Allis b 6 to 12 volt conversion

I just bought a 39 b and would like to convert it to 12 volt ,I have never had a tractor that still has a mag on it ,I know I'll need a GMC alternator but do I replace the mag with a gm distributor ?

I understand that the B's didn't have electric start until mid 1940 starting with serial number 43220. I could be mistaken and someone with more knowledge will correct me. Good luck with your B. 

I could be wrong about the year of this tractor because it does have a starter

Kevin,  Thank you for getting one of my favorite Allis Chalmers Tractors the B.  Check and see if you have an opening in the torque tube for a starter, a flywheel with provisions for a starter ring gear, a block with the wherewithal to mount a generator, and torque tube with the mountings to accommodate a battery box.   

Edited by Bill Long - 06 Apr 2020 at 4:40pm

The magneto will work no matter what the battery voltage is, its not powered from the electric system, just by rotation.

Some starters will handle 12 volts though built for 6 volts, but not all will stand the voltage rise without internal damage.

The voltmeter is easier to install but since an alternator will put out more current than the old 6volt generator the ammeter needs to be replaced with one rated for at least as much current as the alternator. I prefer an ammeter on the battery charge and load wire so it can indicate whether the battery is taking a charge or is supplying loads. A voltmeter can't show the battery really charging unless it is connected to the battery posts, but when the tractor isn't used the voltmeter connected to the battery posts will run the battery dead in a few weeks.

And then the light bulbs all have to be replaced along with electric fuel gauge sensors and indicators.

There is an original wiring diagram in the shop manual:

http://geraldj.networkiowa.com/Trees/Allis-Chalmers-G-B-C-CA-Service.pdf

There have been alternator wiring diagrams posted on this forum in the past few days.

Gerald J.

This article is from ROD(NH)

Yea, if your just getting started on a project and checking it out, you DONT need an alternator right now... Just put in the 12 v battery with good cables and starter switch and get it going........ Put it on the portable charger once a month for battery maintenance... Mag is good to go.

I'm sorry,,, this question is getting to be a peeve of mine,,, does anybody have the intellect to do any research at all anymore? this question has prolly been asked 5,456,985 times on various forums, and there are prolly about 2,376,377 you-tube videos on how to do it...dammit, google, bing, ask, yahoo get you zillions of places to look....

Relax !!! 

TedBuiskerN.IL. wrote: My question is Why change?  Six volts will spin a B like a top if the correct heavy gauge wires are used.

Mine was converted to electric start with a different torque tube and flywheel. Someone did a very professional job of mounting the Genny under the seat and running it off the PTO shaft. I had the starter converted to 12 volt and run a 12 volt battery. Starts 10 times easier than the old 6 volt and I can get a battery anywhere they sell them. Still has the mag which I will get rid of sometime this summer.

that bracket look great Paul!

Dave, depending on how much you use the tractor, you might not even need to recharge the battery very often ?  You can put the 12 volt battery in place of the 8 volt and as you say, it will startup easy.... Just take the wires off the generator and tape them up so it will not charge and use the generator as a belt tensioner.... Then put the tractor on a plug in battery charger after you use the tractor . If you have a mag, it will run without recharge for several days. If you have a Distributor, then the coil is using the battery to form the SPARK and it will run the battery down in a day or two of use.... an external battery charger can be used as a temp "FIX" until you decided you want to install an alternator and rewire..... or maybe never.

My 2 cents in a short video- had I let the carb bowl fill before trying to start it, it would have lit off immediately.

6v pos. ground, generator cleaned, but otherwise stock, brushes replaced in starter, wiring replaced, rebuilt mag, all this 2 years go. The video is from April, hadn’t started since January, not on a battery tender. I used it regularly until October, started it once in January, then not again until April.

I contend that if everything is in good repair, 12v is completely unnecessary for reliable starting of a B. If additional or brighter lights or accessories are needed, 12v makes sense.

https://youtu.be/RUHDBlDCKSs


Edited by HoughMade - 03 May 2020 at 9:19pm