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640 w/6V negative grnd?

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Andy

12-08-2002 05:21:19




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I have a 640 that won't start. It's been sitting up for years since my daddy passed away, and I'm trying to get it up and running again. It looks like it was set up as a negative ground system, and he never said anything about it being otherwise. I can jump it off a 12 volt directly to the starter, but I'm not sure how to test the rest of the electrical system out to see if indeed it is original 6V pos.grnd, or has been modified to a 6V neg grnd.

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Tim Dalrymple

12-09-2002 07:19:44




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 Re: 640 w/6V negative grnd? in reply to Andy, 12-08-2002 05:21:19  
Use a Multimeter to test the electrical system. Most digital meters will display a (-) sign in front of the voltage reading if you have the polarity backwards. (The red lead is positive, the black is negative)

Jump start the tractor, set the meter up to read 12 volts dc, usually the 20 volt setting on most meters. Place the leads on the battery, red to positive, black to negative. A 6 volt system should read around 7.5 to 8.5 volts if the charging system is working.

Be careful starting or running a 6 volt system with 12 volts. The coil is designed for a 6 volt battery and will produce more voltage than the points can handle. (The resistance of the 6 volt coil is 1/2 that of a replacement 12 volt coil, so the voltage will be double.)

If the tractor is charging properly, your problem could be as simple as corroded connections or a weak battery. It could also be that you need to rebuild the starter, which is not very difficult.

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Andy

12-09-2002 10:35:36




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 Re: Re: 640 w/6V negative grnd? in reply to Tim Dalrymple, 12-09-2002 07:19:44  
Thanks Tim,
I'll take a meter to it and try to learn my way thru it. I only jumped it off a 12 V directly to the starter to start it, it has a 6V in it.



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Tim Dalrymple

12-09-2002 12:05:11




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 Re: Re: Re: 640 w/6V negative grnd? in reply to Andy, 12-09-2002 10:35:36  
I converted my 4000 over to a 12 volt system. I found the Delco alternator and 3 ohm coil for free. I had to purchase 12 volt light bulbs and some wire loom. When I purchased my tractor, the previous owner was starting it with a 12 volt battery and then running it from the 6 volt system. None of the lights, or electrical guages worked. You can use the 6 volt guages, but you have to double the resistance of each guage with an external resistors. You could use your 6 volt coil, but you will need to install a balast resistor in series with the coil. (1.8 ohms I believe)

I did change from a positive ground to a negative ground when I did the conversion. The tractor now starts well even on very cold days.

Tim

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raytasch

12-08-2002 09:30:17




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 Re: 640 w/6V negative grnd? in reply to Andy, 12-08-2002 05:21:19  
It was a 6V positive ground when built. It should work either way if it is polarized the way it is hooked up.
ray



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RED

12-12-2002 20:35:31




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 Re: Re: 640 w/6V negative grnd? in reply to raytasch, 12-08-2002 09:30:17  
What is polarized ? and how do you do it ? RED



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