Sun Jun 27, 2010 8:32 pm
I've been restoring a 1947 Farmall Cub in my spare time over the past 2 or 3 years. It was running fine before I started the restoration, but it didn't have enough paint on it to fill a thimble. I'm happy to say that this weekend I'm far enough along that I had the privilege of starting it up once again for the first time since I began the project. I hope to have it finished in time for the Adams TN show in July.
While I was putting a new wiring harness on it I discovered that there's a mixed bag of 6 and 12 volt components on the tractor. The battery is a 12 volt, and apparently the coil is as well, because it starts and runs good. It has a distributor instead of a magneto. The generator is a 6-volt according to the model number, and I'm sure the starter is too, based on how fast it spins when I start it. The ammeter shows a small amount of charge when I rev the engine up to about 1/2 or more throttle, and if I turn the light switch to the high charge position, the ammeter jumps up another notch. It seems to be charging, but I'm sure a 6 volt generator can't support a 12 volt battery. I'm guessing the light switch itself is also the 6-volt variety. It looks old enough to be original equipment. I don't know if the lights are 6 or 12-volt. I've never seen them burn yet, but the bulbs look fairly new. The tractor is still wired for positive ground. I understand from what I've read that the true 12-volt Cubs were negative ground.
What is the process for converting a Cub over from 6 to 12 volts completely?
Given my situation, what's the best thing to do?
Should I look for a 12 volt generator? Is there such a thing for the cub, or is it an alternator at that point?
If I get a generator, what else will I need to change?
Would it be better to stick with what I have now, and just charge the battery every once in a while?
Sun Jun 27, 2010 8:52 pm
Jamie - frankly there's not much point in converting to 12 volts if you are wanting to keep a generator. One of the main reasons for converting to 12 volts is the reliability and economics of using an alternator.
The conversion can be accomplished by installing a 12 volt coil (which you may already have) and switching the headlight and taillight bulbs to 12 volt. You can keep the 6 volt starter.
Install an alternator and you are ready to go. If you use a generator you will need a 12 volt generator and voltage regulator which are the weak link in either a 6 or 12 volt system.
You are correct that most 12 volt systems are negative ground and if you switch yours to negative ground you will need to reverse the leads on the ammeter.
Sun Jun 27, 2010 8:59 pm
Jamie, welcome to the forum. You're in good hands with the folks here. There isn't a question they can't answer, at least Cub related ones.
As for the distributor, you will be fine with that no matter if you go with 6v or 12v.
Last edited by Barnyard on Sun Jun 27, 2010 9:45 pm, edited 1 time in total.
Sun Jun 27, 2010 9:06 pm
Why don't you check to see if you have a 12 volt generator. Ground the field on the generator and take a voltage reading on your armature output terminal to see whether you are at or over 12 volts.
Sun Jun 27, 2010 9:08 pm
BD has pretty well answered your questions so there isn't much to add aside from preferences I guess. One other choice is to return the Cub to 6 volt positive ground status. You already have all of the necessary ingredients - (unless there is an external ballast resistor or the coil has an internal resistor - the coil may actually be 6 volt) and there will not be the worry about the genny being able to sustain the battery. Many PO's have simply installed a 12 volt battery in a Battery Ignition system without any other changes. Yours may indeed be this way as well. If you are not going to go to an alternator, then reverting to 6 volt may be just as easy to do.
If you indeed have a 12 volt coil, 6 volt coils are rather inexpensive at NAPA and easily substituted. If you are not going to convert to the alternator, IMHO, I would set it back up as a 6 volt positive ground system.
Sun Jun 27, 2010 9:46 pm
Welcome to the Forum! You do know it's manditory to post some progress pictures... well not manditory but encouraged..
It looks like you are in good hands and well on your way to the show in July!
Sun Jun 27, 2010 10:49 pm
Thanks for the quick feedback guys.
The model number on my generator matches one of those referenced in the I&T shop manual, and the manual says it's a 6-volt generator. I'll put the voltmeter on it and make sure nothing's been changed there.
If I did revert back to a 6 volt battery, would I have to change the points or anything about the distributor?
If the coil happens to be a 6 volt coil, will having a 12 volt battery in the system damage it in any way?
Thanks again, guys.
Mon Jun 28, 2010 4:36 am
Hi Jamie, welcome to the forum.
The distributor internals are the same, regardless of voltage or polarity. If the coil is a 6v. you will need a ballast resistor in series to the coil. Yes, 12 volts on a 6 volt coil will eventually fry the coil and/or the points.
Mon Jun 28, 2010 6:32 am
Cub electrical systems, if so equipped, were originally 6 volt until the change to 12 volts during the 1964 model year. Alternators were first original on Cubs in late 1976. Delco 6 volt generators have black background on the ID tag, 12 volt models are red.
Mon Jun 28, 2010 6:47 am
jpate831 wrote:1947 Farmall Cub. The battery is a 12 volt. The generator is a 6-volt according to the model number. The ammeter shows a small amount of charge when I rev the engine up to about 1/2 or more throttle, and if I turn the light switch to the high charge position, the ammeter jumps up another notch.
Your charging system is working as it is supposed to. If the tractor were mine - I would leave things as they currently are until the charging system failed.
Engine running, amp meter showing charge. Volt meter across battery terminals will show generator voltage output.
Mon Jun 28, 2010 8:01 am
Bus Driver wrote:Cub electrical systems, if so equipped, were originally 6 volt until the change to 12 volts during the 1964 model year. Alternators were first original on Cubs in late 1976. Delco 6 volt generators have black background on the ID tag, 12 volt models are red.
Alternators were mid 1975 I believe
Mon Jun 28, 2010 9:22 am
Thanks for the quick feedback guys.
The model number on my generator matches one of those referenced in the I&T shop manual, and the manual says it's a 6-volt generator. I'll put the voltmeter on it and make sure nothing's been changed there. So, you have everything needed to put the 6 volt batter back in. Plus.. if you get a Group 1 6 volt, it should fit right in your battery box
If I did revert back to a 6 volt battery, would I have to change the points or anything about the distributor? Nope
If the coil happens to be a 6 volt coil, will having a 12 volt battery in the system damage it in any way? Yup.. in time it will fry the coil
Thanks again, guys.
Also, as Gary said, if you have the 6 volt coil you will need to add an external ballast resistor to prevent frying the coil. Right now it is probably simpler and cheaper to just pop in the 6 volt battery. Let us know what you decide to do. And don't forget
Mon Jun 28, 2010 9:48 am
Welcome to the forum. I noticed your zip code and it brought back old memories. My family had a tobacco farm there for several years, and that is where I grew up. Good luck with your '47 Cub.
Mon Jun 28, 2010 10:31 am
We may be neighbors. I am zip code 37087. If so, we need to meet.
Mon Jun 28, 2010 5:18 pm
Jamie, if asked, I'd vote for going back to 6v. Most of the reasons I've seen for converting to 12v are that either the starter or the generator failed, and conversion was less expensive. Are there any numbers on the coil that you might be able to cross-reference to see if it's 6v or 12v?
As for NAPA having inexpensive coils, that isnt' the case where I live (they're $45 for the Echlin, $25 for the "cheap" one). However, Autozone does have them for about $17. They may not know that a 6v coil exists, but tell them the part number is C809. My local Autozone even had it in stock.
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