. We need a good condenser/capacitor. And we need a good coil with the right amount of voltage fed into it. A good coil will have the proper continuity in the primary and the secondary circuits. The ohms resistance can be measured in a coil with a meter, but what the specs are supposed to be is hard to find information. In general though, the primary circuit will have very little resistance, and the secondary will have a lot more, but not an open circuit. Remember, a hot coil will test different than a cold one, and no test is definitive. As soon as we assume, or take a test result at face value, it will bite us.

I hope this will help, and good luck with it.

Tom

 

[1savoy]

Tom,

Very well put.

Russ

 

[Soundguy]

</font><font color="blue" class="small">( Most of them that operate off the battery voltage run on less than full battery voltage. )</font>

I'd hesitate to say 'most'.

Of my small 'fleet' of antique tractor, I've got a couple diesel and magneto.. the rest are battery ignition.. and Only one used an "oem" ballast resistor.. A 46 2N ford.

</font><font color="blue" class="small">( leaving residual voltage of something less than twelve volts for the ignition system )</font>

Again.. most old points system tractors were 6v.. not 12v.. you saw 12v pop up big in the mid 50's.. around when diesels were becomming popular.

</font><font color="blue" class="small">( There is a bypass circuit, usually coming from the starter solenoid which goes directly to the coil)</font>

Early units used a variable resistance ( heat coeficient) type ballast resistor to manage coil voltage/current. At startup resistor was cold.. dropped less votlage.. thus more volts to the coil for starting. Very rapidly resistor heated up, reducing volts/current to the coil. In the antiques I collect, I don't commonly see the ignition bypass solenoids.. but more of the temperature coeficient systems.

In 'general.. due to points surface contact area.. you look for 3-4 amps of current in the primary.. that yeilds a 12v ignition coil with a primary resistance of about 3 ohms.. Same reasone why a 6v coil has in the 1.2-1.8 range of primary resistance.

If you search on the web, you can find some good resources on 60's cars that list coil voltage, as well as ballast / ignition resistor values. If you do the math.. most add up close to 3 ohms for a 12v system primary.. etc...

Soundguy