Pony motor starter 12 volt conversion question

chas036

Member
I would like to change my 720 from 6 volt positive ground to 12 volt negative ground if possible. I found a set of 12 volt car coils I can use to replace the six volt JD coils, so this will not be a problem. Also I already have a 12 volt alternator that I can use to charge with, and I have a 12 volt fuel gage I can use, and I already have 12 volt lights I can use.

My concern is the the starter. Will the 6 volt starter on a pony motor run without damage if you use 12 volts and negative ground? Will 12 volts effect the capacitors or the points in any way?
 
"<font color="#6699ff">[b:654c4848f0][i:654c4848f0]Will the 6 volt starter on a pony motor run without damage if you use 12 volts and negative ground?[/i:654c4848f0][/b:654c4848f0]</font>"

Take a look at the information below from a <a href="http://www.yesterdaystractors.com/articles/artint8.htm">contributed article on Yesterday's Tractor</a>.

"[i:654c4848f0]Starter - The existing 6-volt starter not only can be reused but most often is your only option. It is improbable that you will be able to locate a 12-volt starter that will match your drive gears and mounts. Still, real caution must be used to avoid burning out your starter. The starter will get hot under 12-volt use so you should avoid cranking for long periods and let it rest between attempts. Keep your tractor tuned up and this should not be a problem.[/i:654c4848f0]"

The previous owner of "John W", our 56 Model 70 diesel, converted to a 12 volt system.

Take a look at the photos below.

a244730.jpg" width="650"


a244731.jpg" width="650"


Note the ignition resistor (ballast resistor) installed between the ignition switch and the OEM coils.

Both our Model 40T and Model 40S tractors with 6 volt starters were converted to a 12 volt system.

Hope this helps.
 
What 12 Volt car coils are you planning to use? All 2-output car coils I am familiar with would have low resistance primaries which would make short work of your breaker points.

Unless you know of some with appropriate primary resistance, you are going to have to use a resistor in the primary circuit, which can be done with the original coils, keeping a stock appearance.

If you get a pair of two output coils for an Onan or Kohler (or equivalent) you can use them directly, with no primary resistor, and hide them under the hood. Going that route, I would use condensers for the same application.
 
In the archives at the top of your page type in :

720 pony motor distributor

I have no interest or financial investment however this person was thinking out side the box:

Bob..
a244747.jpg

a244748.jpg
 
"this person was thinking out side the box


Looks to me as is he was thinking "inside the box"!

And doubling the load on his breaker points!

<img src = "http://gardentractorpullingtips.com/images/5275548s.gif">

<img src = "https://www.kohler-engine-parts.opeengines.com/images/magictoolbox_cache/8c95d73fec130487c102a73bf1ab42ce/4/9/4995/thumb200x200/3254873476/kohler_277375.JPG">

Here's a ccouple of examples of true 12 Volt double coils that are readily available.
 
I already have that setup you see in the photo with 4 separate 6 volt ford tractor coils. It works well. I thought of just buying four 12 volt tractor coils and using the same setup if I change to a 12 volt battery positive ground.

If I went to positive ground, would I have to rewire the coils in anyway?
 
The pony motor hasn't got much compression, so if it doesn't start right off, don't continue to spin it, the 12 volts will throw the windings out of the starter.
 
I checked those coils and Kohlers were like $170, but the other brand Onan were 50 to 70, but which one do I use since there is all types to choose from?

Would I use the same 6 volt condensers that come with the pony motor points set, or use something different?
 
My 720 came with a spare pony motor. The one on the tractor was rigged up with a messy 12volt set up, and had no spark, so I put it back to stock. When I hit the starter then it was like my brand new 6volt battery was dead. I switched the starter out with the one from my spare and it started right up. I wondered if they had the original starter rewound for 12volts. Is that even possible?
 
(quoted from post at 10:57:30 12/06/16) I would like to change my 720 from 6 volt positive ground to 12 volt negative ground if possible. I found a set of 12 volt car coils I can use to replace the six volt JD coils, so this will not be a problem. Also I already have a 12 volt alternator that I can use to charge with, and I have a 12 volt fuel gage I can use, and I already have 12 volt lights I can use.

My concern is the the starter. Will the 6 volt starter on a pony motor run without damage if you use 12 volts and negative ground? Will 12 volts effect the capacitors or the points in any way?

Easier to buy a good 6V battery!
 
The coils I posted photos of both do the same thing, just a different manufacturer's "take" on how to make things. As I wrote, if using one of those coils I would use a condenser for the same application.

As to using the original condensers, 6 or 12 volt system is not an issue to them, as they are likely rated in the 300-400 Volt range.

CAPACITY, rated in mfd's is what's important. Typical ignition condensers run in the .15 mfd to .25 mfd range.

The condenser needs to match the coil, or breaker point pitting will occur.

The original condensers would definitely work to get it started, point pitting will show up later if they are too small or too large for the chosen coil.

From an old Delco Remy manual...

"Contact pitting results from an out of balance condition in the system which causes the transfer of tungsten from one point to the other so that a tip builds up on one point and a pit on the other. The direction in which the tungsten is transferred gives an indication for correcting the situation. If the tungsten transfers from the negative to the positive point increase the capacity of the condenser. If the transfer is from the positive to negative point, reduce condenser capacity".
 

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