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Old 05-30-2018, 08:03 PM   #1
woofa.express
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Default question. simple starter motor conversion to 12v

I have busted 2 shafts on my starter motor, being 6v and running 12v system.


I have researched and there seems many ways to convert. The rest of the car has been converted. what is the most simple way. emphasis on simple. that's how I like things and that's why I like Model A's


thankyou in anticipation. gary
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Old 05-30-2018, 08:38 PM   #2
Mark DeRoseau
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Default Re: question. simple starter motor conversion to 12v

Replace the starter drive to a modern Bendix https://www.snydersantiqueauto.com/modern-starter-drive
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Old 05-30-2018, 09:23 PM   #3
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Default Re: question. simple starter motor conversion to 12v

There is a reason things are breaking! A 6V starter on 12V will deliver four times the torque, not just twice as much. Power =amperage squared times resistance. The amperage will double for a 6V starter on 12V. When you square that, you get 4X engagement slam force.

You can buy new 12V configuration starter field coils to make the conversion from the vendors. With the starter motor fields rewired from parallel to series, (making it a 12V starter) the average converted starter will still show almost 2X the power, but not so much as to severely abuse the drive.

As far as 'barrel' drives go, they are not without their own problems. The can and do fail and are extremely difficult to change on-the-road unless you carry a special tool to compress and expose the shrouded set screw.

When a barrel drive fails and locks in the extended position because the much finer helix shatters from excessive motor torque and poor off-shore manufacture and heat treating, the rear of the drive often cannot be compressed, even with the special removal tool, to access the set screw. It becomes hack saw and abrasive cutoff wheel time.

The motor field conversion is the only way to go. If you continue to slam the flywheel ring gear with a 6V starter on 12V you risk walking the ring gear off the flywheel.
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Old 05-30-2018, 09:26 PM   #4
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Default Re: question. simple starter motor conversion to 12v

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Originally Posted by woofa.express View Post
I have busted 2 shafts on my starter motor, being 6v and running 12v system.


I have researched and there seems many ways to convert. The rest of the car has been converted. what is the most simple way. emphasis on simple. that's how I like things and that's why I like Model A's


thankyou in anticipation. gary
The "6 volt field coils" get replaced with "12 volt field coils". That's it. It's actually pretty easy to do. If you have a good automotive starter and generator/alternator rebuilding shop near you (we have a couple in Houston) they can do it for you. You get the field coils from a Model A parts supplier, like Bratton's. If you have a good soldering iron to solder the field coils in, you can do it yourself.

Check your initial spark timing. That's will break starters.
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Old 05-30-2018, 10:22 PM   #5
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Default Re: question. simple starter motor conversion to 12v

I once bought a set of those 12v coils. Never again. I convert using the original ones. It is as simple as rearranging them so that they are all in series rather than two sets of two in series each connected in parallel. Thatís not easy to put in words but I hope you get it. This gives a field coil resistance 4 times what it was and reduces the power and torque to about the equivalent of running the in modified stater on 8 or 9 volts, I estimate.
Another way is to reduce the voltage getting to the starter. Iíve seen this done a number of ways including using a Bendigo spring in the +ve cable (I assume you converted to negative earth). Another way is to go to a wrecker and find a set of leads from a really small car - the ones that are not much thicker than a pencil. The longer the better. The small cables have a higher resistance and will cause a voltage drop, making life easier on the starter. There are several ways to go - these are just a couple for you to consider.
PS. Have you collected that gearbox yet? All Good?
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Old 05-31-2018, 11:39 AM   #6
Jim Brierley
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Default Re: question. simple starter motor conversion to 12v

I've been running 12v on a stock starter since 1960, never broke anything except 1 Bendix spring.
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Old 05-31-2018, 04:35 PM   #7
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Default Re: question. simple starter motor conversion to 12v

I agree with Jim Brierley. I've also been running a completely stock original 6 volt starter on 12 volts for many years without a problem , I did the same with Y block engines with good results . Back in the day 1954-55 six volt starters were to kill for .
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Old 05-31-2018, 04:40 PM   #8
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Default Re: question. simple starter motor conversion to 12v

Ran the 6 volt starter on 12 volts for many years without any problems.
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Old 05-31-2018, 04:44 PM   #9
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Default Re: question. simple starter motor conversion to 12v

I'm running a 6 volt starter on 12 volts with a modern Bendix drive and so far no problems. It's spinning a modified motor with 7:1 head
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Old 05-31-2018, 05:10 PM   #10
Purdy Swoft
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Default Re: question. simple starter motor conversion to 12v

I also run the modern starter drive with good results for the past 12 years .
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Old 05-31-2018, 07:01 PM   #11
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Default Re: question. simple starter motor conversion to 12v

I'm totally new to Model As, in fact I finally drove the '31 Coupe I bought last Summer for the first time today. I promised myself to finish a number of other started projects before I would do anything on the A. I'm now at 2.1 miles and counting.

