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Old 02-26-2011, 10:51 AM   #1
Patrick
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Default Starter field coils and cranking speed

The Model A that I purchased had been converted to 12v. The compression is excellent, but the engine seems to turn over to fast when it is cranked. I have three questions.
1. Does the cranking RPM's change with a 12v field coil in the starter.? If so will it be slower or faster?
2. Is there any way of telling which coils are in the starter now?
3. If the coils are correct is there any way to slow down the cranking. I do not want to damage my bendix or ring gear .
Thanks in advance.
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Old 02-26-2011, 11:29 AM   #2
Tom Wesenberg
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Default Re: Starter field coils and cranking speed

A longer thinner starter cable would drop the current and speed.

A 6 volt battery would be my choice to make the speed correct, but many think they have to go to 12 volt because 12 volt batteries are easier to find. If I thought my battery was near the end of it's life, I'd replace it before I left home, but even on the road, I can't imagine not finding a 6 volt battery at almost any auto parts store or farm store.
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Old 02-26-2011, 11:33 AM   #3
CWPASADENA
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Default Re: Starter field coils and cranking speed

It sounds to me that you still have 6 Volt Coils in the starter. It was not uncommon at all to not change the starter fields when converting to 12 Volts, especially if it was an older conversion. I think the correct coils will slow down the starter.

Chris

Last edited by CWPASADENA; 02-26-2011 at 11:35 AM. Reason: Typo
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Old 02-26-2011, 11:43 AM   #4
CWPASADENA
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Default Re: Starter field coils and cranking speed

Quote:
Originally Posted by Tom Wesenberg View Post
A 6 volt battery would be my choice to make the speed correct, but many think they have to go to 12 volt because 12 volt batteries are easier to find. If I thought my battery was near the end of it's life, I'd replace it before I left home, but even on the road, I can't imagine not finding a 6 volt battery at almost any auto parts store or farm store.
I agree,

All of My old Fords are 6 volt. I use Optma Batterys which will hold it's charge very well and last a long time 7-10 years, and they do not require maintenance. If your electrical system is in good condition, you should have good results.

I feel, for the most part, a 12 volt conversion is just an aspirin tablet for a sub-standard electrical system.

Again, this is just my opinion,

Chris
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Old 02-26-2011, 11:44 AM   #5
Kurt in NJ
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Default Re: Starter field coils and cranking speed

I have been told that my car cranks too fast,I must have 12 volts, but I only have 6V system, properly restored the 6V system is more reliable.

a heavy duty dropping resistor can be used to reduce the voltage to the starter , or a long cable --but there is still the high inital inrush because of the cold resistor, the starter will still "hit" the ring gear hard, then crank slower.

you can compare the windings you have now with original windings, and with a late 50s starter that is 12v, I suspect the "12v" fields sold for use on the A are what is used on the 50s 12v starters for V8, it looks much like a flathead starter, and the flathead field windings are close to A


you could find an old neglected starter with worn bushings so the armature drags on the field pieces, smear some grease on the brushes.
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Old 02-26-2011, 11:44 AM   #6
Pa Joe
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Default Re: Starter field coils and cranking speed

Partick, you might get different opinions on this but the only thing I did was replace the starter drive with a modern starter drive. It's more suited for 12V. No spring bolts to snap off. Which was common. In the past I converted a 36 and a 40 Ford to 12V with no ring gear problems. Snyders sells them for around 25.00
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Old 02-26-2011, 12:06 PM   #7
Special Coupe Frank
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Default Re: Starter field coils and cranking speed

FWIW in terms of cranking speeds, my un-restored '28, with a tired 84,000 mile engine, on six-volts cranks at about 15 compression-impulses ("grunts") in 5 seconds
( that's about 5 c-i / second ). (Very similar to our old Ford 9N tractor)

If the temps are down around 0* F, it slows-down to about 10 c-i / 5 seconds, or 2 c-i / sec.

5 c-i / sec seems to be the maximum cranking speed for my car, whether the engine is at 32* F or fully warmed-up.

If yours sounds like a blender, I'd bet the starter still has 6-volt fields in it.
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Old 02-26-2011, 02:07 PM   #8
johnbuckley
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Default Re: Starter field coils and cranking speed

Is there any truth in the the story that when Ford went over to 12 volt the starter coil specification stayed the same? I'm inclined to believe it as I've been putting 12v through my nominally 6v starter for over a decade without any problem.
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Old 02-26-2011, 06:07 PM   #9
Herb Concord Ca
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Default Re: Starter field coils and cranking speed

Hi Patrick, I'll try to answer your 3 questions.
1) a 12V battery connected to a 6V starter will turn faster than a 12V starter. A 12v battery and 12V starter will turn a little faster than a 6V battery and a 6V starter.

2) a 6V starter will have the 4 coils wired in series/parallel. A 12 V starter will have the 4 coils wired in series. Another way to check, coils wired for 12 Volts will have only 1 coil connected to the copper button, coils wired for 6Volts will have 2 coils connected to the copper button.
Also on 12 volt wired coils, both insulated brushes will be connected to one field coil.

3) If your starter is really wired for 12 volts and you think it runs too fast follow Tom's suggestions.

Regards,
herb, with a 12 volt battery (and rewired starter) needed for my AC unit in my 31 slant town sedan.
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Old 02-26-2011, 07:27 PM   #10
Patrick
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Default Re: Starter field coils and cranking speed

Thanks for the field coil data Herb
. I guess the best thing for me to do is take the starter apart and check out how everything is wired up.
I agree with everyone about keeping the orig 6volt in place. I purchased this car after it was converted with a new altenator etc.
I did convert to 12 halagon lights........... Wow o Wow what a difference on those country roads driving at night.
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