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Discussion Starter · #1 ·
Hi everyone. My name is Chuck and I am very glad I found this forum. About a year ago my uncle passed away he was 91 so he had a long and good life. He was a farmer for many years. He loved restoring antique John Deere tractors. Since he passed I have been helping my aunt maintain her property, cutting grass, trimming trees, etc. My uncle has 4 restored antique tractor’s that have been sitting idle for over 5 or 6 years now. She wants to sell the tractors but I would like to have them running before we do that. So I decided to try and get these tractors started one at a time. He has a 1960 John Deere 630 Row Crop Gas Motor, 1959 John Deere 730 Row Crop Gas, 1936 John Deere “B” Gas and a 1947 Farmall “H”. So just to let ya”ll know….I know nothing about tractors. I am mechanically inclined though. Just not in the tractor area. So here’s the first couple questions in regards to the 630 and 730 and I really appreciate any and all help. So what is the purpose of positive ground and if this is a 12V system does it require a 12V ignition coil? Not really understanding the two 6V batteries vs just one 12V battery. My brother in law and I installed new batteries in the 730 and 630. The tractors will turn over fine but there is no spark. I replaced the coils but used 6 volt coils because I thought that‘s what was originally installed. Trying to buy the right parts from a supplier hasn’t worked out that well because a lot of these parts have vague descriptions. Thanks for your help in advance! Chuck
 

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Hello and welcome. To try and answer your questions.
Positive ground was used on most all vehicles that had a generator to produce d/c electricity. Since electricity actually flows from negative to positive it makes better control. Alternators produce a/c voltage which is then converted to d/c more efficiently than generators. Doesn't really matter in theory which polarity one uses. Manufacturers chose negative to be the common carrier or "ground."
Normally a 12v system uses a 12v coil. However not knowing what your uncle did to convert them. He could have used a bigger resistor to drop the voltage to the coil.
The two batteries was a space thing for John Deere to get enough amperage to start the tractors. Wired ( + to + )_and ( - to - ) for six volt, or (+ to - ) for 12 volt. Take a voltmeter and start at the coil then work your way back to see where you're losing voltage. If you have the proper voltage at the coil try changing the distributor components.
 
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Howdy Chaz and welcome to ATF! Dave provided some good info to begin looking for your electrical problems. I believe with any of them one could go to the points if they have distributors , and with the switch on open and close the points with a small screwdriver to see if a spark is produced. That will tell you if you have power to that point. Also try filing the points while in the distributor if there is no spark. If the points will spark your problem may be confined to the rotor, distributor cap, or wires. Condensers have been a source of electrical trouble for me in recent years.
 
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Discussion Starter · #4 ·
Thank You Big Dave and Jim for your quick reply. I’m pretty sure I have the positive ground/ 6 volt batteries figured out thanks to your replies! As it turns out I did buy 12V coils for these 2 tractors. I also know that they are internally resisted there is a primary and secondary coil encased in the coil housing. Even though I bought these new I want to check them to make sure they are good. Would anyone know what the ohm reading should be for the primary and secondary coil? The 630 tractor has a Delco Remy distributor and the 730 has a Wico distributor. I am going to go ahead and buy new, points, plugs, rotor, cap, wires and dust plate. I have been able to find all the parts with the exception of the dust plate for the Wico distributor. Thanks again for all your help! I really appreciate it! Chuck
 

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A standard 12v ignition coil should have around 1.5 to 2.5 ohms roughly on the primary winding and 10,000 to 11,000 on the secondary. An internal resisted coil should be about double that 3 to 4.5 ohms on the primary and about the same on the secondary as a standard coil.
 
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Discussion Starter · #6 ·
Hi Dave….thanks for your reply! The 2 coils that I had recently purchased may be a little weak. The primary side reads at 3.1 on one of the coils and 3.3 on the other. The secondary on both read at 9.7 and 9.8. Do you think that being just below the 10,000 would make a huge difference? Thanks in advance!
 

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Sounds good to me. (y) Those are rough numbers from memory. As long as you're close things should be good.
 
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Discussion Starter · #8 ·
Thanks Dave! I ordered all the ignition parts with the exception of the Wico distributor dust plate yesterday. Couldn’t find that dust plate anywhere. Any ideas on where I might find one..and is it even needed just to start the tractor? One last question before I install the parts. Since these tractors are positive ground how are the coils wired? Do you attach the positive wire to the negative side of the coil and negative to positive side? Actually there may be more questions as I go😉. Thanks for all your help! Ya’ll are a Godsend!
 

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Welcome to the forum!
 
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Discussion Starter · #10 ·
Thank you oliverguy…nice to meet ya! This forum has been a blessing for me..especially for someone who knows very little about tractors. That has taken on the task of getting a few of them running again.
 

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Since these tractors are positive ground how are the coils wired? Do you attach the positive wire to the negative side of the coil and negative to positive side?
No, Keep the polarity intact. I worked with electricity my whole career and I never liked the term "ground" it is misleading. There is an energized line and a common line and with DC voltage really doesn't matter which polarity one uses.
There are two main reasons that the electrical system is bonded to the tractor chassis.
One, to save the company a little money being able to not run two wires to every device. Two, so if something shorts to the frame one doesn't get electrocuted when touching the tractor. Now number two might be more important to most folks, number one is more important to the companies.

Couldn’t find that dust plate anywhere. Any ideas on where I might find one..and is it even needed just to start the tractor?

There is a plethora of aftermarket parts stores on the internet, but it may not be available as is the fact for these 60+ year old tractors. I have seen a lot of tractors, and cars as well, running without the dust cover in the distributor.

I'm going to move this thread to the John Deere section as it has become quite more than an introduction.
 
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