It might be considered heresy that my plans are to do some hot rod type things like might have been done in the 40's or 50's but I'll give it a go anyway. I plan to retain the stock engine with mild mods and drive the car as much as possible so I want bright lights and reliability.

Since my question is starter related I thought I'd ask it here rather than starting another thread. I'm considering converting the car to 12V (I know - not 40's stuff) and since it is an older "survivor" car I'd plan to rewire everything on the car. While changing the starter to 12V, is there any big deal to convert to negative ground while I have it at my local starter/generator shop? I was afraid I messed up something today when I was getting the car started. I absent-mindedly hooked a 6V battery charger up as if it was negative ground. I finally realized my error and hooked it up correctly. With that little deal it made me think it would be nice to have it 12V negative ground just like everything else I own.

Thanks, in advance. Next I'll be asking about leaks that appear to be coming from both the front and back crankshaft seals.

Lynn
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Old 05-31-2018, 07:59 PM   #12
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Default Re: question. simple starter motor conversion to 12v

With respect, the fact that some of you have run 12v on a 6 v starter for years doesnít alter the fact that Woofa has broken 2 in a short time. I run 12 v on my cars but Iíve played with the starter too to prevent what has happened to Woofa. Iíve made my suggestions and answered a query from him by email. Letís see how he goes - hope he reports back.
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Old 05-31-2018, 08:36 PM   #13
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Default Re: question. simple starter motor conversion to 12v

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Originally Posted by Synchro909 View Post
With respect, the fact that some of you have run 12v on a 6 v starter for years doesnít alter the fact that Woofa has broken 2 in a short time. I run 12 v on my cars but Iíve played with the starter too to prevent what has happened to Woofa. Iíve made my suggestions and answered a query from him by email. Letís see how he goes - hope he reports back.


yeh, that's all correct mr Synchro and thankyou. however I must correct you. you see Woofa is my hound and can be viewed on my page. Woofa. express is my log on site. I say Woofa is my dog. Well that's not quite correct. Woofa was my dog until he was sadly retired by a Nissan Patrol. Never liked Nissan's since.
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Old 05-31-2018, 10:02 PM   #14
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Default Re: question. simple starter motor conversion to 12v

If you want to run negative ground, first reverse the battery cables to negative ground. reverse the wires at the coil and at the ammeter and you will be wired negative ground . The starter doesn't know the difference between negative or positive ground . if you feel that it is necessary go ahead and have 12 volt field coils installed in the starter or install them yourself if you can . you will either need to install a ballast resister at the coil or change to a 3.0 OHM coil . For the brightest head lights you will need to install at least a 60 amp alternator . change out the headlamp bulb to the 60-55 watt halogen bulbs The original type wiring harnesses will work just fine with the wires switched as mentioned above . the larger gauge wire will carry the higher voltage and amps with no problem . All of the parts are available in the common model A parts catalogs . If you choose to use a three OHM coil instead of a ballast resistor , you should be able to get one at NAPA . For better performance , I use the Pertronix flame thrower coil . I hope this helps .
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Old 06-01-2018, 05:49 AM   #15
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Default Re: question. simple starter motor conversion to 12v

That's the info and advice I was hoping to get. Thanks, Purdy Swoft!


Lynn
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Old 06-01-2018, 08:04 AM   #16
Bob Bidonde
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Default Re: question. simple starter motor conversion to 12v

I too have been running the original Model A starter on 12V for many years without any issues / failures. Please post a picture of the busted starter.
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Old 06-01-2018, 09:23 AM   #17
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Default Re: question. simple starter motor conversion to 12v

I have converted several starters from 6V to 12V using both rewiring the original coils to Series and buying new 12v coils. Either way is OK. The last 4 I converted I used new coils because I was in a hurry.
I have had the starter gear pushed off or starting to push off the flywheel on 3 cars. One was mine. But like some of the others, I ran them for years with no problem. My thinking is those that come off may be replacement starter gears. My car had a replacement gear.
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Old 06-01-2018, 10:09 AM   #18
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Default Re: question. simple starter motor conversion to 12v

I had a 6v starter that I ran on 12v with no problems BUT being the tinkerer that I am (I have been told more than once "You have too much time on your hands") and having two spare good 6v starters laying around, I combined the two to make two 12v starters buy swapping one sets of field coils from each starter and putting them in series. No cost but time (except for replacement brushes and "modern starter drive).
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Old 06-01-2018, 11:53 AM   #19
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Default Re: question. simple starter motor conversion to 12v

Quote:
Originally Posted by lake_harley View Post
That's the info and advice I was hoping to get. Thanks, Purdy Swoft!


Lynn
Lynn , you are very welcome .
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Old 06-01-2018, 11:58 AM   #20
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Default Re: question. simple starter motor conversion to 12v

woofa, 12v. wiring does not require heavier gauge wire as the amperage used is less than 6v. If you are interested in performance, e-mail me at jimb4e4@gmail.com for info on my performance how-to book.
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